Symplectoscyphus marionensis Millard, 1971: 405, fig. 7. – Blanco, 1980: 200, figs 6-13. – Blanco, 1984: 261, figs 1, 2. – Branch & Williams, 1993: 13, unnumbered fig. – Blanco, 1994a: 154. – Blanco, 1994b: 204.

Material examined: MHNG-INVE-129717; Chile, Región de Magallanes y de Antártica Chilena, Strait of Magellan, Stn. 1, WGS84: -53.82408 -71.06608, 5-10 m, coll. Schories & Holtheuer, 01.02.2018; fertile colony on crab carapace.

Description: Colony composed of numerous erect (though unable to support themselves when out of liquid), simple, monosiphonic, up to 2.5 cm high, stems arising from tubular, irregularly-branched hydrorhiza creeping on surface of a crab carapace; perisarc rather thick, striated obliquely, and straw-colored to transparent. Stems with a number of spiral twists (1 to 4 observed) just above their origin from the stolon, then divided into regular internodes by means of deep, oblique constrictions of the perisarc slanting in alternate directions; perisarc thick, with smooth surface, brownish at nodes and straw-colored to transparent elsewhere. Internodes short, slightly geniculate, swollen proximally, then gradually yet distinctly expanding so as to accommodate laterally a hydrotheca, just below the distal node. Side branches pinnately-arranged along the stem and with similar structure, generally given off singly, every 4 stem hydrothecae, by means of short, swollen apophyses borne immediately below the hydrothecal bases. Not rarely, apophyses arise more irregularly, every 1 to 9 hydrothecae, depending on the development of the colony. Branches are generally alternate along the stem. Apophyses are given off on one side of the hydrothecae, not laterally so as to form a coplanar structure; thus, the resulting colony is three-dimensional, displaying decidedly a frontal and a dorsal side, the majority of branches being shifted on anteriorly, forming a wide angle between the two rows. Occasionally, apophyses are also, here and there, given off posteriorly, but this does not alter maintenance of the pinnate structure of the colony. In addition, couples of branches may be rarely given off from both sides of a hydrotheca, forming pairs flanking that theca. Aberrant origins for the side branches are to be found from within some incompletely-formed stem hydrothecae. Main branches rebranch again, forming up to 5th order branches. In all cases, the lower-order branches are significantly shifted with respect to their preceding counterparts, since the apertures of their hydrothecae are situated in a plane forming an almost right angle with that of the hydrothecae belonging to the immediately higher-order branch: while the stem hydrothecae are shifted on to the anterior side of the colony, those of the 1st order branches face upwards, and so on. First internode of a side branch slightly longer than the subsequent ones, with a couple of proximal twists of the perisarc; ordinary internodes of comparable length to those of the stem. Occasionally, clinging organs are given off from tips of both stem and branches, below the hydrothecae; multilobate, flattened laterally, with thick perisarc, gradually becoming thinner towards tips. Hydrothecae alternate, in two parallel rows, generally forming a right angle, occasionally more or less pronounced; tubular, 36-45% adnate to the corresponding internode, gently curving upwards and outwards; free adaxial and abaxial walls slightly convex, with smooth perisarc, comparatively thinner on the former; a perisarc plug at junction between the adnate adaxial wall and the base, occasionally with large, rounded fenestra immediately below or slightly overlapping the base; aperture distinctly thickened, provided with 3 conspicuous, pointed triangular cusps with rounded tips, one adaxial and two lateroabaxial, separated by deep, rounded embayments; adaxial cusp distinctly produced and comparatively less developed than its lateral counterparts; no internal, submarginal cusps; renovations occasional, occurring generally singly. Gonothecae borne on both stems and side branches, predominant on the latter; arising singly, immediately below the hydrothecal bases, on one side of the theca, to which one of their basal walls is apposed, being thus flattened there; sex not determinable in the present material; elongated-oval, tapering below into an indistinct pedicel, above transversely wrinkled, with 6 to 8 complete annular ridges, not forming a spiral, and gradually fading away proximally; distally a rounded, slightly depressed plateau on the top of which is inserted a short, terminal tube, imperceptibly constricted in middle, occasionally somewhat flared at aperture. Cnidome: small and large, banana-shaped microbasic mastigophores, none seen discharged.

Dimensions: See Table 1.

