Diagnosis (modified from Carlgren, 1949; Uchida, 2007; modifications in bold): Actinernidae with thick column distally expanded, usually forming eight lobes. No marginal sphincter musculature. Tentacles, except youngest and rarely inner ones, with aboral thickenings of varying development that may run up the tentacles almost to their tips. Arrangement of tentacles usually in two cycles, largest tentacles at apices of lobes. Longitudinal muscles of tentacles ectodermal, weak, radial muscles of oral disc ectodermal. Two well-developed siphonoglyphs. Numerous perfect mesenteries; after the first 10 pairs (first and second cycles), mesenteries appear bilaterally in the middle point of each of the eight lateral endoceles, and are unequally developed. Retractors and parietobasilar musculatures weak. Cnidom: Spirocysts, basitrichs, b-mastigophores, p-mastigophores A.

Type species: Actinernus nobilis Verrill, 1879, by original designation.

Valid species: Actinernus. antarcticus (Carlgren, 1918); A. elongatus (Hertwig, 1882); A. michaelsarsi Carlgren, 1918; A. nobilis; A. robustus (Hertwig, 1882) (Rodríguez and López-González, 2013).

Material: Holotype AMNH 4028 (1 specimen); locality: ANT XIX/3, ANDEEP I Program, RV Polarstern, Sta. PS61/114–10, Southern Ocean, Drake Passage, Antarctica, 61°43.70′ S 60°42′ W, collected on 19 February 2002 (2853–2856 m). Paratypes AMNH 4078 (3 specimens, same collection data as holotype). Paratype AMNH 4035 (1 specimen, same collection data as holotype). MNRJ 8183 (3 specimens); locality: Ak. Ioffe Cruise 29, Superestação 10, Sta. 202, series #1044, South Mid-Atlantic Ridge, 33°40.07′ S 23°05.57′ W, collected on 23 November 2009 by MAR-ECO #38216 (4740 m).

Material examined: Actinernus michaelsarsi: USNM 88367/386969 (1 specimen; holotype); locality: United States, North Atlantic Ocean, Blake Plateau, 350 mile ESE of Charleston, South Carolina at the Wreck Site of S.S. Central America, 31°30′ N 77°00′ W, collected Sept 1989 by Columbus America Discovery Group; Herdendorf, C. E.; Evans, R.; by Arctic Discoverer R/V and Nemo DSR/V (2200 m). Porponia antarctica Carlgren, 1914: NMSZ 1921.143.1756 (2 specimens; syntypes); locality: Scotia Collection, off Coats Land, 71°22′ S 16°34′ W, collected on 16 March 1904 (2578 m). NMSZ 1921.143.1756 (1 specimen; syntype, same collection data as other syntypes). Porponia elongata Hertwig, 1882: NHM 1889.11.25.29 (2 specimens; syntypes); locality: Challenger Collection, Sta. 160, collected on 13 March 1874 (4755 m). Porponia robusta Hertwig, 1882: NHM 1889.11.25.30 (1 specimen; holotype); locality: Challenger Collection, Sta. 237, 34°37′ N 140°32′ E (3429 m). Isactinernus quadrilobatus Carlgren, 1918: UUZM [Typsamlingen nr 102 a (Anthozoa)]. Syntype. “Dr Sixten Bocks Japan Exp. 1914, KIUSCHIU, Goto Islands, Osesaki, 23 miles NV t.V 1/2V–122°10′ Ost, 165 m, datum: 14/5, formol, Type” (1 specimen). UUZM [Typsamlingen nr 102 b (Anthozoa)]. Syntype “Dr Sixten Bocks Japan exp. 1914, KIUSCHIU, Goto Islands, Osesaki, c.a 170 m, datum: 14/5, formol, Isactinernus 4-loba-tus orig: determ. Carlgren” (1 specimen). Synactinernus flavus Carlgren, 1918: UUZM. [Typsamlingen nr 232 (Anthozoa)]. Holotype. “Dr Sixten Bocks Japan Exp. 1914, KIUSCHIU, Goto Islands, 28 miles N, 1/2 Ost frain Shirase fyr, 128°50′ O.L. 33°41′ N Br, 110 m, datum: 17/5; botten: sand, formol. Synactinernus flavus orig: determ. Carlgren.”

External anatomy (fig. 2): Body short and broad in preserved specimens, with an inverted triangle shape (fig. 2A, B). Pedal disc well developed, small, flat or slightly curved, rectangular; up to 8 mm in diameter in preserved specimens (fig. 2B). Column smooth, not divisible into regions, widened distally, rectangular (flattened in one axis) (fig. 2A, B); with cartilaginous texture (fig. 2B). Column up to 31 mm in diameter and 39 mm in length in preserved specimens. Oral disc wider than column in preserved specimens (fig. 2B), forming at least four lobes (fig. 2C) in preserved specimens and eight in live ones (fig. 2A). Oral disc up to 44 mm in diameter in preserved specimens; apparently nonretractable. Margin of column tentaculate (fig. 2A, B, D). Tentacles 59–62, long, very slender, pointed, of “filamentous” aspect (fig. 2A–C), with prominent mesogleal basal aboral thickenings of triangular shape in preserved specimens (fig. 2D, E); longest tentacle up to 15 mm.

Internal anatomy and histology (fig 2): Marginal sphincter musculature absent (fig. 2F). Base of tentacles with mesogleal aboral thickening (fig. 2F, G); longitudinal tentacle musculature ectodermal (fig. 2H). Actinopharynx short, approximately one third of column's length, longitudinally sulcated throughout. Two sectioned specimens with up to 46 mesenteries in four cycles distally (6+4+8+5 pairs) (fig. 2J); mesenteries after first 6 pairs on lateral endoceles of first cycle with retractor muscles as in directives; after second cycle (6+4 = 10 pairs), mesentery formation bilateral in middle zone of lateral endoceles. All mesenteries perfect, including two pairs of directives, each associated with one siphonoglyph (fig. 2I–J), except 4–8 imperfect mesenteries (depending on specimen) of third and fourth cycles. In third and fourth cycle, mesenteries within same pair unequally developed (fig. 2K). More mesenteries distally than proximally. Thirty-five mesenteries proximally in three cycles; all mesenteries with filaments and gametogenic tissue. All specimens collected in November sterile; those collected in February with weakly developed spermatic cysts in all mesenteries. Retractors of all mesenteries weak, short, diffuse (fig. 2L), difficult to discern; parietobasilar musculature very weak in all mesenteries (fig. 2M). Basilar musculature of mesenteries absent (fig. 2N).

Cnidom (fig. 3): Spirocysts, basitrichs, b-mastigophores, p-mastigophores A, and holotrichs. See figure 3 and table 1 for size and distribution.

Distribution and natural history: Specimens of Actinernus mercedae, sp. nov., were collected in the Southern Ocean in the Drake Passage (61°43.70′ S, 60°42.62′ W) between 2852–2856 m, and in the South Atlantic, east of the Mid-Atlantic Ridge at 4740 m depth.

Etymology: This species is named after Mercedes Conradi (Universidad de Sevilla, Spain), who kindly collected, photographed, and preserved specimens of the new species for the first time.

Remarks: After the revision of the type material and newly collected material, Rodríguez and López-González (2013) considered five valid species for Actinernus: A. antarcticus, A. elongatus, A. michaelsarsi, A. nobilis, A. robustus, and two new undescribed species from Antarctica (E.R., personal obs.). Uchida (2007) considered the same five valid species of Actinernus. Contra Fautin (2016), Rodríguez and López-González (2013) formalized this point of view on the membership of Actinernus, rejecting the synonymy of A. antarcticus and A. elongatus by Dunn (1983) and considered A. antarcticus valid. Here we describe Actinernus mercedae, which is placed within the genus due to its lobed column that is more developed distally, absence of marginal sphincter musculature, distinct mesogleal thickenings on aboral side of tentacles, mesenterial arrangement following the Endocoelantheae plan (see Carlgren, 1949), two siphonoglyphs and weak retractor and parietobasilar musculatures. Actinernus mercedae resembles other two genera within the family (Isactinernus Carlgren, 1918, and Synactinernus Carlgren, 1918) because it has a lobed distal column (Carlgren, 1949; Uchida, 2007). However, it can be easily distinguished from those genera because of the bilateral arrangement of the younger mesenteries in Actinernus (cyclic in the other two genera, Carlgren, 1918; Uchida, 2007; Izumi et al., 2019) and the distinct mesogleal aboral thickenings in the base of the tentacles in Actinernus (not distinct in the other two genera) (Izumi et al., 2019); furthermore, the lobes in species of Actinernus are not as marked as those in the other two genera (see Izumi et al., 2019). Actinernus mercedae is the third species of the genus described for the Southern Ocean: Actinernus antarcticus and A. mercedae are present in the Atlantic portion of Antarctica whereas A. elongatus is known from the sub-Antarctic Indian Ocean. Because the internal anatomy of members of Actinernus is often hard to observe due to preservation issues, the only characters to show consistent anatomical differences between the valid species of Actinernus in the Southern Ocean are the development and shape of the basal aboral thickenings of the tentacles (Rodríguez and López-González, 2013). However, the number of mesenteries and their arrangement and their perfect or imperfect nature also seem to differ among the species. Actinernus mercedae is easily differentiated from all other species of the genus in the Southern Ocean by the more or less defined oral disc lobes with very conspicuous triangular mesogleal aboral thickenings in tentacles (fig. 2A). Though Dunn (1983) hypothesized that the lobes in the oral disc of Actinernus spp. are artefacts of the contraction of tentacles (Fautin and den Hartog, 2003), specimens of A. mercedae display lobes in the oral disc even in extended state (fig. 2A). Actinernus mercedae can be differentiated from A. elongatus by the rounded mesogleal aboral thickenings in tentacles of this species, and by the gradual decrease in diameter between the basal aboral thickenings and the tentacles as well as for the morphology of the tentacles themselves in A. antarcticus (i.e., filiform tentacles in A. antarcticus vs. filamentous tentacles in A. mercedae) (see fig. 4). In addition, the number of mesenteries differs between A. antarcticus and A. mercedae (i.e., up to 68 mesenteries in A. antarcticus vs. 46 in A. mercedae; see Carlgren, 1914, 1918, for A. antarcticus). Given our current lack of understanding about the distribution of cnidae in species of Actinernus, we should not use this character for specific identification (Rodríguez and López-González, 2013). However, we acknowledge that the cnidae of our specimens differ from that of A. antarcticus in the presence of spirocysts and two categories of p-mastigophores A in the column; presence of p-mastigophores A and lack of b-mastigophores and small basitrichs in tentacles; lack of spirocysts and smaller basitrichs and presence of two kinds of p-mastigophores in the filament. Geographic distribution also varies among valid species of Actinernus in the Southern Ocean: A. antarcticus is known from Antarctic waters (Kapp Norvegia and Antarctic Peninsula) whereas A. elongatus is known from sub-Antarctic waters of the Indian Ocean. Actinernus mercedae is known from its type locality in the Drake Passage and in the South Atlantic outside the sub-Antarctic region (∼33° S) at depths similar to records of A. elongatus (i.e., 4750 m) (Rodríguez and López-González, 2013). Of the three species of Actinernus distributed in the northern hemisphere, Actinernus mercedae resembles A. robustus from Japan in the shape of the tentacular mesogleal aboral thickenings and lobed column (see Hertwig, 1882; Carlgren, 1918; Uchida, 2007). The circumscription of characters in A. robustus is not very clear since the single specimen examined and described by Carlgren (1918) besides the holotype (that of Hertwig, 1882) differs relative to the holotype (i.e., large specimen: up to 75 mm in column height and up to 190 tentacles, eight lobes of similar size, companions in younger developing pairs of mesenteries of similar size, depth 150–600 m) to the holotype and the additional material examined by Uchida (2007), i.e., up to 40 mm height and up to 90 tentacles, eight lobes divided in four bigger and four smaller ones, companions in newly developed pairs of unequal size, depth 1115–3429 m.These differences led Uchida (2007) to hypothesize that there are probably two species in Japan. In addition, Uchida's interpretation of the formation of the mesenteries in Actinernus differs slightly from that of Carlgren (1918, 1949). Although both authors agree in that after the second cycle mesenteries appear bilaterally in each of the lateral endoceles, for Uchida (2007) new pairs of mesenteries appear in the middle zone of each of the eight lateral endoceles and are of unequal size, whereas for Carlgren new mesenteries in a pair usually grow from the outer side of the octant inward and are of similar size (Carlgren, 1918, fig. 13). Corroborating the formation and arrangement of the younger pairs of mesenteries is hard in these species because of the weak and diffuse nature of the retractors and its preservation in the rather few specimens available. In the examined specimens of A. mercedae (AMNH 4078, MNRJ 8183) unequally developed companions corresponding to the third and fourth cycle of mesenteries are present in the same octant at the actinopharynx level, whereas in A. robustus mesenteries companions of a pair are of unequal size from the fourth cycle on in the same octant at a similar level (Uchida, 2007). There are also differences in the cnidae of both species (see table 1 and Uchida, 2007): p-mastigophores A in the tentacles of A. mercedae are absent in A. robustus and basitrichs in the tentacles A. mercedae are longer than in A. robustus; two categories of p-mastigophores in the column of A. mercedae are absent in A. robustus and basitrichs present in the column of A. robustus are absent in A. mercedae; a category of short basitrichs in the actinopharynx A. mercedae is absent in A. robustus; one category of p-mastigophores A and b-mastigophores in the filaments of A. mercedae are absent in A. robustus which also has holotrichs in the filaments that are absent in A. mercedae. The two species from the North Atlantic (A. michaelsarsi and A. nobilis) can be differentiated from A. mercedae by the weak mesogleal aboral thickenings of their tentacles (prominent in A. mercedae) and by the number of tentacles (59–62 tentacles in A. mercedae vs. approximately 120 tentacles in A. nobilis and 70 in A. michaelsarsi) (Uchida, 2007). We also find some variability within specimens of A. mercedae from the Southern Ocean and the SMAR (e.g., cnidae); however, we attribute these slight differences to interpopulation variability. Actinernus mercedae is the sixth species of the genus worldwide. Authorship of this species recognizes P. López-González's contribution to earlier work that is included in this larger manuscript.

