Pyrolycus jaco Frable, Seid, Bronson & Møller, 2023

Frable, Benjamin W., Seid, Charlotte A., Bronson, Allison W. & Møller, Peter Rask, 2023, A new deep-sea eelpout of the genus Pyrolycus (Teleostei: Zoarcidae) associated with a hydrothermal seep on the Pacific margin of Costa Rica, Zootaxa 5230 (1), pp. 79-89 : 81-86

Pyrolycus jaco Frable, Seid, Bronson & Møller , sp. nov.

( Figures 1–4 , Table 1 )

LSIDurn:lsid:zoobank.org:act: 1EF499D0-6042-41A5-8E85-0B35A087CBB2

Pachycara sp. — Levin et al., 2012: Fig. 2d .

Holotype: SIO 20-41 (ex SIO-BIC BI1339 ), 107+ mm SL, Costa Rica, Jacó Scar , 9°7.041′ N 84°50.375′ W, 1795 m depth, 18 Oct 2018, HOV Alvin dive 4972, suction sampler, G. Rouse and A. Hiley.

Paratypes: SIO 20-42 (ex SIO-BIC BI1661 ), 95+ mm SL (in two pieces), Costa Rica, Jacó Scar , 9°7.050′ N 84°50.438′ W, 1768 m depth, 04 Nov 2018, HOV Alvin dive 4989, suction sampler, L. Levin and D. Casagrande ; MZUCR 3319 (ex SIO 20-43 ; ex SIO-BIC BI1662 ), 90+ mm SL, Costa Rica, Jacó Scar , 9°7.071′ N 84°50.445′ W, 1746 m depth, 17 Oct 2018, HOV Alvin dive 4971, “Bushmaster” device (in tubeworm mass), E. Cordes and R. Rutstein ; ZMUC P2397865 (ex SIO 20-44 ; ex SIO-BIC BI1663 ), 72+ mm SL, Costa Rica, Jacó Scar , 9°7.067′ N 84°50.367′ W, 1785 m depth, 04 Nov 2018, HOV Alvin dive 4989, suction sampler, L. Levin and D. Casagrande .

Diagnosis. A species of Pyrolycus differentiated from its congeners with the following combination of characters: five suborbital bones (vs. six) with 5 pores, occipital pores 2, postorbital pores 3, vertebrae 23 + ~57 = ~80, vomerine and palatine teeth present, total gill rakers 2–3+13–15= 16–17, pectoral fin rays 14–15, upper jaw short 33.9–42.4% HL and snout short 21.3–24.3% HL. It is specifically separated from Pyrolycus moelleri in having fewer precaudal vertebrae and total vertebrae, palatine teeth present (vs. absent), three postorbital pores (vs. two) and 14–15 pectoral-fin rays (vs. 13–14). And from P. manusanus by having two occipital pores (1-0-1 vs. one, 0-1- 0), more gill rakers, fewer vomerine teeth, more palatine teeth, fewer pectoral-fin rays, a larger eye diameter, and a narrower gill slit.

Description. Counts and morphometrics are presented in Table 1 . Body and head gelatinous; body elongate and compressed posteriorly. Scales and lateral line absent. Peritoneum dark. Head slightly compressed and ovoid; snout rounded and blunt, not extending beyond upper jaw. Eyes round to slightly ovoid and small, not in dorsal profile of head; interorbital space flat to slightly concave, half snout length; nostrils tubular, ca. 5.6 times in snout length. Gill slit long extending ventrally to or just above pectoral-fin base.

Mouth terminal to slightly oblique, posterior edge of maxilla reaching mid-orbit; lips on upper and lower jaw moderately thick. Oral valve weak. Teeth simple and conical. Premaxilla teeth in 2 rows near symphysis becoming a single row posteriorly; 14 teeth in outer row with 5–6 in inner row; outer teeth longer with very slight recurve, those near symphysis longest and more fang-like. Dentary teeth in 2 rows near symphysis becoming single row posteriorly; 15 teeth in outer row with 5–6 in inner row; outer row teeth longer and slightly recurved. Vomerine teeth slightly recurved, in cluster with 7–8 teeth arranged in wedge; palatine teeth simple, 12–15 teeth in single row. Gill rakers short and triangular. Pseudobranch filaments 5. Pyloric caeca present as two nubs.

Cephalic lateralis pores large and round. Nasal pores 2, anteromedial and posteromedial to nostril tube. Suborbital pores 5, arranged in reversed L-shape. Postorbital pores 3 (1, 3 and 4). Preoperculomandibular pores 8, 4 from dentary, 1 from anguloarticular and 3 from preopercle. Interorbital pore absent. Occipital pores 2 (1-0-1), on either side, smaller than other pores ( Fig. 3 ).

Dorsal fin origin on a vertical just before middle of pectoral fin, associated with vertebra five, first two dorsal pterygiophores between vertebra four and five. Anal fin origin before midbody, below first caudal vertebra, first three pterygiophores inserted anterior to first caudal vertebra haemal spine. Pectoral fin origin near body midline; pectoral fins rounded, reaching vertical through 7th–8th dorsal-fin ray. Pelvic fin short and reduced, just anterior pectoral-fin base. Caudal fin destroyed in all specimens.

Neurocranium long. Parasphenoid wing low, at ventral margin of trigeminal foramen but with anteriodorsal projection to just below mid-level of foramen ( Fig. 2A ). Suborbital bones 5, thin and widely spaced, arranged in reversed L-shape ( Fig. 2B ). Palatopterygoid series weak, ectopterygoid and mesopterygoid overlapping less than half dorsal and anterior surfaces of quadrate. Metapterygoid reduced and weak.