Remarks: The characteristic, unilateral branching pattern met with in S. marionensis results in colonies whose appearance (Fig. 2) resembles that of S. allmani Hartlaub, 1901, described by Galea et al. (2017). This feature was not particularly emphasized by Millard (1971) in her original account, although it is evident from her fig. 7D. The mode of branching and the shape of its gonotheca (her figs 7C and 7B, respectively) leave little doubt that we are dealing with the same species.

A redescription of S. marionensis, based on material from Staten Island, Argentina, was given by Blanco (1980), who was able to compare her specimens to the holotype.

In her account, the unilateral position of hydrothecae and branches, as well as the thickening of the hydrothecal rim, are clearly emphasized.

The size of the colonies reaches as much as 5 cm (Blanco, 1980) or 6 cm (Millard, 1971) high. Millard (1971) observed terminal stolonization in her material, while clinging organs occur in ours.

A number of additional nominal species of Symplectoscyphus occur along the coasts of South America, namely: S. affinis (Hartlaub, 1901) (Hartlaub, 1905), S. bathyalis Vervoort, 1972 (original account), S. chubuticus El Beshbeeshy, 2011 (original account), S. filiformis (Allman, 1888) (Galea, 2007; Galea & Schories, 2012), S. flexilis (Hartlaub, 1901) (Galea & Schories, 2012; Galea et al., 2014), S. interruptus (Pfeffer, 1889) (Galea & Schories, 2012), S. leloupi El Beshbeeshy, 2011 (original account; Galea et al., 2009), S. magellanicus (Marktanner-Turneretscher, 1890) (Galea, 2007; Galea & Schories, 2012), S. milneanus (d'Orbigny, 1842) (Galea et al., 2009), S. modestus (Hartlaub, 1901) (Hartlaub, 1905), S. paraglacialis El Beshbeeshy, 2011 (original account; Galea & Schories, 2012), S. patagonicus Galea & Schories, 2012 (original account), S. salvadorensis El Beshbeeshy, 2011 (original account), S. semper Galea & Schories, 2014 (Galea et al., 2014), S. singularis El Beshbeeshy, 2011 (original account), S. subarticulatus (Coughtrey, 1875) (Galea et al., 2014), S. unilateralis (Lamouroux, 1824) (Galea et al., 2014), S. valdesicus El Beshbeeshy, 2011 (original account), and S. vervoorti El Beshbeeshy, 2011 (original account).

Symplectoscyphus affinis was regarded as a junior synonym of S. magellanicus by Vervoort (1972). So were S. modestus and S. interruptus by Galea & Schories (2012). These statements, however, require a reexamination of the types to be confirmed.

Among the nominal species listed above, S. marionensis is distinctive through its unilateral arrangement of both hydrothecae and side branches, a condition only encountered in the stems of the otherwise rarely branched S. unilateralis. However, their respective gonothecae are morphologically different, and the trophosome of the latter is comparatively smaller in all proportions.

It should be also noted that side branches of S. marionensis are not given laterally, but from insertion points in front or the rear side of its hydrothecae, just below their bases, and consequently do not lie in one plane with the stem (Fig. 3B). A similar branching pattern, with no true axillar hydrothecae, is also met with in some other congeners, e.g. S. flexilis (fig. 6C in Galea & Schories, 2012; fig. 4E¹ in Galea et al., 2014) and S. paraglacialis (fig. 6L in Galea & Schories, 2012).

Distribution: South-African sub-Antarctic islands – Marion Island [Prince Edwards islands, (Millard, 1971)]. Argentina – Isla de los Estados (Blanco, 1980, 1984, 1994b). Chile – Región de Magallanes y Antártica Chilena [Strait of Magellan (present study)].

Sertularia implexa p.p. Allman, 1888: 54, pl. 26 figs 1, 1a. – Hartlaub, 1901: 90. – Bedot, 1916: 223. – Galea et al., 2017: 282, figs 12B, 13A-D.

non Sertularella implexa. – Galea & Schories, 2012a: 40, pl. 3 fig. 4F-J (= Sertularella recta Galea & Schories, 2017).

Sertularella picta. – Vervoort, 1972: 113, figs 34, 35C [non Sertularella picta (Meyen, 1834) = Sertularella gaudichaudi (Lamouroux, 1824)].

non Sertularella picta. – Vervoort, 1972: 114, fig. 35A, B (= Sertularella fuegonensis El Beshbeeshy, 2011).