Diagnosis (modified from Carlgren, 1949; modifications in bold): Actinostolidae with well-developed pedal disc and rather thick column; tentacles covered by distal column. Mesogleal marginal sphincter musculature weak or fairly well developed. Tentacles short, inner ones considerably stronger than outer ones and about half as numerous as mesenteries; aboral base of tentacles often thickened. Longitudinal muscles of tentacles and radial muscles of oral disc mesogleal. Two broad siphonoglyphs. Often 16 pairs of perfect mesenteries with a variable number of pairs with one perfect and one imperfect mesentery. Arrangement of mesenteries not as regular as in Actinostola, but with strong tendency to unequal development of mesenteries in a pair. Retractors weak, diffuse, and parietobasilar and basilar musculatures well developed. Mesenteries differentiated into stronger, fertile mesenteries with well-developed filaments and into weaker fertile mesenteries without filaments proximally h do not reach the distalmost part column. Cnidom: spirocysts, basitrichs, p-mastigophores A.

Type species: Sicyonis crassa Hertwig, 1882, by original designation.

Valid species: Sicyonis careyi Eash-Loucks and Fautin, 2012; S. crassa; S. erythrocephala (Pax, 1922); S. gossei (Stephenson, 1918b); S. haemisphaerica Carlgren, 1934; S. heliodiscus Sanamyan et al., 2015; S. ingolfi Carlgren, 1921; S. obesa (Carlgren, 1934); S. sumatriensis Carl- gren, 1928a; S. tuberculata Carlgren, 1921; S. tubulifera (Hertwig, 1882); S. variabilis Carlgren, 1921 (Fautin, 2016).

Material: MNRJ 8167 (4 specimens); locality: Mid-Atlantic Ridge, Ak. Ioffe Cruise 29, Superestação 7, Sta. 201, series #1030, 29°27.12′ S 10°08.72′ W, collected on 20 November 2009 by MAR-ECO #38295, Shirshov St. 2184–5 (4120 m).

Material examined: Stomphia selaginella (Stephenson, 1918a): AMNH 4326 (20 specimens); locality: ANT XV/3 Cruise, EASIZ II Program, RV Polarstern, Sta. PS48/220, Southern Ocean, Antarctica, Weddell Sea, Austassen, 70°50.40′ S 10°35.40′ W, collected on 19 February 1998 by P. López-González (236 m). Actinostola crassicornis (Hertwig, 1882): AMNH 4698 (3 specimens); locality: ANT XIX/5 Cruise, LAMPOS Program, RV Polastern, Sta. 61/153, Burdwood/Namuncurá Bank, 54°31.22′ S 56°08.93′ W, collected on 6 April 2002 by E. Rodríguez (277 m). Actinostola georgiana Carlgren, 1927: AMNH 4803 (1 specimen); locality: ANT XXI/2 Cruise, BENDEX Program, RV Polarstern, Sta. PS65/019-1, Southern Ocean, Bouvet Island, 54°30.09′ S 03°14.13′ W, collected on 24 November 2003 by E. Rodríguez (247 m).

External anatomy (fig. 5): Pedal disc small, circular, flat, 25–40 mm in diameter in preserved specimens (fig. 5A). Column firm, cylindrical, tall, smooth, not divisible into regions (fig. 5A); margin tentaculate (fig. 5B). Column white/light beige (fig. 5A); 35–50 mm in diameter and 10–49 mm in length in preserved specimens. Oral disc circular, as wide or slightly wider than column, with central mouth, same color as column (fig. 5B); 30–48 mm in diameter in preserved specimens. Tentacles approximately 132, smooth, short, pointed, with no markings, in 2–3 cycles on outer half of oral disc (fig. 5B); all tentacles translucent beige in preserved specimens (fig. 5B). Inner tentacles slightly longer than outer ones (fig. 5B); longest tentacle up to 18 mm in preserved specimens.

Internal anatomy and histology (fig. 5): Body-wall thickness uniform throughout column with thin gastrodermis and thick mesoglea (fig. 5C); epidermis of column mostly absent (fig. 5C). Marginal mesogleal sphincter musculature weak, diffuse, with fibers mostly close to gastrodermis and narrow proximally (fig. 5C); muscle fibers with reticular arrangement in mesoglea (fig. 5D). Longitudinal musculature of tentacles mesogleal (fig. 5E).

Mesenteries irregularly arranged in five cycles, 68 pairs at midcolumn; more mesenteries proximally than distally. Approximately 16 mesenteries of first and second cycles, perfect, including two pairs of directives, each associated with one siphonoglyph (fig. 5F); third to fifth cycles imperfect, with filaments (fig. 5F, G). Fifth cycle of mesenteries imperfect, fertile (fig. 5F). Mesenteries in pairs of third to fifth cycle unequally developed (fig. 5G). Anomalous pair of fourth cycle fused (fig. 5J). Oocytes 1–5 per mesentery in various stages of development, including pre- and early vitellogenic oocytes (fig. 5L, M), with trophonema (arrow: fig. 5M). All specimens collected in November female; major axis of oocytes up to 0.9 mm. Species inferred gonochoric. Retractors of all mesenteries weak, diffuse (fig. 5G–I); parietobasilar of larger mesenteries well developed with free mesogleal flap (fig. 5I); rest of mesenteries with weak to indistinct parietobasilar musculature (fig. 5K).

Cnidom (fig. 6): Spirocysts, basitrichs, p-mastigophores A. See figure 6 and table 2 for size and distribution.

Distribution and natural history: Sicyonis erythrocephala was originally recorded from the Bellingshausen Sea in the Antarctic Peninsula (Pax, 1922; Carlgren, 1927). After Fautin (1984) synonymized S. aurora Carlgren and Stephenson, 1929, and S. antarctica Carlgren, 1939, with S. erythrocephala, the species is also known from Tasmania (Carlgren and Stephenson, 1929), off Coats Land in the Weddell Sea (Carlgren, 1939) and all around Antarctica up to 42° S (Fautin, 1984). Thus, S. erythrocephala is mostly a widespread Antarctic species distributed in three districts of the Southern Ocean (i.e., Atlantic, Pacific, and Indian sensu Rodríguez et al., 2007). Our material significantly extends the geographic range of the species further north to the SMAR (∼29° S) and is the deepest record for the species, extending the bathymetric range of the species from 3879 m to 4120 m.

Remarks: Our material is identified as a Sicyonis based on a combination of a mesogleal longitudinal musculature in the tentacles (absent in Tealidium Hertwig, 1882; Anthosactis Danielssen, 1890; Paranthus Andres, 1883; Bathydactylus Carlgren, 1928a; Antiparactis Verrill, 1899; Pseudoparactis Stephenson, 1920; Antholoba Hertwig, 1882), unequal development of mesenteries in a pair (absent in Pycnanthus McMurrich, 1893; Hormosoma Stephenson, 1918a; Cnidanthus Carlgren, 1927), absence of b-mastigophores in tentacles (present in Actinostola Verrill, 1883; Stomphia Gosse, 1859), and number and cycles of mesenteries and pseudotentacles present in Ophiodiscus Hertwig, 1882 (Carlgren, 1949; Fautin, 1984; Rodríguez et al., 2008; Eash-Loucks and Fautin, 2012). It can be further differentiated from Parasicyonis Carlgren, 1921, by the presence of filaments in fertile mesenteries (present in Parasicyonis; absent in S. erythrocephala) and number of perfect mesenteries (some mesenteries of fourth cycle perfect in Parasicyonis; no mesenteries of fourth cycle perfect in S. erythrocephala) (Carlgren, 1921, 1949; Rodríguez et al., 2008; Eash-Loucks and Fautin, 2012). From Synsicyonis Carlgren, 1921, our specimens can be differentiated by the number of cycles of mesenteries (four in Synsicyonis; up to six in Sicyonis and five in S. erythrocephala) and the fertility of the mesenteries (third cycle of mesenteries fertile in Synsicyonis; only fourth cycle of mesenteries fertile in S. erythrocephala) (Carlgren, 1921, 1949; Rodríguez et al., 2008).

