The Systematics of the Ophidiid Genus Spectrunculus (Teleostei, Ophidiiformes) Revisited with Description of a New Species and Resurrection of S. radcliffei

After a preceding revision based on 87 specimens, the systematics of the abyssal giant cuskeel genus Spectrunculus Jordan and Thompson, 1914 has been revisited, based on the examination of 34 additional specimens and new otolith shape data of the holotype of S. grandis. From the latter, a clear distinction in otolith ostium width could be found in specimens from the Atlantic, Southern Indian Ocean, and Southwest Pacific, which were formerly identified as S. grandis. Consequently, the new species, S. stenostio, is described, which has a narrower ostium when related to its length or to sulcus length and differs also in the combination of three body shape characters, three meristic characters, and maximum size from the three other congeners, S. crassus (Atlantic, East Pacific), S. grandis (Pacific), and the previously synonymized S. radcliffei (Pacific, Southern Indian Ocean, Southeast Atlantic). The latter species is here resurrected based on a rather short pre-anal length and additional morphometric as well as meristic and maximum size differences. An identification key for the four species of Spectrunculus is provided.

T HE ophidiid deep-sea fish genus Spectrunculus Jordan and Thompson, 1914 belongs to the subfamily Neobythitinae, a rather diverse group of cuskeels found in a large variety of habitats mostly close to the bottom, from the shelf to more than 4000 meters depth (Cohen and Nielsen, 1978;Nielsen et al., 1999).This group is still the subject of intense taxonomic studies with new taxa being described and systematic information updated (e.g., Nielsen et al., 2015;Ohashi, 2018;Uiblein and Nielsen, 2018, 2019, 2021, 2023;Schwarzhans and Møller, 2021;Nielsen and Uiblein, 2022;Schwarzhans et al., 2022).
The giant cuskeel genus Spectrunculus-with a maximum size of 130 cm SL (ca.140 cm TL)-is among the largest deep-sea fishes known.Uiblein et al. (2008) revised the genus based on 87 specimens from the Atlantic and Pacific Oceans, resurrecting the species S. crassus (Vaillant, 1888) that had been synonymized by Nielsen and Hureau (1980).
Since our last revision, comparative data of 34 additional specimens of Spectrunculus have been collected and analyzed together with earlier published as well as previously not considered or newly generated data.This allows for a more refined and detailed distinction among different forms occurring in various areas of the three major oceans.For instance, new otolith shape data of the holotype of Spectrunculus grandis (type locality Japan, NW Pacific) became available suggesting a clear distinction from specimens of the Atlantic, previously considered conspecific in our former revision (Uiblein et al., 2008).Furthermore, detailed morphological studies of specimens of Spectrunculus from the South Atlantic, Southern Indian Ocean, and Pacific (including three recently obtained specimens from Japan) indicated the need to reconsider the formerly synonymized S. radcliffei as a valid species.
Thus, in the present study, we describe S. stenostio, new species, and resurrect S. radcliffei, considering also intraspecific regional and sex-or size-related morphological and color variation in the now four valid species.In addition to diagnostic, descriptive, and distribution information for each species, an identification key is provided.

MATERIALS AND METHODS
Morphometric, meristic, and color data of 121 specimens of Spectrunculus available from Uiblein et al. (2008) or collected during the present study were compiled and analyzed following the methods described by Cohen and Nielsen (1978), Nielsen et al. (1999), and Uiblein et al. (2008).For the descriptions, the following additional morphometric characters that had not been considered previously were collected from a few selected specimens: pectoral-fin width, i.e., the distance between dorsal and ventral pectoral-fin origins; pectoral-fin depth, i.e., the distance between dorsal pectoral-fin and dorsal-fin origins; head depth through eye; and tail length, i.e., the distance between anal-fin origin and posterior end of the vertebrae column.
In addition to radiographs used for obtaining unpaired fin-ray and vertebrae counts, CT scans were used of a few selected, recently collected specimens as well as for obtaining otolith measurements of the holotype of S. grandis.Because otoliths are rather difficult to extract, requiring considerable experience, and may deteriorate with longterm preservation, the identification key is primarily based on non-otholith characters.
One large specimen of Spectrunculus (127 cm SL; CAS-ICH 25724), of which only the right otolith and the posteriormost part of the tail had been retained, had been studied in detail by Hubbs and Follett (1978) when still intact and hence the published meristic and morphometric data were used, while the otolith could be investigated by us.For another large specimen (128 cm SL; CAS-ICH 90121), a hand-written sheet with unpublished morphometric and meristic data from D. J. Long, taken shortly after collection of the specimen, was used.
To consider allometric change, the morphometric data including otolith shape and measurements were separated into two size groups: larger-sized fish ($ 200 cm SL; i.e., subadults or adults) and small-sized fish (,200 cm SL;i.e.,juveniles).
Following Uiblein et al. (2008), four categories of body and head color patterns were identified: pale-body and head white-creamy, gray-whitish, or nearly white, only unpaired fins sometimes brown or dark brown; dark-body, head, and fins brown to dark brown; light brown-intermediate between the two former categories; speckled-body more or less covered by dark irregular spots of varying size on pale background.In the interpretation of color differences, we tried to consider the possible effects of fixation and preservation on color loss ("bleaching").
Morphometric data were rounded to two decimal places in numbers , 4, to one decimal place in numbers , 10, and to whole numbers in higher values except for one decimal place in averages provided in tables.Institutional abbreviations follow Sabaj (2020).Other abbreviations are: HT ¼ Jordan andThompson, 1914 Giant Cuskeel Spectrunculus Jordan andThompson, 1914: 301 (type species by monotypy S. radcliffei Jordan and Thompson, 1914).Parabassogigas Nybelin, 1957: 298 (type , 1996).Considering their large size and relatively common occurrence in distinct areas, species of Spectrunculus may play an important ecological role in deep-sea ecosystems (Uiblein et al., 2008).