Material examined: MHNG-INVE-129724; Chile, Región de Magallanes y de Antártica Chilena, Bahía Parry, Stn. 3, WGS84: -54.64663 -69.38810, 10-20 m, coll. Schories & Holtheuer, 05.02.2018; five sterile colonies, 3.5-5.0 cm high. – MHNG-INVE-129727; Región de Magallanes y de Antártica Chilena, Bahía Parry, Stn. 3, WGS84: -54.64663 -69.38810, 10-20 m, coll. Schories & Holtheuer, 05.02.2018; three sterile stems, 0.9-1.2 cm high. – MHNG-INVE-129721; Región de Magallanes y de Antártica Chilena, Bahía Parry, Stn. 2, WGS84: -54.66090 -69.37640, 20-30 m, coll. Schories & Holtheuer, 03.02.2018; two sterile stems, 1.7 and 2.3 cm high.

Dimensions: See Table 2.

Remarks: The colonies from sample MHNGINVE-129721 are similar to those from sample MHNGINVE-129727 (Fig. 5B) regarding their small size and the length of their internodes, compared to the larger, yet still monosiphonic colonies with longer internodes present in sample MHNG-INVE-129724 (Fig. 5A). Despite these minor differences, all materials in hand show no specific differences with the type of S. implexa that was reexamined, redescribed and illustrated by Galea et al. (2017), and reproduced here in Fig. 5C. A comparison of their measurements is given in Table 2.

Only branches of maximum 2nd order occur in the present material, with two consecutive branches being separated by 1-12 successive hydrothecae, the latter lying in one plane, and having the perisarc of their free adaxial wall smooth; their apertures may be renovated 1-3 times, and there are no internal, submarginal projections of the perisarc.

As noted by these authors, the type material, as well as the present specimens, are sterile. Gonothecae are only known from the material likely incorrectly assigned by Vervoort (1972) to S. picta (Meyen, 1834), and believed to belong, with little doubt, to the present species (Galea et al., 2017).

Distribution: Chile – Región de Magallanes y Antártica Chilena [off Isla Nueva (Vervoort, 1972, as S. picta), Bahía Parry (present study)]. Argentina – Provincia de Santa Cruz [off Deseado (Vervoort, 1972, as S. picta)]; Provincia de Tierra del Fuego, Antártida e Islas del Atlántico Sur [off Isla de los Estados (Vervoort, 1972, as S. picta)]. Between Cabo Virgenes and the Falkland Is. (Allman, 1888).

Type material: MHNG-INVE-129725; Chile, Región de Magallanes y de Antártica Chilena, Bahía Parry, Stn. 3, WGS84: -54.64663 -69.38810, 10-20 m, coll. Schories & Holtheuer, 05.02.2018; profuse colony, epizoic on Bougainvillia muscus (Allman, 1863); gonothecae rare; at least one with intact gonophore.

Diagnosis: Colony stolonal with simple, pedicellate hydrothecae, nematothecae and gonothecae arising from creeping, branching, anastomosing hydrorhiza. Hydrotheca almost tubular, tapering slightly below and merging gradually and imperceptibly with its pedicel; basally a thin diaphragm, distally a filmy, pleated operculum, not delimited basally by crease line. Nematothecae elongate. Gonothecae long, tubular, smooth-walled, borne on pedicels of varied length, distally with pleated operculum. Gonophore a medusa.

Etymology: Named after its geographical area of occurrence, the Strait of Magellan.

Description: Colony stolonal, arising from branching, anastomosing hydrorhiza creeping on stem and branches of a hydroid host. Hydrothecae borne singly on top of pedicels of variable length; pedicels with a varied number (generally 2-4) of twists proximally, smooth or with scattered wrinkles elsewhere, though never below the hydrotheca; the latter almost tubular, gently tapering proximally and merging gradually and imperceptibly into its pedicel; separation marked by thin, though distinct, diaphragm; operculum consisting of the filmy, distal perisarc, forming contiguous triangular pleats (not distinct flaps) that meet centrally to form a pyramidal roof; no crease line between the hydrothecal wall and operculum. Hydranths with 22-24 filiform tentacles. Nematothecae scattered on hydrorhiza, pedicellate, with single, distal, ovoid chamber filled with a cluster of banana-shaped nematocysts; perisarc distinctly thickened on pedicel, comparatively thinner around the battery of nematocysts, leaving a small apical, circular aperture. Gonothecae arising from hydrorhiza, borne on either short, spirally-twisted or long, thin, centrally smooth pedicels; tubular, much longer and wider than the hydrothecae; perisarc smooth, except distally where it forms a pleated operculum around the distal aperture, similar to that of the hydrothecae. The gonophore, rather opaque in this fixed material, is most probably a medusa bud. Cnidome of the hydranth: small microbasic mastigophores; elongated-ovoid, unipolarlycurved haplonemes; long, thin, fusiform, gently curved heteronemes; long, fusiform, comparatively stouter heteronemes.