Sicyonis is a deep-sea genus of poorly known species whose identification is difficult due to unknown variability in diagnostic morphological characters (Molodtsova et al., 2008). Despite these difficulties, our specimens agree with the description of the external and internal anatomy given by Carlgren (1927) for S. erythrocephala. Except for the size of the nematocysts in the tentacles and actinopharynx, which are closer to the measurements given by Carlgren (1939) than those from Carlgren (1927), our specimens show only slight differences in the number of mesenteries described for S. erythrocephala: they have 68 pairs whereas Carlgren recorded 70 and 88 pairs (Carlgren 1927, 1939, respectively). The differences in number of mesenteries could be due to the different size of specimens or the difficulty in counting mesenteries in general, but especially in badly preserved deep-sea specimens. It is important to note that S. erythrocephala falls into a group within Actinostolidae that, in general, does not follow the Actinostola rule, even indistinctly (Sanamyan et al., 2015). This is seen in our specimens of S. erythrocephala in which small differences within a pair can be observed only in the histological sections (fig. 5G), but not in the dissections. Sicyonis erythrocephala can be differentiated from five of the species of the genus by features of the tentacles: development of the basal aboral thickening of the tentacles (present in S. erythrocephala; absent in of S. variabilis), basal aboral thickening projecting as large swollen bulb (absent in S. erythrocephala; present in S. tuberculata), number of tentacles (132 in S. erythrocephala; 144 in S. gossei; 200 in S. tubulifera), morphology of tentacles (wartlike in S. crassa; filiform in S. erythrocephala), and distribution of tentacles in oral disc (marginal in S. heliodiscus; outer half of oral disc in S. erythrocephala). Sicyonis erythrocephala can be further distinguished from the other species of the genus by the marginal sphincter musculature (well developed in S. hemisphaerica and S. sumatriensis; weak in S. erythrocephala) and its nature (alveolar proximally and distally in S. carey; reticular throughout in S. erythrocephala)

Diagnosis (modified from Carlgren, 1949; modifications in bold): Actiniidae with well-developed pedal disc. Column elongated, smooth. Endodermal marginal sphincter musculature diffuse. Tentacles long, hexamerously arranged on outer half of oral disc; each tentacle with an endodermal sphincter at its base, by the contraction of which it may be thrown off the longitudinal muscles ectodermal. Siphonoglyphs well developed. Perfect pairs of mesenteries more or less numerous, two pairs of directives. Retractors diffuse. Mesenteries not more numerous at margin than at limbus. Cnidom: spirocysts, basitrichs, p-mastigophores A.

Type species: Actinia tuediae Johnston, 1832.

Valid species: Bolocera africana Pax, 1909; B. kensmithi Eash-Loucks and Fautin, 2012; B. kerguelensis Studer, 1879; B. maxima Carlgren, 1921; B. novergica Pax, 1909; B. pannosa McMurrich, 1893; B. paucicornis Dunn, 1893; B. somaliensis Carlgren, 1928a; B. tuediae (Fautin, 2016).

Material: MNRJ 8175 (1 specimen); locality: Ak. Ioffe Cruise 29, Shirshov st. 2184–5, Superestação 1, Sta. 201, series #1030, Mid-Atlantic Ridge, 29°27.12′ S 10°08.72′ W, collected on 20 November 2009 by MAR-ECO #36066 (4120 m). MNRJ 8181 (1 specimen); locality: Ak. Ioffe Cruise 29, Shirshov st. 2184–5, Superestação 7, Sta. 201, series #1030, Mid-Atlantic Ridge, 29°27.12′ S 10°08.72′ W, collected on 20 November 2009 by MAR-ECO #36038 (4120 m).

Material examined: Bolocera kerguelensis: AMNH 4653 (5 specimens); locality: ANT XIX/5 Cruise, LAMPOS Program, RV Polastern, Sta. 61/150, Burdwood/Namuncurá Bank, 54°30.22′ S 56°08.20′ W, collected on 6 April 2002 by E. Rodríguez (286 m). AMNH 4912 (1 specimen); locality: ANT XXI/2 Cruise, BENDEX Program, RV Polastern, Sta. PS65/109-1, Antarctica, North Kapp Norvegia, 70°47.88′ S 11°21.56′ W, collected on 10 December 2003 by E. Rodríguez (1488 m).

External anatomy (fig. 7): Pedal disc well developed, circular, with well-marked limbus, 49–62 mm in diameter in preserved specimens. Column funnel shaped, short, cylindrical, smooth, not divided into regions, much wider than pedal disc; margin not tentaculate. Column beige, 45–49 mm in diameter and 35–44 mm in length in preserved specimens. Oral disc circular, wide, nonretractile, same color as column, with large central mouth with two visible siphonoglyphs; specimens with everted actinopharynx due to sampling process (fig. 7D); 44–62 mm in diameter in preserved specimens. Tentacles deciduous with basal marginal endodermal sphincter, numerous, smooth, thick, with longitudinal ridges, 170–182 in 6 cycles (6+6+12+24+48+n) in most of oral disc (fig. 7D); many tentacles autotomized and detached from oral disc of preserved specimens, their absence marked by holes in oral disc (fig. 7D). Inner and outer tentacles of similar or dissimilar size due to regeneration (fig. 7D); longest tentacle up to 50 mm in preserved specimens.

Internal anatomy and histology (fig. 7): Body wall thickness uniform throughout column: gastrodermis (316–537 µm), mesoglea (314–595 µm), and epidermis (287–542 µm) (fig. 7B). Marginal sphincter endodermal musculature diffuse (fig. 7C). Longitudinal musculature of tentacles ectodermal.

Mesenteries in five cycles (6+6+12+24+n = 90–93) spanning most of body length (fig. 7E, F): mesenteries of first and second cycles perfect, fertile, except for two pairs of sterile directives (fig. 7E); each pair of directives associated with one siphonoglyph; third cycle mostly imperfect, sometimes perfect, fertile (fig. 7F, G); fourth and fifth cycles imperfect (fig. 7G, H and fig. 7G, I, J, respectively). Mesenteries of first to fourth cycles with filaments (fig. 7F, G); those of fifth cycle without filaments (fig. 7F, H). Same number of mesenteries distally and proximally. All specimens collected in November males; major axis of spermatic cysts 113–405 µm (fig. 7G, H). Species inferred gonochoric. Retractors of all mesenteries strong, diffuse (fig. 7F–H, I); parietobasilar musculature in all mesenteries (fig. 7F–L), but particularly strong and well developed with free mesogleal flap in mesenteries of first to fourth cycles (fig. 7F, G, K); mesenteries of fifth cycle with weak parietobasilar musculature (fig. 7K).

Cnidom (fig. 8): Spirocysts, basitrichs, b-mastigophores, p-mastigophores A. See figure 8 and table 3 for size and distribution.

Distribution and natural history: The two specimens of Bolocera kerguelensis were collected in the area west of the Mid-Atlantic Ridge in the South Atlantic at 4120 m. The specimens were not attached to any solid substrate, which suggests they might rest loosely on the sediment as noted by other authors (Dunn and Bakus, 1977; Riemann-Zürneck, 1979). Our new records extend the geographic range of the species—which is widespread in the Southern Ocean (plus doubtful records in the South African coast: see Rodríguez and López-González, 2013) and on both sides of South America (Dunn, 1983; Riemann-Zürneck, 1986; Rodríguez and López-González, 2013)—to include the area surrounding the SMAR region above the 35° S parallel (fig. 1). The closest previous record to the Mid-Atlantic Ridge is from the area around the Traversay Islands (Dunn, 1983) but at a much shallower depth (1532–1590 m). We also extend slightly the bathymetric range of this eurybathic species known from the continental shelf to bathyal depths in the Antarctic and sub-Antarctic regions (Rodríguez et al., 2007; Rodríguez and López-González, 2013) from 45–3947 m to 45–4120 m. These new records represent a third instance of a deep-sea anemone found in Antarctica and sub-Antarctica whose geographic range extends beyond the Southern Ocean, the others being Galatheanthemum profundale Carlgren, 1956, and Liponema multiporum Hertwig, 1882 (see Rodríguez et al., 2007).

Remarks: The differentiation of species in the genus Bolocera based on morphology or cnidae is difficult, particularly for species recorded for the South Atlantic (Rodríguez and López-González, 2013). The circumscription of the genus Bolocera in the South Atlantic and Antarctic region has varied from two species—either B. kerguelensis and B. tuediae occidua (Riemann-Zürneck, 1980) or B. kerguelensis and B. paucicornis Dunn, 1983—to only one, B. tuediae kerguelensis (Riemann-Zürneck, 1986). However, because Rodríguez and López-González (2013) found inconsistencies in the morphological and cnidae characters used by Riemann-Zürneck (1980) and Dunn (1983) to differentiate Bolocera species in the Southern Ocean, the authors synonymized all species under B. kerguelensis until further studies (Rodríguez and López-González, 2013). For this reason, until a thorough morphological and molecular revision of the genus is carried out, we identify our specimens as B. kerguelensis as the morphology of our specimens generally agree with previous descriptions of that species (e.g., Riemann-Zürneck, 1980; Rodríguez and López-González, 2013). One exception is the fertility of the mesenteries of the fourth cycle, which was previously described as sterile (Rodríguez and López-González, 2013), but they were fertile in our specimens (fig. 7F, G). Similarly, the cnidae of specimens examined in this study agrees with the cnidom given by Rodríguez and López-González (2013) for B. kerguelensis from Antarctica, except for our finding of p-mastigophores A in the column (fig. 8C) and nematocysts we identified as b-mastigophores in the filament of our specimens (fig. 8L), both of which have never been described in B. kerguelensis. It is possible these two nematocysts were not found in previous studies due to their scarcity, particularly of the p-mastigophores A of the column, but their presence has been confirmed in histological sections. The b-mastigophores found in the filaments are similar to those found in other actiniids (e.g., Epiactis Verrill, 1869a, Glyphoperidium Roule, 1909, Isosicyonis Carlgren, 1927).