Spectrunculus
No reported commercial value.
Origin of dorsal fin above vertebra 9-11, well in front of distal tip of pectoral fin.Pelvic fins with two rays each reaching about 1/3 from its base to anal-fin origin.Pectoral fins on lower half of body, rather short, 10-14 times in SL, and moderately wide at fin base, the width 19-21 times in SL.
Coloration.-Freshly or recently caught specimens with pale creamy body and head, unpaired fins dark brown along distal margins or more entirely, as observed in the 19 type specimens collected by the MAR-ECO cruise, North Atlantic, in 2004.One of those specimens showed in addition several large brown rings on body.Of four specimens collected in the Southern Indian Ocean, the two smaller ones (706-754 mm SL) were dark brown and the two larger ones (962-1001 mm SL) light brown.In three of those specimens, the unpaired fins were dark brown.
Etymology.-Thenew species name is composed of the Greek word for narrow "steno ´s" and the otolith structure "ostium."The ablative of the combined term is "stenostio," meaning "with a narrow ostium." Distribution.-Thisspecies is distributed in the North Atlantic and Southern Indian Ocean to the Southwest Pacific (1694 to 3050 m depth).There are no records from the South Atlantic.
Remarks.-Among the studied specimens that could be sexed were 9 males and 15 females.No sexual dimorphism could be found in any meristic and morphometric characters including otolith characters.A clear negative allometry in otolith length, but not in ostium and sulcus shape, was detected (Fig. 4).Apart from a slight decrease in relative orbit length with size (Fig. 4), no other allometric changes in body shape were encountered in Spectrunculus stenostio.A slight shift towards a lower number of total vertebrae was found in the Indo-Pacific population, while dorsal-and anal-fin ray number do not follow this trend (Table 2).Small-sized specimens (, 200 mm SL) not known; the smallest specimen studied is 248 mm SL.
Otolith (Fig. 3) oval to elongate (length to height ratio 1.34-2.10),with pointed posterior tip.Anterior tip rounded.Sulcus moderately long, 43-72% of otolith length, with separate colliculi and located at the center of inner face.Ostium vertically enlarged, its width 22-30% of sulcus length and 31-40% of ostium length in fish of 187 mm SL and larger; ostium width 59% of ostium length in the 110 mm juvenile.
Coloration.-Fresh or recently caught fish mostly entirely dark brown.Among the 42 specimens collected during the MAR-ECO expedition in the North Atlantic in 2004, 37 showed uniformly dark-brown colored body, head, and fins; one larger specimen (445 mm SL) had a speckled color pattern with dark dots or blotches on pale background on head, body, and fins; four of the five smallest specimens (187-253 mm SL) had light brown body and head color with ventral parts of head and belly pale bluish gray.Longtime preserved specimens including HT are entirely light brown.
Distribution.-Thisspecies is distributed in the Atlantic and East Pacific Ocean (1580 to 4255 m depth).
Remarks.-Among the specimens that could be sexed were ten males and 27 females.No sexual dimorphism could be found in any of the meristic and morphometric characters including otoliths (see also Uiblein et al., 2008).Slight positive allometry in jaw length and negative allometry in orbit length was found (Fig. 4).Orbit in head length in the East Pacific population is slightly shorter than in the Atlantic.Otolith length showed negative allometry, while ostium and sulcus shape did not when the entire size range is considered (Fig. 4).However, the smallest specimen showed a slightly wider and shorter ostium whichwhen combined-indicate an early life-history shift in otolith form (i.e., from small-sized juveniles to larger-sized subadults and adults).No regional variation in meristic characters could be detected.
Otolith (Fig. 3C-E) oval to slightly elongated (length to height ratio 1.20-1.67),posteriorly flattened or with only a Coloration.-Twospecimens collected in the Southwest Pacific in 2000 and 2003 (510-1060 mm SL) both showed light brown body and head color when fresh (the smaller specimen slightly paler and pale grayish from below eye to belly) and were found to be pale after preservation, the unpaired fins still being slightly darker.A large Northeast Pacific specimen (1270 mm SL) had pinkish orange color when fresh (Hubbs and Follett, 1978).The largest specimen studied from the same area collected drifting at the surface in 1996 was still entirely dark brown when studied in 2019.
-Otolith length appears to follow the negative allometric trend as in the other three species of Spectrunculus, and the two largest S. grandis have particularly short pelvic fins (Fig. 4).However, too few specimens were available for study to allow us to investigate intraspecific variation (sex-, size-, or population-related) more closely.Small-sized specimens (, 200 mm SL) not known; the smallest specimen studied is 200 mm SL.
Larger-sized Spectrunculus radcliffei, areas separated, with small-sized HT.   length show negative allometry when the entire size range (i.e., small-sized juveniles to largest-sized adults) is considered (Fig. 4).No such pattern was found for preanal and pelvic-fin length and ostium width.Two of the three smallest specimens (size range 188-190 mm SL) showed a relatively wide ostium compared to all other conspecifics (including the 192 mm SL specimen shown in Figs.3F, 4), possibly indicating early life-history modification in otolith form.Like in Spectrunculus grandis, the largest specimen of S. radcliffei showed a clearly shorter pelvic fin (Fig. 4).Specimens from the South Atlantic show slightly shorter heads, narrower interorbitals, and deeper bodies than in the other areas of occurrence.However, data are insufficient for detailed quantitative population comparisons.
Distinction of each of the four species of Spectrunculus.-(Table 8) Spectrunculus stenostio differs from the other three species by the clearly narrower ostium and by the mostly higher number of total vertebrae; S. crassus differs from the other three species in the combination of low dorsal-fin, anal-fin, and vertebrae counts, mostly larger eyes and lower maximum size; S. radcliffei differs from the other three species in the combination of a mostly shorter preanal length, shorter pelvic-to anal-fin origin distance, and by higher anal-fin ray counts; S. grandis differs from the other three species in the combination of all nine characters.
Color patterns have no significance in species distinction except for fresh or recently collected specimens of the two North Atlantic species, with body and head color in S. crassus being mostly darker than in S. stenostio (see also Uiblein et al., 2008).