Dimensions: See Table 3 for measurements of the tropho- and gonosome, and a comparison with its congeners. Cnidome: microbasic mastigophores (7.2-7.4) × (2.0-2.3) µm, haplonemes (11.6-15.7) × (2.6-3.7) µm, small heteronemes ca. 27.9 × 3.8 µm, large heteronemes (39.8-43.0) × (5.6-6.2) µm.

Remarks: The current distinction between Oplorhiza Allman, 1877 and Egmundella Stechow, 1921 mainly relies in the shape of their hydrothecae, supposedly ovoid in the former, and funnel-shaped in the latter (Bouillon et al., 2006). This opinion follows Stechow (1921), who regarded Egmundella as not possessing ovoid hydrothecae, the latter showing an imperceptible transition with the hydrocaulus, marked by the presence of a reduced diaphragm. No modern redescription of O. parvula Allman, 1877, the type species of Oplorhiza, is available to date, in order to check this statement, given that illustrations of many hydroid species by Allman proved partly inaccurate (e.g. Billard, 1910).

However, hydrothecae of O. parvula were originally described as “tubular” and “provided with a floor” (Allman, 1877), thus not essentially differing from those of Egmundella. Their supposedly ovoid shape is, in our opinion, not a reliable character supporting a generic separation. However, since hydroids belonging to these genera are not yet related to existing medusae, it is likely useless to consider assigning them a definitive taxonomic status. As most records of hydroids with Campanulinalike hydrothecae and stolonal nematothecae were assigned to Egmundella, this genus is retained to accommodate the hydroid described herein.

Ten nominal species have been assigned so far to Egmundella, two others to Oplorzhiza, and one to Cyclocanna Bigelow, 1918 (Table 3). Although the trophosomes of most appear morphologically uniform, differences in the condition of the stem, the size of the hydrothecae and the shape and position of the nematothecae, could be noted. Gonothecae have been rarely observed in a few species but, when known, they provide reliable characters for a specific separation. In one instance, it has been demonstrated that Cyclocanna welshi Bigelow, 1918 is the medusa stage of the hydroid Egmundella producta (G.O. Sars, 1874), providing a new nomenclatural combination for this animal, as Cyclocanna producta (G.O. Sars, 1874) (Schuchert et al., 2017).

In Egmundella gracilis Stechow, 1921, type species of the genus, the hydrothecal wall does not form a crease line at junction with the operculum [“Das Operculum bildet mit der Thekenwand keinen besonders scharfen Rand” (Stechow, 1921)], and this statement is also stressed in the diagnosis of the genus. Although not expressly indicated, but obvious from Stechow's (1923) fig. Q, the operculum results from a modification of the distal hydrothecal wall, the latter being filmy and pleated there, so as to form a pyramidal roof. In addition, the nematothecae were described as short pedicellate, spherical, monothalamic and immovable [“kurzgestielte, kugelige, einkammerige, unbewegliche Nematophoren mit dicker Peridermwand und einem dicken Bündel sehr großer, langer Nesselkapseln” (Stechow, 1921)].

Although the nematothecae of O. parvula are reportedly said to be pedicellate [“in the form of tubular receptacles with an orifice in the summit” (Allman, 1877: 14)], it is not clear whether its hydrothecae possess a pleated operculum. Indeed, the latter is said “cut into thin collapsible segments” (Allman, 1877: 14), and is depicted as such [Allman's (1877) pl. 7 fig. 2].