Diagnosis (modified from Carlgren, 1949; modifications in bold): Actiniidae with well-developed pedal disc. Column smooth, divisible into scapus and scapulus. Scapus with easily deciduous cuticle. Margin with perforated pseudoacrorhagi with basitrichs. Endodermal marginal sphincter well developed, circumscribed. Tentacles short, hexamerously arranged, inner longer than outer ones. Two siphonoglyphs. Approximately same number of mesenteries proximally and distally. Retractors strong, diffuse. Parietobasilar and basilar musculature distinct. Mesenteries of first and second cycle sterile. Cnidom: spirocysts, basitrichs, p-mastigophores A.

Types species: Isotealia antarctica Carlgren, 1899, by original designation.

Valid species: Isotealia antarctica; I. dubia (Wassilieff, 1908) (Fautin, 2016).

Material: MNRJ 8162 (2 specimens); locality: Ak. Ioffe Cruise 29, Shirshov St. 2184-5, Superestação 2, series #1040, Sta. 201, Mid-Atlantic Ridge, 32°50.15′ S 14°07.0′ W, collected on 22 November 2009 by MAR-ECO #38152 (1401 m).

Material examined: Isotealia cf. antarctica USNM 42671 (1 specimen); locality: R/V Albatross, Sta. 2767, South Atlantic Ocean, Blanca Bay, 40°03′ S 58°55.99′ W, collected on 13 January 1888 by United States Fish Commission (95 m).

External anatomy (fig. 9): Pedal disc flat, circular, adherent, slightly broader than column, with visible mesenteries insertions as dark lines; up to 84 mm in diameter in preserved specimens (fig. 9A). Column cylindrical, smooth, divisible into scapus and scapulus (fig. 9A). Margin with 48 pseudoacrorhagi with bastrichs; small fosse (fig. 9B). Column beige in preserved specimens with deciduous cuticle covering most of scapus, including pseudoacrorhagi (fig. 9A, B). Column up to 47 mm in length and 66 mm in diameter in preserved specimens. Oral disc partly contracted in preserved specimens, narrower than column diameter, with central, large mouth and short tentacles visible (fig. 9A); oral disc 33 mm in diameter in preserved specimens (fig. 9A). Tentacles 170–182, smooth, short, beige or olive green, with no markings (fig. 9B), in 6 cycles (6+6+12+24+48+[74–86)]) in outer half of oral disc (fig. 9A).

Internal anatomy and histology (fig. 9): Marginal sphincter musculature endodermal, circumscribed (fig. 9C). Actinopharynx short, longitudinally sulcated throughout. Longitudinal musculature of tentacles ectodermal (fig. 9D). Mesenteries hexamerously arranged in five cycles (6+6+12+24+[37–43] = 85–91 pairs), more mesenteries proximally than distally (fig. 9E, F): first and second cycles perfect, sterile, including two pairs of directives, each associated to one siphonoglyph; third cycle perfect, fertile, with filaments (fig. 9G, H); fourth cycle imperfect, fertile, with filaments (figs. 9G, I); fifth cycle imperfect, sterile, without filaments (figs. 9J, K). Retractors of first to third cycles strong, diffuse (figs. 9G–I) and parietobasilar musculature well developed, with thick mesogleal flap (figs. 9L, M); mesenteries of fourth and fifth cycles with weak retractors and parietobasilar musculature no developed (figs. 9J, K). Basilar musculature strong. All examined specimens collected in November female (figs. 9G–I, N), major axis of oocytes 117–919 µm in diameter. Species inferred gonochoric.

Cnidom (fig. 10): Spirocysts, basitrichs, p-mastigophores A. See figure 10 and table 4 for size and distribution.

Distribution and natural history: Isotealia antarctica is currently an Antarctic and sub-Antarctic species found off the coast of Argentina and Chile (McMurrich, 1893; Carlgren, 1959; Häusserman and Försterra, 2005) and as far north as the Rio de La Plata (Riemann-Zürneck, 1980). Rieman-Zürneck (1980) concluded that I. antarctica inhabits a corridor parallel to the continental shelf between 34° S–50° S due to a low tolerance of temperature fluctuations. More recently, Rodríguez and López-González (2013) extended the geographic range of I. antarctica to Bouvet Island, in the southeast of Antarctica. Here we further extend the range of I. antarctica in the South Atlantic to the area around the south Mid-Atlantic Ridge (fig. 1). We also extend the bathymetric range of I. antarctica, which has been found in the continental shelf and bathyal depths from 25–600 m (Rodríguez and López-González, 2013) to 1401 m. Our specimens were not attached to any substrate, unlike the specimens collected on solitary corals or snail shells by Riemann-Zürneck (1980).

Remarks: According to Riemann-Zürneck (1980), most specimens identified as I. antarctica (Carlgren, 1927) were poorly preserved and thus their distribution in Antarctica, Patagonia, and Chile needs confirmation. Records of I. antarctica in ecological studies in the Ross Sea (e.g., Dayton et al., 1974; Amsler et al., 1999) also need to be verified (Rodríguez and López-González, 2013). Furthermore, the specimen identified by Pax (1922) in the South Shetland Islands was identified by Carlgren (1927) as Telianthus inciertus Carlgren, 1927. The specimens of I. antarctica examined in this study agree morphologically with previous descriptions for the species (e.g., Carlgren, 1927; Riemann-Zürneck, 1980; Rodríguez and López-González, 2013). Our specimens were all female with large oocytes, even larger than those reported by Riemann-Zürneck (1980), i.e., 800 µm, but unlike Riemann-Zürneck (1980), we found no gametogenic tissue on pairs of the fifth cycle. In addition, we did not find some pairs of fourth cycle perfect as did Rodríguez and López-González (2013). Our cnidae measurements agree with those given by Riemann-Zürneck (1980), except for our finding of p-mastigophores A in the column of our specimens, which were not found by Riemann-Zürneck (1980) or Rodríguez and López-González (2013) in Antarctic specimens. On the other hand, the small basitrichs in the tentacles and b-mastigophores in the filaments found by Rodríguez and López-González (2013) were not found in our specimens. It is possible these differences are due to variability between populations and influence of local conditions (Rodríguez and López-González, 2013).

Diagnosis (modified from Carlgren, 1949; modifications in bold): Actinoscyphiidae with pedal disc never flat, sometimes very small, often on worm tubes or sponge spicules. Column thick to very thick, smooth, of gelatinous consistency. Tentacles in two cycles at margin of wide oral disc; tentacles with mesogleal basal aboral thickenings. Oral disc wide, lobed, sometimes bilobed. Longitudinal muscles of tentacles and radial muscles of oral disc ectodermal, sometimes mesoectodermal. Mesogleal sphincter musculature weak. Siphonoglyphs well developed. Mesenteries more numerous than tentacles. Six pairs of perfect and sterile mesenteries with diffuse retractors. All mesenteries thin, delicate, with weak, diffuse retractors. Cnidom: spirocysts, basitrichs, p-mastigophores B1, and holotrichs.

Type species: Actinernus saginata Verrill, 1882, by original designation.

Valid species: Actinoscyphia saginata; A. aurelia (Stephenson, 1918b); A. plebeia (McMurrich, 1893); A. groendyki Eash-Loucks and Fautin, 2012; (?) A. verrilli (Gravier, 1918) (Fautin, 2016).

Material: MNRJ 4223 (1 specimen); locality: REVIZEE Bahia 2, Sta. ZO522, sector 2, dredging 58, Southwestern Atlantic, Brazil, off the coast of Espirito Santo (ES), 21°15.22′ S 39°53.05′ W, collected on 8 July 2000 by R/V Thalassa (1694 m). MNRJ 4224 (1 specimen); locality: REVIZEE Bahia 2, Sta. ZO527, sector 1, dredging 33, Southwestern Atlantic, Brazil, off the coast of Espirito Santo (ES), 20°02.23′ S 39°23.62′ W, collected on 29 June 2000 by R/V Thalassa (1402 m). MNRJ 4226 (1 specimen); locality: REVIZEE Bahia 2, Sta. EO525, sector 1, dredging 31, Southwestern Atlantic, Brazil, off the coast of Espirito Santo (ES), 20°10.42′ S 38°40.42′ W, collected on 28 June 2000 by R/V Thalassa (1639 m).

Material examined: Actinoscyphia saginata: ZMUC ANT-000014 (1 specimen; syntype); locality: Ingolf Expedition, Sta. ING032, Arctic Ocean, Davis Strait, 66°35.0′S 56°38.0′W, collected 11 July 1896 (599 m). USNM 78477 (3 specimens); locality: Northern Gulf of Mexico Continental Slope Expedition (NGOMCS), Cruise, IV, Sta. WC-9, R/V Citation, North Atlantic Ocean, northern Gulf of Mexico off Louisiana, 27°42.79′ S 91°15.28′ W, collected on 23 May 1985 (695–807 m). USNM 079597 (1 specimen); locality: northern Gulf of Mexico Continental Slope Expedition (NGOMCS), Cruise, III, Sta. C11, R/V Gyre, northern Gulf of Mexico off Louisiana, 27°13.69′ S 89°36.80′ W, collected on 8 December 1984 (2063–2085 m). Actinoscyphia plebeia: AMNH 4080 (14 specimens); locality: ANT XIX/3 Cruise, ANDEEP I Program, R/V Polarstern, Sta. PS61/114-10, Southern Ocean, Drake Passage, 61°43.7′ S 60°42.62′ W, collected on 19 February 2002 by Mercedes Conradi (2853–2856 m).

External anatomy (fig. 11): Animal irregularly shaped (fig. 11A). Pedal disc well developed, elongate, perpendicular to directive axis, tubular, wrapped around cylindrical substrate, with golden-brown chitinous material (fig. 11A, B); 88–142 mm in diameter in preserved specimens. Column irregularly shaped, not divisible into regions, stiff, smooth, mostly without epidermis and light-pink mesoglea exposed (fig. 11A); 19–57 mm in length and 52–92 mm in preserved specimens. Brown-red epidermis in parts of column (fig. 11A) and oral disc. Oral disc wide, irregularly shaped, folding on itself, but not bilobed (fig. 11A), with large central mouth; 34–62 mm in diameter in preserved specimens. Tentacles brown-red, slender, long, marginal, with beige, mesogleal basal aboral thickenings (fig. 11A); 140–152 in two marginal cycles (fig. 11A); outer tentacles longer than inner ones, longest tentacle up to 25 mm in preserved specimens.

Internal anatomy and histology (fig. 11): Body wall thick throughout column with mesoglea (306–526 µm) much thicker than gastrodermis (60–172 µm), and epidermis (69–237 µm); mesoglea less thick proximally. Marginal sphincter musculature mesogleal, weak and diffuse without tendency for stratification, wider marginally and thinner proximally closer to gastrodermis (fig. 11C): all alveoli nonpigmented, larger and reticular distally (fig. 11D), smaller and scattered proximally (fig. 11E). Longitudinal musculature of tentacles ectodermal but less developed in aboral side (fig. 11F); mesogleal basal aboral thickenings in tentacles (fig. 11G).