KEY TO THE SPECIES OF SPECTRUNCULUS
The key below is prepared to allow identification among the four species of Spectrunculus without necessary extraction of otoliths (see also Materials and Methods section).Consequently, distinction in otolith shape is indicated in parentheses.

Fig. 2 .
Fig. 2. Distribution map showing the occurrence of studied specimens of the genus Spectrunculus.For areas with multiple occurrences, numbers are added to the respective symbols.Type localities are indicated by filled symbols.

Fig. 4 .
Fig. 4. Relationships between morphological characters in the four species of Spectrunculus.
Remarks.-Four valid species with maximum sizes of 60 to 130 cm SL (¼ ca.65 to 140 cm TL) distributed in various parts of the major oceans (for details see species accounts below).Larger juveniles, subadults, and adults occur at or close to deep bathyal and abyssal bottoms (depth range ca.1000 to at least 4255 m), mostly caught by bottom longlining or trawling or photographed in baited landers; larvae and small juveniles are pelagic (Ambrose species by original designation Sirembo grandis G€ unther, 1877).than snout, 5.5 or more times in HL; long rakers on anterior gill arch 7-10; two median basibranchial tooth patches; pelvic fins placed below preopercle; otolith ostium and sulcus well developed; color of head and body uniformly pale creamy or whitish, light or dark brown (rarely pale with dark speckles or rings); unpaired fins often dark when fresh or recently collected; dark pigmentation may not be retained with longer-term preservation.
ric characters as well as the otolith characters are shown in Tables2, 3, and 6.Body elongate, laterally compressed, tapering towards tail.Pectoral-fin depth in HT 7.2 times in SL, tail length 1.80-1.88times in SL, and preanal length 1.04-1.14times in tail length in HT and two non-types.Head length 4.9-5.9 in SL and 2.22-2.89 in preanal length; head depth through eye 8.57 times in SL.Orbit circular, shorter than snout, 1.98-3.27times in snout length.Anterior

Table 5 .
200 mm SL)specimens of two species of Spectrunculus.

Table 6 .
Spectrunculus grandis, type and areas separated.Distribution.-Thisspecies is distributed in the West to Northeast Pacific (1496 to 3431 m depth).