Available descriptions of a few nominal species, assigned to either Egmundella or Oplorhiza, suggest that they may possess hydrothecal opercula composed of multiple, distinct flaps, with or without a basal crease line. It is not clear whether this is a normal condition, or these flaps result from the tearing of the filmy, distal, thecal perisarc. For example, the operculum of Egmundella grimaldii Leloup, 1940 is reportedly said to be composed of many pointed, deciduous flaps [“Opercule formé de nombreuses dents pointues, caduques, prolongeant directement l'hydrothèque” (Leloup, 1940: 7)], while that of Egmundella modesta Millard & Bouillon, 1975 possesses “triangular segments clearly demarcated from thecal wall” (Millard & Bouillon, 1975: 5); in a previous description of their species, Millard & Bouillon (1973: 43, as ? Lovenella sp.) report the following: “Margin indented to take the opercular segments which are sharply demarcated from it”. The operculum of Oplorhiza diaphragmata Naumov, 1960 consists of “10-14 narrow triangular plates sometimes folded into a many-sided pyramid over the hydrotheca mouth. No sharp boundary between hydrotheca mouth and operculum” (Naumov, 1969: 337). Reexamination of fresh specimens of these species is therefore necessary to document the exact condition of their hydrothecal opercula.

Besides E. magellanica sp. nov., two other congeners occur in the eastern Pacific, namely E. gracilis and Egmundella polynema Fraser, 1948. The former, originally found in the Vancouver area (Stechow, 1921), was subsequently recorded from southern Chile (Galea, 2007). It is a species with comparatively smaller hydrothecae (Table 3), characterized by the occurrence of the nematothecae not only on the hydrorhiza, but also in small groups a short distance below the thecal bases. The presence of dense clusters of nematothecae on the hydrothecal pedicels of E. polynema, as well as its longitudinally striated gonothecae, make it distinct from the new species described herein.

Two hydroids have been described from the western Pacific, viz. O. diaphragmata and Egmundella humilis Fraser, 1936. The former apparently displays a hydrothecal operculum with a different structure (see above), and its putative gonothecae are long and conical (Naumov, 1969). The latter is a comparatively smaller species than E. magellanica sp. nov. (see Table 3), and its gonothecae are sessile and provided with wrinkled walls (Hirohito, 1995).

Although C. producta occurs on both sides of the North Atlantic [notably its medusa, see Schuchert (2016)], five other hydroids were recorded exclusively from the western Atlantic: Egmundella grimaldii Leloup, 1940, Egmundella fasciculata Fraser, 1940, and Egmundella grandis Fraser, 1941 occur in cold to temperate areas, while O. parvula and Egmundella superba Stechow, 1921 are tropical (see original accounts). The morphology and taxonomic position of C. producta were discussed by Schuchert (2016) and Schuchert et al. (2017), respectively. Egmundella grimaldii and E. superba have larger hydrothecae than E. magellanica sp. nov. (see Table 3), E. fasciculata builds polysiphonic colonies (Fraser, 1940), E. grandis has nematothecae on both the stolon and hydrothecal pedicels (Fraser, 1941), and O. parvula has twisted pedicels immediately below the hydrothecal bases (Allman, 1877), a condition never met with neither in the new species, nor in some of its congeners [e.g. E. modesta, see Millard & Bouillon (1975)].

Finally, three additional species occur in the Indian Ocean, viz. E. modesta, Egmundella valdiviae Stechow, 1925, and Egmundella sibogae Billard, 1940. As noted above, the closing apparatus of E. modesta may be different from that met with in E. magellanica sp. nov., its hydrothecae are comparatively shorter (see Table 3), and its nematothecae are spherical and sessile (Millard & Bouillon, 1975). Although similar in shape, the gonothecae of E. sibogae are of smaller proportions (see Table 3), and this species is kept separate mainly on biogeographical grounds. Similarly, based on its geographical origin, the new species is considered as distinct from E. valdiviae occurring off West Sumatra.

Linking hydroids and medusae under a unified classification and nomenclature can be challenging. However, even though the life cycle of the present hydroid remains to be studied, it has been decided to create a new species for it, mainly because its morphology is different from that of its two other congeners from the eastern Pacific, E. gracilis and E. polynema. In addition, based on biogeographical grounds, it is assumed that the tropical O. parvula, E. superba, E. modesta, E. valdiviae, and E. sibogae, the northwestern Atlantic E. grimaldii, E. fasciculata and E. grandis, as well as the northwestern Pacific O. diaphragmata and E. humilis could reasonably be excluded from the comparison, besides a series of morphological differences displayed by some of them (Table 3). Moreover, Patagonian medusae are poorly known, and the dispersive stage of E. magellanica sp. nov. may well be undescribed.

Sampling new material of hydroids and medusae for molecular studies is required to allow sequence comparisons for matching their life cycles (e.g. Schuchert et al., 2017).

Distribution: Chile – Región de Magallanes y Antártica Chilena [Bahía Parry (present study)].