Mesenteries hexamerously arranged in five cycles (6+6+12+24+n = 72–80 pairs) on entire body length: mesenteries of first and second cycles perfect proximally (fig. 11H), including two pairs of directives each associated to one siphonoglyph. First cycle sterile; second to third cycles imperfect, fertile, with filaments only proximally (fig. 11H); fourth cycle imperfect, sterile, with filaments (fig. 11I); fifth cycle imperfect, sterile, without filaments (fig. 11J). Same number of mesenteries distally and proximally. Mesenteries thin, with some sections with mesogleal thickenings (fig. 11B, H); retractors diffuse slightly more developed distally (fig. 11I, L); well-developed parietobasilar musculature in all mesenteries (fig. 11M) less developed in mesenteries of fifth cycle (fig. 11N). All specimens collected in June and July males; major axis of spermatic cysts 76–238 µm (fig. 11K). Species inferred gonochoric.

Cnidom (fig. 12): Spirocysts, basitrichs, p-mastigophores B1, and holotrichs. Some nematocysts found in the actinopharynx (fig. 12M) and filament (fig. 12P) are likely the result of contamination by feeding. See figure 12 and table 5 for size and distribution.

Distribution and natural history: Actinoscyphia saginata was originally described from the Atlantic coast of the United States off New England (968 m) (Verrill, 1882). The species is also known from the Atlantic coast of France (2108–2177 m) and Morocco (1341–1394 m) (Riemann-Zürneck, 1978). Our specimens extend the geographic distribution of A. saginata to the South Atlantic off the coast of Espírito Santo, Brazil and falls within the known bathymetry for the species (1402–1694 m).

Remarks: The genus Actinoscyphia contains five valid species that are easily recognized by their venus flytraplike morphology: large bilobed oral discs and marginal tentacles arranged in two cycles forming a concave surface. The morphology of the body and oral disc enables these anemones to position themselves within the current and and feed on particles upstream. Although the term “venus flytrap anemone” was originally used to refer to species in genus Actinoscyphia, some hormathiids in genera Phelliactis Simon, 1892, and Paraphelliactis Carlgren, 1928b, as well as members of Amphianthus Hertwig, 1882, also have bilobed oral discs with marginal tentacles resembling to the ones seen in actinoscyphiids. The similarity in the venus flytraplike morphology in all these genera has led to misidentification of the many images of venus flytrap anemones attributed to Actinoscyphia, when in fact they refer to other families and genera. In any case, species of Actinoscyphia are mainly distributed in the North Atlantic (A. saginata, A. aurelia) or northeastern Pacific (A. groendyki) with only one species known from the sub-Antarctic region of the Pacific and Atlantic region of Antarctica (A. plebeia: Rodríguez and López-González, 2013) as well as off the South African coast (Laird and Griffiths, 2016). Though A. groendyki was originally described based on material collected in the northeastern Pacific and specimens of A. plebeia from the Southern Ocean examined by Fautin (1984), we agree with Rodríguez and López-González (2013) and restrict the distribution of A. groendyki to the northeastern Pacific and of A. plebeia to the Southern Ocean.

Actinoscyphia species are differentiated based on their external anatomy (size and number of tentacles and its mesogleal basal aboral thickenings; pedal disc shape and size; oral disc shape and coloration), internal anatomy (number of perfect pairs of mesenteries; number of cycles of mesenteries, fertility), microanatomy (thickness of mesoglea; development and morphology of marginal sphincter musculature; pigmentation of alveoli in sphincter musculature) and cnidae (presence of holotrichs in tentacles, p-mastigophores B1 in column and tentacles, etc.). For a dichotomous key of Actinoscyphia species see Eash-Loucks and Fautin (2012). The Brazilian specimens of A. saginata agree well with previous descriptions of the species (e.g., Stephenson, 1918b; Riemann-Zürneck, 1978) and can be identified unequivocally by a combination of characters related to its shape (large, shapeless body), pedal disc (tubular shaped and attached to solid substrates), oral disc (irregular but not bilobed), tentacles (relatively long with mesogleal basal aboral thickenings), coloration (dark-brown tentacles, oral disc, and pharynx), sphincter musculature (nonpigmented alveoli), and cnidae (p-mastigophores B1 in column). The cnidae of the Brazilian specimens of A. saginata closely agrees with the cnidom provided by Riemann-Zürneck (1978) for the species, with a few minor differences: we found in our specimens many spirocysts as well as few holotrichs in the column, no small basitrichs in the tentacles, and longer basitrichs in filaments. These differences, however, do not prevent the identification of Brazilian specimens as A. saginata.

Diagnosis (modified from Carlgren, 1949; modifications in bold): Amphianthidae with broad pedal disc, often elongated in transversal or sagittal plane. Column smooth or with small mesogleal papillae in longitudinal rows distally. Cinclides as a rule only on directive endoceles, few in number (1–3 or a few more?); external opening often on papillae; cinclides sometimes indistinct or absent. Mesogleal marginal sphincter musculature strong. Tentacles robust, always fewer than mesenteries at limbus, sometimes with mesogleal basal aboral thickenings. Longitudinal muscles of tentacles and radial musculature of oral disc ectodermal. One to three siphonoglyphs. Pairs of perfect mesenteries at least six, often irregular. One to three pairs of directives. Stronger mesenteries fertile except sometimes the directives. Retractors diffuse, usually fairly weak. Acontia well developed. Cnidom: spirocysts, basitrichs, p-mastigophores B1, and holotrichs.

Type species: Amphianthus bathybium Hertwig, 1882, by original designation.

Valid species: Amphianthus armatus Carlgren, 1928a; A. bathybium; A. brunneus (Pax, 1909); A. californicus Carlgren, 1936; A. capensis Carlgren, 1928a; A. caribaeus (Verrill, 1899); A. dohrnii (Koch, 1878); A. ingolfi Carlgren, 1942; A. islandicus Carlgren, 1942; A. lacteus (McMurrich, 1893); A. laevis Carlgren, 1938; A. margaritaceus (Danielssen, 1890); A. michaelsarsi Carlgren, 1934; A. minutus (Hertwig, 1882); A. mirabilis (Verrill, 1879); A. mopseae (Danielssen, 1890); A. natalensis Carlgren, 1938; A. nitidus (Verrill, 1899); A. norvegicus Carlgren, 1942; A. radiatus Carlgren, 1928a; A. rosaceus Wassilieff, 1908; A. sanctaehelenae Carlgren, 1941a; A. valdiviae Carlgren, 1928a; A. verruculatus Carlgren, 1942 (Fautin, 2016).

Material: MNRJ 8273 (4 specimens); locality: Projeto PIR 2, Sta. Fasciologia Norte PIR-2, Amostrador Box core Zona 235, southwestern Atlantic, Brazil, off the coast of São Paulo, 24°49.45′ S, 44°23.02′ W, collected on 16 December 2008 by R/V F. Odyssey (no depth data). MNRJ 8284 (4 specimens); locality: Projeto PIR 2, Sta. Fasciologia Sul PIR-2, Amostrador Box core Zona 235, southwestern Atlantic, Brazil, off the coast of São Paulo, 24°55.37′ S 44°27.23′ W, collected on 10 December 2008 by R/V F. Odyssey (735 m).

Material examined: Amphianthus michaelsarsi: MZB 39191 (8 specimens, syntypes); locality: Michael Sars Expedition 1910, St. 53, North Atlantic Ocean, 34°59.0′ N 33°01.0′ W, collected 8 June 1920 by O. Carlgren (2615 m).

External anatomy (fig. 13): Pedal disc flat, irregularly shaped, highly adherent, broader than column diameter, 16–21 mm in diameter in preserved specimens (fig. 13A). Column cylindrical, smooth not visibly divisible into regions (fig. 13A); cinclides absent. Column white in preservation with beige, thin, deciduous cuticle (fig. 13A). Column 12–21 mm in diameter and 12–15 mm in length. Small fosse. Oral disc circular, as wide or slightly wider than column with central, with large mouth (fig. 13B). Oral disc diameter 10–11 mm in preserved specimens. Tentacles 90–94, smooth, short, beige same color as column, with no markings, in 5 cycles (6+4+10+20+n) in outer half of oral disc in preserved specimens (fig. 13B); inner longer than outer ones with longest tentacle up to 25 mm in preserved specimens.

Internal anatomy and histology (fig. 13): Body-wall thickness varying along column: all three body layers thicker in scapulus than scapus (fig. 13C). Sphincter long, narrow, with mesogleal musculature (fig. 13C); fibers in most of mesoglea distally, thinner proximally (fig. 13C). Longitudinal musculature of tentacles ectodermal (fig. 13D); no mesogleal basal aboral thickening on tentacles. Longitudinal musculature of oral disc ectodermal (fig. 13E). Actinopharynx very short, longitudinally sulcated throughout (fig. 13F, G). Specimens with two weakly differentiated siphonoglyphs (fig. 13G).

Mesenteries decamerous, in four cycles (6+4+10+20 = 40 pairs): first and second cycles perfect, including one pair of directives associated to one siphonoglyph (fig. 13F, G); third and fourth cycles imperfect (fig. 13G). All mesenteries of first to third cycles, including directives, with filaments and acontia (fig. 13G); those of fourth cycle without filaments or acontia (fig. 13G–I). Mesenteries more numerous proximally. Retractors of first and second cycles weakly developed, diffuse, restricted to distal half of mesentery (figs. 13H, J); those of third and fourth cycles weakly diffuse (fig. 13H). Acontia very abundant on mesenteries of first and second cycles (fig. 13H, I). Parietobasilar musculature small, weak in all mesenteries, including stronger ones (fig. 13K). Basilar musculature of mesenteries weak (not shown). Gametogenic tissue on all mesenteries except in directives and those of forth cycle (fig. 13G). Eggs/larvae in oral disc and tentacles (fig. 13E).

Cnidom (fig. 14): Spirocysts, basitrichs, b-mastigophores, p-mastigophores B1, p-mastigophores B1, and holotrichs. Some p-mastigophores B1 are likely immature capsules (fig. 14F, L, P). See figure 14 and table 6 for size and distribution.

Distribution and natural history: Specimens were collected attached to skeletons of the scleractinian Solenosmilia variabilis Duncan, 1873 (fig. 13A) in the Santos Basin off the coast of São Paulo, Brazil at 735 m. Amphianthus lacteus is known from its type locality on the eastern Pacific (Chile) and from specimens identified as A. aff. lacteus reported from several localities off the coast of Argentina from around Burdwood Bank to Rio de La Plata (Riemann-Zürneck, 1986). The Brazilian specimens examined here extend the geographic range of A. lacteus further north across the Rio de La Plata and fall into the known bathymetric range of the species (398–821 m).