Coloration in life ( Fig. 1A , 4 ). Body light pink to pink lavender, semi-translucent; gut slightly darker than trunk. Top and sides of head somewhat translucent and dark violet, snout pink, anterior of snout and jaw reddish pink. Eyes dark blue-black. Fins light, pale lavender to pinkish, semi-translucent. Faint brownish mottling on body, head and pectoral fins.

Coloration in preservation ( Fig. 1B ). Holotype uniformly tan, body semi-translucent. Fins tan with slight mottling on pectoral fins. Paratypes in 95% ethanol, light tan with very faint mottling body, head and fins (especially SIO 20-42).

Etymology. Named for the type locality and only known habitat, the Jacó Scar site on the Pacific Costa Rica margin, which itself is named in honor of the nearby coastal district of Jacó, Puntarenas, Costa Rica. Name treated as an appositional noun.

Habitat and distribution. Specimens were collected or observed in association with colonies of the tubeworms Lamellibrachia barhami and Escarpia spicata at depths of 1604–1854 m exclusively at Jacó Scar.

Diet. The new species feeds, at least in part, on benthic sessile invertebrates associated with the hydrothermal seep area. Dissection of SIO 20-42, radiographs and CT scans reveal shells of Lepetodrilus sp. McLean, 1988 and other limpets, as well as a snail in the gut of these specimens.

Comparisons. The new species is readily differentiated from congeners in having five suborbital bones (vs. six in the other two species), shorter snout (21.3–24.3 vs. 25.8–29.3% HL) and shorter upper jaw (33.9– 42.4 vs. 37.8–42.3% HL). It is further separated from Pyrolycus moelleri in having fewer precaudal vertebrae (22–23 vs. 28) and total vertebrae (~80 vs. 95–96), palatine teeth present (vs. absent; Fig. 2A ), three postorbital pores (vs. two; Fig. 3 ) and 14–15 pectoral-fin rays (vs. 13–14). It is differentiated from P. manusanus by having two occipital pores (1-0-1 vs. one, 0-1-0; Fig. 3 ), more gill rakers (2–3+13–15= 16–17 vs. 1–2+12–14=13–15), fewer vomerine teeth (7–8 vs. 10–12), more palatine teeth (12–15 vs. 5–6), fewer pectoral-fin rays (14–15 vs. 16–17), larger eye diameter (12.1–14.9 vs. 8.3% HL), and a narrower gill slit (26.9–34.7 vs. 41.7% HL).

The new species is readily separated from the other two thermophilic genera, Thermarces and Pachycara . It is differentiated from all three species of Thermarces by having a weakly-developed palatopterygoid series (vs. well-developed; Fig. 2A ), five suborbital bones and pores (vs. six; Fig. 2B ), pelvic bones and fin-rays present (vs. absent), occipital pores present (vs. absent), and fewer precaudal and total vertebrae (22–23 vs. 29–32; ~80 vs. 92–97, respectively).

Pyrolycus jaco sp. nov. is distinct from members of Pachycara by the absence of scales (except present in P. shcherbachevi Anderson, 1989 ( Møller 2003) from the northern Indian Ocean and P. alepidotum Anderson & Mincarone, 2006 and P. matallanasi Corbella & Møller, 2014 ) and a lateral line and in having fewer total vertebrae (~80 vs. 92–125), 2 occipital pores (vs. 0–1), a low parasphenoid wing (vs. high; Fig. 2A ), and a weak palatopterygoid series (vs. well-developed).

Finally, Pyrolycus jaco sp. nov. can be compared to the genus Dieidolycus Anderson, 1988 in sharing characters such as five suborbital bones, three postorbital pores, and 22–23 precaudal vertebrae, but is readily differentiated by having a low parasphenoid wing (vs. high in Dieidolycus ), 14–15 pectoral-fin rays (vs. 16–17), and two occipital pores (vs. 0).

The COI sequence for the holotype (609 bp; SIO 20-41; GenBank: OP234394 ) was 99.84% identical to that of the tissue sample reported in Levin et al. (2012; GenBank: OP234395 ; voucher not located; tissue catalogued as SIO 22-90 [ex SIO BIC BI1642]). BLAST results revealed that there are no other highly similar (>98%) sequences in GenBank, with the most similar being 95.4% for Lycenchelys tristichodon DeWitt & Hureau, 1980 (GenBank: HQ713043.1, HQ713045.1 and KX676058.1) and 95.2% for Pachycara angeloi Thiel, Knebelsberger, Kihara & Gerdes, 2021 (GenBank: MW888715.1). These results demonstrate that the new species is most closely related to other lycodine genera. However, there are not enough available sequences of lycodine species to evaluate the molecular phylogenetic relationships of this species and much of this group in general.

Figures

FIGURE 1. Holotype of Pyrolycus jaco sp. nov., SIO 20-41, 107+ mm SL, Jacó Scar, Costa Rica A) freshly collected; B) in preservation, note caudal region removed by collectors; C) superimposition of radiograph over fresh image to estimate vertebral count. Scale bar= 20 mm.

FIGURE 2. CT-image of the lateral left side of the head of SIO 20-41, holotype, Pyrolycus jaco sp. nov., 107+ mm SL, with A) parashpeonid and palatopterygoid series and B) orbital series highlighted. Scale bar = 5 mm.

FIGURE 3. Pore configuration on the dorsal surface of the head in Pyrolycus jaco sp. nov., holotype, SIO 20-41, 107+ mm SL. PO: postorbital pores; OCC: occipital pores. Scale bar = 2 mm.

FIGURE 4. Live images of Pyrolycus jaco sp. nov., not collected, living among Lamellibrachia barhami and Escarpia spicata colonies. Photo credit: ROV SuBastian/Schmidt Ocean Institute.