Remarks. The presence of acontia with only basitrichs and the 12 perfect pairs of mesenteries unequivocally place our specimens within Amphianthidae (Rodríguez et al., 2012). In addition, our specimens also exhibit a modified, grasping pedal disc, which is diagnostic for the group Graspina sensu Rodríguez et al. (2012) (i.e., Amphianthidae plus Actinoscyphiidae Stephenson, 1920). The morphological distinction between Amphianthus and Stephanauge Verrill, 1899, is difficult, but the abundance of acontia in our specimens (fig. 13I) identifies them as Amphianthus rather than Stephanauge, because Stephanauge species have few to no acontia (Carlgren, 1949). Even harder is make definitive identifications of the 24 valid species of Amphianthus (Fautin, 2016), which led Riemann-Zürneck (1986) to suggest that identification of the species of Amphianthus from Argentina required a revision of the entire genus. We agree with Riemann-Zürneck (1986) in that specific identification within Amphianthus is rather difficult, but using the combination of the wide, circular pedal disc of the Brazilian specimens, which is not elongated in the sagittal plane as in many other Amphianthus, the decamerism of our specimens (rare within the genus), the lack of tubercles on the distal column and conspicuous cinclides, we can identify our specimens as A. lacteus. Our specimens agree in all morphological details with those described by McMurrich (1893). We provide the cnidae of the species for the first time, which was not given by McMurrich (1893). We found several eggs/larvae in the oral disc and tentacles of our specimens (fig. 13E), a feature also found in other species with similar wide distribution in the SWA (e.g., Paractis laevis (Carlgren, 1899), Antholoba achates (Drayton in Dana, 1846).

Diagnosis (modified from Zelnio et al., 2009; modifications in bold): Hormathiidae with well-developed pedal disc. Body elongated, without cinclides, divisible into scapus and scapulus; scapus with cuticle and tubercles distally, 12 or 24 short rows of conspicuous tubercles. Scapulus longitudinally sulcated. Very strong mesogleal marginal sphincter. Tentacles hexamerously arranged. Longitudinal muscles of tentacles and radial muscles of oral disc ectodermal. Six pairs of perfect mesenteries. Mesenteries of oldest cycles, including directives, fertile, with filaments and acontia. Mesenteries of youngest full cycle and of any subsequent partial cycles present only proximally, sterile, without filaments or acontia. Same number or fewer mesenteries at midcolumn than distally or proximally. Below actinopharynx, inner part of nondirective mesenteries may curve toward exoceles. Perfect and stronger imperfect mesenteries with diffuse retractors; retractors usually fairly close to body wall. Parietobasilar muscles weak. Acontia well developed. Cnidom: Spirocysts, basitrichs, p-mastigophores A, and p-mastigophores B1.

Type species: Actinauge nodosa var. coronata Verrill, 1883, by original designation.

Valid species: Chondrophellia africana Carlgren, 1928a; C. coronata; and C. orangina Zelnio et al., 2009.

Material: MNRJ 5714 (1 specimen); locality: OceanProf II-BC Norte-Cenpes/UFRJ, dredging #16-1, N/RB Astro Garoupa, southwestern Atlantic, Brazil, off the coast of Rio de Janeiro (RJ), 23°27.73′ S–22°15.07′ S 39°59.0′ W–39°55.72′ W, collected on 22 August 2003 by ? (1059–1110 m). MNRJ 5687 (3 specimens); locality: Projeto OceanProf II-BC Sul-Cenpes/UFRJ, N/RB Astro Garoupa, southwestern Atlantic, Brazil, off the coast of Rio de Janeiro (RJ), 22°28.65′ S 40°04.30′ W/22°29.7′ S 40°05.1′ W, collected on 25 August 2003 (1290–1325 m). MNRJ 6918 (1 specimens); locality: southwestern Atlantic, Brazil, off the coast of Rio de Janeiro (RJ), Projeto OceanProf I-BC Norte-Cenpes/UFRJ, dredging #15, N/RB Astro Garoupa, 22°01.98′ S–21°52.22′ S 39°49.87′ W–40°02.28′ W, collected on 14 February 2003 (1620–1598 m). MNRJ 6664 (2 specimens); locality: Projeto Caracterização de corais de água profunda, Mergulho 2, Área 32, Banco 85N, Dop. 8, ROV Toisa Conqueror, southwestern Atlantic, Brazil, off the coast of Rio de Janeiro (RJ), 22°25.73′ S 39°57.73′ W, collected on 23 July 2005 (1059–1110 m).

External anatomy (fig. 15): Pedal disc flat, circular, highly adherent, equal to or broader than column, insertion of mesenteries visible when exposed, 3–13 mm in diameter in preserved specimens (fig. 15B). Column cylindrical, mostly covered by small tubercles (fig. 15A) in proximal and midcolumn, with a distal crown of 12 larger tubercles above which 12 smaller tubercles are (fig. 15B, C); column divided into long scapus and short scapulus with longitudinal ridges (fig. 15C). Column with thick, deciduous cuticle, highly adherent in some preserved specimens (fig. 15A) or entirely missing in others (fig. 15A–C). Margin of scapulus not tentaculate (fig. 15C). Cinclides absent. Column white in preserved specimens with mesenterial insertions visible as white lines, particularly in proximal column and limbus without cuticle (fig. 15B). Column 9–25 mm in length and 5–18 mm in diameter in preserved specimens. Oral disc circular, small, as wide or slightly narrower than column, mostly retracted in preserved specimens (fig. 15C). Central, small mouth. Oral disc diameter 1–6 mm in preserved specimens (fig. 15B, C). Tentacles up to 96, smooth, short, slender, and pointed, in five cycles (6+6+12+24+n) in preserved specimens. Tentacles with no markings and translucent beige in preserved specimens (fig. 15C). Longest tentacle up to 3 mm in preserved specimens.

Internal anatomy and histology (fig. 15): Body long and narrow in preserved specimens (fig. 15A, B) with wall thickness varying along column: mesoglea thicker in scapulus than in scapus, whereas epidermis is thicker in scapus than in scapulus (fig. 15D, E). Marginal sphincter long, with mesogleal musculature (fig. 15E); fibers in most of mesoglea distally (fig. 15E); alveolar proximally with tendency for reticulation elsewhere (fig. 15F). Longitudinal musculature of tentacles ectodermal (fig. 15G). Actinopharynx up to 8 mm in length, approximately one third of column's length; longitudinally sulcated throughout (fig. 15H, I); with thick mesoglea (fig. 15J, I). Specimens with two weakly differentiated siphonoglyphs (fig. 15H, I) with thin gastrodermis and mesoglea, but glandular epidermis as in actinopharynx.

Mesenteries hexamerously arranged in four cycles (6+6+12+24 = 48): first cycle perfect, including two pairs of directives, each associated to one siphonoglyph (fig. 15I); second and third cycles imperfect (fig. 15I). All mesenteries of first and second cycles, including directives, fertile and with filaments (fig. 15J–L, N); those of third cycle sterile and without filaments (fig. 15M). A fourth cycle of imperfect, sterile mesenteries only proximally; insertion of mesenteries visible on limbus (fig. 15B). More mesenteries proximally than distally (fig. 15B). All fertile specimens female, collected in July; major axis of oocytes up to 72 µm in diameter (fig. 15N). Species inferred gonochoric. Retractors of first and second cycles well developed, diffuse (fig. 15J–L); those of third cycle diffuse (fig. 15J, M). Parietobasilar musculature small, weak in all mesenteries (fig. 15K–M). Basilar musculature of mesenteries weak (not shown).

Cnidom (fig. 16): Spirocysts, basitrichs, p-mastigophores A, and p-mastigophores B1. The scyphozoanlike nematocyst (fig. 16L) found in the filament of this species is likely the result of contamination by feeding. See figure 16 and table 7 for size and distribution.

Distribution and natural history: Specimens of Chondrophellia coronata were collected off the coast of Rio de Janeiro state close to the Campos Basin in Brazil. Some of these specimens were collected attached to pieces of coral skeleton. Chondrophellia coronata is widely distributed in the North Atlantic (Carlgren, 1942; Molodtsova et al., 2008) and Gulf of Mexico (Ammons and Daly, 2008), but this is the first record of the species in the South Atlantic. The species has also been collected in the eastern Pacific off the coast of Chile (McMurrich, 1893) and off California (Doumenc and Van Präet, 1988). The Pacific records for C. coronata are somewhat questionable (Carlgren, 1942; Molodtsova et al., 2008; Zelnio et al., 2009). The specimens of C. coronata examined by Doumenc and Van Präet (1988) were collected in hydrothermal vents of the eastern Pacific and are similar to C. orangina collected off hydrothermal vents in the Lau Basin in the southwestern Pacific (Zelnio et al., 2009). The specimens of C. coronata off Brasil were collected between 1077–1620 m, which falls within the known range for the North Atlantic records (599–2448 m).

Remarks: The Brazilian specimens of Chondrophellia coronata agree closely with previous morphological descriptions of external and internal anatomy for the species (Carlgren, 1942). In particular, the distinctive combination of a distal corona of tubercles, the number of cycles of mesenteries (three spanning most of the column and a fourth only proximally), and the fertility of first and second cycles of mesenteries easily places our material within Chondrophellia. Types and size range of nematocysts from our specimens agree with those given by Carlgren (1942) and Zelnio et al. (2009) for C. coronata, except for the small basitrichs in the column and acontia found only in our specimens. These differences could be explained by the scarcity and difficulty of finding these small nematocysts, particularly in the acontia where the larger category is abundant. Our specimens are different from the C. coronata identified by Ammons and Daly (2008) in the Gulf of Mexico, which, given the asymmetrical morphology of the oral disc, resemble species of Phelliactis or Paraphelliactis.

The cnidae of Chondrophellia coronata from Brazil differs from the cnidae of C. africana Carlgren, 1928b, given by Zelnio et al. (2009). Our specimens are clearly different from C. orangina, based on the number of mesenteries (four cycles in C. coronata; five in C. orangina) and tentacles (five cycles in C. coronata; six in C. orangina), number of distal tubercles (12 rows in C. coronata; 24 in C. orangina), sphincter musculature (mostly reticular in C. coronata; alveolar in C. orangina), and other cnidae differences. Given the larger size of Chondrophellia specimens collected in the Pacific, it is possible that the Chilean specimens described by McMurrich (1893) and later examined by Carlgren (1942) as well as the C. coronata described by Doumenc and Van Präet (1988) for the eastern Pacific are similar to C. orangina from the Lau Basin in the western Pacific. A detailed revision of the mesentery arrangement of the material from Chile and California could help elucidate the specific identity of eastern Pacific Chondrophellia.

Diagnosis (modified from Carlgren, 1949; modification in bold): Hormathiidae with well-developed pedal disc often attached to shells. Column divisible into scapus and scapulus; scapus with tubercles sometimes on longitudinal rows, more rarely in coronal tubercles on distal scapus. Scapus usually with more or less strong cuticle. Marginal sphincter musculature mesogleal, strong. Tentacles not more than 96, exceptionally few more, without mesogleal basal aboral thickenings. Same number of mesenteries proximally and distally. Longitudinal muscles of tentacles and radial muscles of oral disc ectodermal; latter sometimes mesoectodermal. Two well-developed siphonoglyphs. Six pairs of perfect and sterile mesenteries. Retractors diffuse. Cnidom: spirocysts, basitrichs, p-mastigophores B1.

Type species: Hormathia margaritacea Gosse, 1859.

Valid species: Hormathia alba (Andres, 1881); H. andersoni Haddon, 1888; H. armata Rodríguez and López-González, 2001; H. castanea (McMurrich, 1904); H. coronata (Gosse, 1858); H. digitata (Müller, 1776); H. georgiana Carlgren, 1927, H. incubans (Gravier, 1918); H. indutus (Gravier, 1918); H. insignis (Stephenson, 1918a); H. josefi Zhiubikas, 1977; H. lacunifera (Stephenson, 1918a); H. marioni (Haddon, 1889); H. nodosa (Fabricius, 1780); H. pacifica Sanamyan et al., 2015; H. pectinata (Hertwig, 1882); H. spinosa (Hertwig, 1882) (Fautin, 2016).

Material: MNRJ 6759 (3 specimens); locality: Projeto Programa Obs, Bordo da Frota Arrendada Obs Doação de Carlos M.L. Silva, CF/V Kimpo Maru, southwestern Atlantic, Brazil, off the coast of Rio Grande do Sul (RS), 33°46.1′ S 52°00.03′ W, collected on 27 July 2002 (526 m).

Material examined: Hormathia armata: AMNH 4005 (1 specimen); locality: ANT XIX/3 Cruise, ANDEEP I Program, RV Polarstern, Sta. PS61/106–1, 61°38.02′ S 57°32.07′ W, Southern Ocean, Drake Passage, Antarctica, collected on 14 February 2002 (424–427 m). Hormathia lacunifera: AMNH 4106 (2 specimens); locality: ANT XIX/3 Cruise, ANDEEP I Program, RV Polarstern, Sta. PS61/049–1, 61°11.57′ S 54°42.99′ W, Southern Ocean, Antarctica, South Shetland Islands, Elephant Islands (272–306 m).

External anatomy (fig. 17): Body short and broad in preserved specimens, up to 52 mm in length and 58 mm in diameter (fig. 17A). Pedal disc flat, circular, adherent, 23 mm in diameter in preserved specimens (fig. 17A). Column cylindrical with deciduous cuticle (fig. 17A), often only between large tubercles (fig. 17A); tubercles smooth, distributed in entire column, regularly arranged (fig. 17A, H). Column divisible into scapus and scapulus; short capitulum not distinct, retracted into scapus in contracted preserved specimens (fig. 17A, B). Margin of capitulum tentaculate (fig. 17E). Column white in preserved specimens with brown cuticle (fig. 17A); 18 mm in length and 39 mm in diameter in preserved specimens. Oral disc circular, small, narrower than column in preserved specimens (fig. 17A). Oral disc contracted in all specimens, 10 mm in diameter in preserved specimens. Tentacles 92–96, short, thick, pointed, displaced to margin of oral disc.

Internal anatomy and histology (fig. 17): Body with wall thickness fairly uniform along column: epidermis and gastrodermis thinner than thick mesoglea (fig. 17E); limit between scapus and scapulus gradual (fig. 17E). Marginal sphincter musculature mesogleal, alveolar, long, narrow (fig. 17B, E); fibers in most of mesoglea, close to gastrodermis distally and scarce and narrow proximally (fig. 17B, E). Longitudinal musculature of tentacles ectodermal (fig. 17F); tentacles without mesogleal aboral thickenings (fig. 17G). Actinopharynx up to 20 mm in length, approximately one half of column's length; longitudinally sulcated throughout; with thick and highly glandular epidermis (not shown). Specimens with two differentiated siphonoglyphs (fig. 17H) with thin gastrodermis and epidermis and thick mesoglea.

Mesenteries hexamerously arranged in four cycles (6+6+12+24 = 48 pairs) on most of body length (fig. 17H, I): at actinopharynx-level first cycle perfect, including two pairs of directives, each associated with one siphonoglyph; remaining pairs of second to fourth cycles imperfect. All mesenteries with filaments; those of first to third cycles with acontia. All examined specimens sterile. Retractors of first to third cycles well developed, diffuse (fig. 17I), restricted to distal part of mesentery (fig. 17J, K); those of fourth cycle very weak (fig. 17L). Parietobasilar musculature weak in all mesenteries, (fig. 17I–L), stronger in mesenteries of fourth cycle (fig. 17K, L). Basilar musculature of mesenteries strong (not shown).

Cnidom (fig. 18): Spirocysts, basitrichs, p-mastigophores B1. See figure 18 and table 8 for size and distribution.

Distribution and natural history: Hormathia pectinata has been recorded from Chile and Argentina (Hertwig, 1882; McMurrich, 1893; Carlgren, 1959; Riemann-Zürneck, 1973) going as far north on the eastern coast of South America as the southern edge of the La Plata estuary off the coast of Mar del Plata. This species has a discontinuous distribution in the SWA (Riemann-Zürneck, 1986). Specimens of H. pectinata from this study were collected at a single site off the coast of Rio Grande do Sul in southern Brazil at 526 m. This new record extends the geographic range of H. pectinata north of La Plata River including the southern Brazilian coast, and fall within the shallower range of the species bathymetric distribution in bathyal (405–1220 m) rather than abyssal waters (2812–2925 m) (Rodríguez and López-González, 2001). Hormathia pectinata shows an overlapping geographic and bathymetric distribution only in its sub-Antarctic range with H. lacunifera, which is a circumpolar Southern Ocean species similarly distributed from continental shelf and bathyal depths. Hormathia spinosa (Hertwig, 1882), on the other hand, is found in sub-Antarctic region and Japan (Hertwig, 1882) whereas H. armata is known only from the Antarctic Peninsula and Weddell Sea at shallower continental waters (Rodríguez and López-González, 2013).

Remarks: The genus Hormathia is one of the most distinctive genera of Hormathiidae and is defined by characters that have all been found in our specimens: 6 pairs of perfect and sterile mesenteries, same number of mesenteries distally and proximally, column divisible into scapus and scapulus; scapus with tubercles and cuticle; no cinclides; 96 tentacles without aboral thickenings, and absence of cuplike pedal disc. Six species of Hormathia have been recorded in the Southern Hemisphere (Dunn, 1983; Rodríguez and López-González, 2013; Fautin, 2016) though only four might be valid (H. pectinata, H. lacunifera, H. spinosa, H. armata: Rodríguez and López-González, 2013). The anatomy and microanatomy of the individuals of H. pectinata examined in this study agrees with the description of Riemann-Zürneck (1973), including the number and cycles of tentacles and mesenteries. We observed the same thickening of the mesoglea in the retractors of mesenteries observed by Riemann-Zürneck (1973) (see fig. 17I–L). Unfortunately, our specimens were sterile, so we cannot comment on the fertility of the species. Though the comparative work of Riemann-Zürneck (1973) found that the taxonomic significance of the cnidon within the genus Hormathia is low, the size of basitrichs in the acontia is regarded as a distinctive character that differentiates species within the genus. Though the measurement of basitrichs in the acontia of our specimens is on the higher side of the range, it clearly identifies our specimens as H. pectinata and differentiates them from the remaining species of the genus in the southern Atlantic. Similar longer basitrichs in the acontia of specimens of H. pectinata were also found by Riemann-Zürneck (1973) in material from the coast of Argentina. The small size of individuals of H. pectinata found in Chile (type locality) might explain the particularly short basitrichs of the acontia in this material. Here, we confirm the presence of p-mastigophores B1 in relative abundance in the acontia of H. pectinata (fig. 18Q), which had been previously found by Riemann-Zürneck (1973) in H. pectinata from Argentina. This highly distinctive character further corroborates the identification of our specimens as H. pectinata and differentiates it from other species in the genus, and could explain the lack of a sister relationship between this species and other Hormathia spp. in all phylogenetic analyses to date (e.g., Gusmão and Daly, 2010; Rodríguez et al., 2012, 2014; Gusmão et al., 2019a, 2019b). It might also be possible that p-mastigophores have been overlooked in the acontia of other hormathiids and that further examination will reveal their presence in other genera or species in the family. The cnidom of our specimens agree generally with the one given by Riemann-Zürneck (1973) for H. pectinata, except that we found p-mastigophores B1 in the column and basitrichs in a larger category in the filaments, a difference that has been used to differentiate H. pectinata from H. armata and H. spinosa (E.R., personal obs.). It is possible that these large basitrichs in the filaments are the result of contamination from acontia as they overlap in size. In addition, although the p-mastigophores B1 found in the acontia of our specimens are of similar morphology (i.e., long and thin) to those described by Riemann-Zürneck (1973) for H. pectinata, the size of this cnida does not overlap, ours being slightly shorter than those given by Riemann-Zürneck (1973). Our measurements for H. pectinata closely agree with those given by Rodríguez and López-González (2001) for the holotype of H. pectinata and discrepancies, particularly the longer basitrichs in the scapus of the holotype, are probably due to the small number of capsules measured by Rodríguez and López-González (2001). Despite the known intraspecific variability in morphological characters within Hormathia (Riemann-Zürneck, 1994), including the development of tubercles (Rodríguez and López-González, 2013), the shape of the tubercles in our specimens, rounded or digitiformis (fig. 17A, H), aligning with the description of H. pectinata by McMurrich (1893), differentiates this species from H. armata and H. spinosa, both of which have piramidal tubercles. The corona of tubercles in our specimens is restricted to the distal scapus at the end of 12 longitudinal rows, which characterizes H. pectinata and differentiates it from H. armata and H. spinosa, whose tubercles are distributed in the entire scapus, though they are more prominent in the third most distal part of the scapus (E.R., personal obs.).

Diagnosis (modified from Carlgren, 1949; modifications in bold): Hormathiidae with well-developed pedal disc. Body often asymmetrical. Column divisible into scapus and scapulus; scapus with weaker or stronger cuticle and numerous irregularly arranged tubercles of varying sizes. Marginal sphincter mesogleal. Tentacles more than 100, fewer than mesenteries proximally, provided with strong mesogleal basal aboral thickenings; tentacles in two more or less distinct cycles. Longitudinal muscles of tentacles ectodermal. Oral disc wide, sometimes bilobed. Two well-developed siphonoglyphs. Six to eight pairs of perfect, sterile mesenteries. Single perfect supernumerary mesenteries often paired with imperfect ones. Retractors diffuse, rather weak. Parietobasilar musculature distinct but weak. Acontia well developed. Cnidom: spirocysts, basitrichs, p-mastigophores B1.

Type species: Phelliactis hertwigii Simon, 1892.

Valid species: Phelliactis algoaensis Carlgren, 1928a; P. americana Widersten, 1976; P. callicyclus Riemann-Zürneck, 1973; P. capensis Carlgren, 1938; P. capricornis Riemann-Zürneck, 1973; P. carlgreni Doumenc, 1975; P. coccinea (Stephenson, 1918b); P. crassa (Wassilieff, 1908); P. gigantea (Carlgren, 1941a); P. hertwigii; P. hydrothermala Sanamyan and Sanamyan, 2007; P. incerta Carlgren, 1934; P. japonica (Wassilieff, 1908); P. lophohelia Riemann-Zürneck, 1973; P. magna (Wassilieff, 1908); P. pelophila Riemann-Zürneck, 1973; P. pulchra (Stephenson, 1918b); P. robusta Carlgren, 1928b; P. siberutiensis Carlgren, 1928a; P. somaliensis Carlgren, 1928a; Phelliactis yapensis Li and Xu, 2016.

Material: MNRJ 4165 (1 specimen); locality: REVIZEE Bahia 2, R/V Thalassa, Sta. e0500, sector 1, arrest 6, southwestern Atlantic, Brazil, off the coast of Bahia, 13°22.95′ S 38°43.4′ W, collected on 8 June 2000 (394 m). MNRJ 4166 (3 specimens); locality: REVIZEE Bahia 2, R/V Thalassa, Sta. e0517, sector 1, arrest 6, southwestern Atlantic, Brazil, off the coast of Bahia, 13°24.55′ S 38°38.88′ W, collected on 19 June 2000 (750 m). MNRJ 4167 (4 specimens); locality: REVIZEE Bahia 2, R/V Thalassa, Sta. e0499, sector 1, arrest 5, southwestern Atlantic, Brazil, off the coast of Bahia, 13°36.77′ S 38°46.02′ W, collected on 8 June 2000 (761 m).

Material examined: Phelliactis robusta: ZMUC ANT-000014 (1 specimen; syntype); locality: Ingolf Expedition, Sta. ING032, Arctic Ocean, Davis Strait, 66°35.0′ N 56°38.0′ W, collected 11 July 1896 (599 m). Phelliactis americana: USNM 54323 (1 specimen; Holotype); locality: RV Delaware, North Atlantic Ocean, United States, off New Jersey, collected on 19 February 1963, ID by B. Widersten on 15 September 1975 (366 m). Phelliactis capricornis: ZMH C7547 (1 specimen; holotype); locality: Walther-Herwig Expedition, Sta. 85, Southwest Atlantic, Brazil, about 200 km off the State of São Paulo, 25°13.2′ S 44°33.0′ W (1200 m). Phelliactis incerta: MZB 39198 (1 specimen; holotype); locality: Michael Sars North Atlantic Deep-sea Expedition 1910, Sta. 23, Atlantic Ocean, near Strait of Gibraltar, 35°31.8′ S 7°07.2′ W (1215 m).

External anatomy (fig. 19): Preserved specimens 53–78 mm in length and 32–54 mm in diameter (fig. 19A). Pedal disc irregularly shaped, slightly broader than column, 32–88 mm in diameter in preserved specimens (fig. 19A). Column cylindrical, with large tubercles from proximal to distal column (fig. 19A); in some specimens tubercles larger in distal column (fig. 19B). Column divisible into long scapus and short capitulum (fig. 18A); capitulum smooth, visibly distinct in contracted preserved specimens (fig. 19B, C). Margin of capitulum tentaculate (fig. 19C). Column white or beige in preserved specimens, with deciduous cuticle remaining only in spaces between tubercles (fig. 19A). Column 53–78 mm in length and 32–54 mm in diameter in preserved specimens. Oral disc irregularly shaped, wider than column, bilobed (fig. 19A, B); 19–44 mm in diameter in preserved specimens. Tentacles 173–180, smooth, short, slender and pointed, in six cycles (6+6+12+24+48+n), displaced to margin of oral disc (fig. 19C). All tentacles of same size, white or beige in preserved specimens (fig. 19B, C); longest tentacle up to 10 mm. Mesogleal basal aboral thickening of tentacles visible in preserved specimens (fig. 19C).

Internal anatomy and histology (fig. 19): Marginal sphincter musculature mesogleal (fig. 19D). Longitudinal musculature of tentacles ectodermal (figs. 19E); mesogleal basal aboral thickenings in every outer tentacle (fig. 19F). Actinopharynx up to 35 mm in length, approxiwas established based on only two specimens one of which showed empty ovarian follicles (Riemann-Zürneck, 1973) and the presence of gametogenic tissue on the second and third cycles of mesenteries could be clearly confirmed in our material (see fig. 19I, J) we assume this difference is due to such difficulties.

Material: MNRJ 4227 (2 specimens); locality: REVIZEE Bahia 2, R/V Thalassa, Sta. EO523, sector 1, dredging 29, southwestern Atlantic, Brazil, off the coast of Espirito Santo (ES), 19°51.48′ S 38°32.5′ W, collected on 27 June 2000 (922 m). MNRJ 4358 (2 specimens); locality: REVIZEE Central 1, R/V Thalassa, southwestern Atlantic, Brazil, off the coast of Rio de Janeiro (RJ), 21°56.27′ S 40°09.98′ W, collected on 22 June 2000 (? m). MNRJ 6783 (2 specimens); locality: Projeto Programa Obs, Bordo da Frota Arrendada Obs Doação de Carlos M.L. Silva, CF/V Kimpo Maru, southwestern Atlantic, Brazil, off the coast of Rio Grande do Sul (RS), 33°46.1′ S 52°0.03′ W, collected on 27 July 2002 (526 m).

Material examined: Phelliactis lophohelia: ZMH CZ7542 (1 specimen; holotype); locality: Walther-Herwig Expedition, southwestern Atlantic Ocean, between 22°–38° S, collected between 22 February 1968 and 15 March 1968 (800 m). Phelliactis gigantea: ZMUC ANT-000029 (1 specimen; holotype); locality: Th. Mortensen's Java–South Africa Expedition, St. 80A, tropical east Atlantic, St. Helena, 3 km SE of Longe Range Point, collected on 24 February 1930 by Th. Mortensen, “Dana” (360 m).

External anatomy (fig. 21): Body long and flattened at directive axis in preserved specimens (fig. 21A). Pedal disc curved, flattened at directive axis, 16–110 mm in diameter in preserved specimens (fig. 21A). Column flattened at directive axis, covered by cuticle (fig. 21A) often only in area between tubercles (fig. 21A, B); tubercles not pointed but smooth (fig. 21A, C). Column visibly divisible into scapus and short capitulum in preserved specimens (fig. 21A). Margin of capitulum tentaculate (fig. 21C). Column white in preserved specimens with cuticle olive green (fig. 21A). Column 42–71 mm in diameter and 52–104 mm in length in preserved specimens. Oral disc large, clearly bilobed, wider than column in preserved specimens (fig. 21A); 32–52 mm in diameter in preserved specimens. Tentacles 171–182, short, slender and pointed, displaced to margin of oral disc but contracted within oral disc.

Internal anatomy and histology (fig. 21): Body with wall thickness fairly uniform along column: epidermis and gastrodermis thinner than thick mesoglea (fig. 21C); limit between scapus and capitulum gradual. Marginal sphincter musculature mesogleal, long, narrow, equidistant from epidermis and gastrodermis (fig. 21C); fibers with alveolar arrangement (fig. 21D). Column with “spongy” texture in some areas (fig. 21E). Longitudinal musculature of tentacles ectodermal (fig. 21F); all tentacles with mesogleal basal aboral thickenings (fig. 21G). Actinopharynx up to 30 mm in length, approximately half of column's length; longitudinally sulcated throughout; with thick and highly glandular epidermis (not shown). Specimens with two differentiated siphonoglyphs with thin gastrodermis and epidermis and thick mesoglea (fig. 21H).

Mesenteries mostly hexamerously arranged in five cycles (6+6+12+24+37 = 85 pairs) in most of body length: at actinopharynx-level first cycle perfect, including two pairs of directives, each associated with one siphonoglyph (fig. 21H); two or three additional pairs of mesenteries of second cycle perfect. Remaining pairs of second to fifth cycles imperfect (fig. 21H). Specimens with irregularities in arrangement of mesenteries including 9 missing pairs of fifth cycle (asterisks: fig. 21H); missing pairs of fifth cycle always close to pairs of third cycle. Mesenteries of first to fourth cycles, including directives, with filaments; those of second to fourth cycles fertile (fig. 21H, I). Retractors of first to third cycles strong, diffuse (fig. 21H–J); those of fourth cycle weak (fig. 21I) and those of fifth cycle absent (fig. 21J). Parietobasilar musculature strong in all mesenteries (fig. 21I, J). Species gonochoric: major axis of oocytes 70–189 µm in diameter (fig. 21I); major axis of spermatic cysts 126–549 µm in diameter (fig. 21L) in specimens collected in June. Basilar musculature of mesenteries weak (not shown).

Cnidom (fig. 22): Spirocysts, basitrichs, p-mastigophores B1. See figure 22 and table 10 for size and distribution of cnidae.

Distribution and natural history: Phelliactis pelophila is widely distributed in Brazil, including the Espirito Santos Basin and the Campos Basin in the southeastern region and the Pelotas Basin in the southernmost state of Rio Grande do Sul. All of the specimens collected in Brazil represent a range extension for P. pelophila that had previously been collected only off the coast of Uruguay (Riemann-Zürneck, 1973). Our records extend the bathymetric range of the species to relatively shallower waters (526–922 m) compared to the type material (800–1000 m: Riemann-Zürneck, 1973).

Remarks: The eight (MZUSP 4227, MZUSP 4358) or nine (MZUSP 6783) pairs of perfect mesenteries, the relatively small and flat tubercles on column, the gametogenic tissue present on third and fourth cycles of mesenteries, p-mastigophores B1 in the tentacles as well as similar retractor, parietobasilar and marginal sphincter musculature of our specimens agree perfectly to the description of Phelliactis pelophila by Riemann-Zürneck (1973). Again, the only major difference between the type material of P. pelophila and our specimens is the fertility pattern: gametogenic tissue only on mesenteries of fourth cycle in type material and gametogenic tissue on mesenteries of third and fourth in our specimens (see fig. 21H).