Porogadus turgidus, Schwarzhans & Møller, 2021

Schwarzhans, Werner W. & Møller, Peter R., 2021, Revision of the ‘ dragon-head’ cusk eels of the genus Porogadus (Teleostei: Ophidiidae), with description of eight new species and one new genus, Zootaxa 5029 (1), pp. 1-96 : 46-49

Porogadus turgidus n. sp.

Figs. 20 , 44 , 49 , Tab. 1–7

Material examined ( 2 specimens): Holotype BMNH 1995.11 .22.6, 295 mm SL, 20°55’N 31°11’W, 4500–4610 m, R. R. S. Discovery Cruise semi-balloon otter trawl, 16 October 1993, collected by N. Merrett; paratype BMNH 1995.11 .22.5, 282 mm SL, 20°55’N 31°11’W, 4500–4610 m, R. R. S. Discovery Cruise semi-balloon otter trawl, 16 October 1993, collected by N. Merrett.

Diagnosis. Precaudal vertebrae 17–18; long gill rakers on first gill arch 11–15; HL:HD 1.82–1.85; all head spines strong, present on ethmoidal, lacrimal, prefrontal, interorbital, supraorbital, sphenotic, 5th infraorbital, supratemporal, inner and outer posttemporal, inner preopercular rim, absent along outer preopercular rim; opercular spine sharp, strong, extruding; additional (3rd) postorbital pore, pores on top of head in front of nape; large opercular flap without ridges; lower lateral line pores until beginning of anal fin 18–21; vomer with broad dentition patch (4–7 rows of teeth); palatines with broad dentition patch (6 rows of teeth); otolith with clearly separated ostial and caudal colliculi; OL:OH = 1.6; OL:TCL = 2.45–2.85.

Description. Meristics: precaudal vertebrae 17 (17–18), 1 (1–2) last vertebrae without ribs; pectoral-fin rays 16 (16–18); D/V = 4 (4–5); D/A = 26 (24–26); V/A = 18 (18). Gill rakers in holotype on lower first gill arch with nine plate-shaped rakers, followed by a series of 11 long rakers. The lower four of those intercept by single plate shaped rakers. Upper gill raker with a series of three plate shaped and three slightly longer rakers intercepted, followed by two plate shaped rakers; total long rakers 11 (11–15).

Morphometrics: in % of SL: HL 16.0 (15.3–16.0); maximal HD 9.0 (8.0–9.0); HD through center of eye 6.5 (5.2–6.5); bony interorbital width 2.6 (2.6–3.0); snout length 5.4 (5.0–5.4); upper jaw length 9.3 (9.2–9.3); predorsal 15.7 (15.7); preanal 30.5 (29.6–30.5); prepelvic 13.8 (13.0–13.8); prepectoral 16.6 (16.1–16.6); pectoral length 9.5 (9.5–9.7). Relations: HL:HD = 1.82 (1.82–1.85); HL to snout length 2.95 (2.95–3.07); preanal to predorsal 1.95 (1.88–1.95); predorsal to prepectoral 0.94 (0.94–0.97).

Slender fish with long tapering tail and long, pointed snout. Maximal size of fishes investigated 295 mm SL. Head long and slender, with flat dorsal profile, with strong spines as follows: ethmoidal (1), lacrimal (2), prefrontal (1), interorbital (3), supraorbital (1), sphenotic (2–3), 5th infraorbital (1), supratemporal (1), inner and outer posttemporal (3–5), inner preopercular rim (3–4), no spines along outer preopercular rim. Opercle with sharp, strong, extruding spine. Eye small located in strongly asymmetric orbit. Maxilla extending far beyond eye, strongly widened posteriorly and with distinct supramaxilla. Infra-/postorbital and mandibular-preopercular pores wide, postorbital with 3 pores, the 3rd uppermost one being small, head top with 3 pores on occiput in front of nape and cavernous system extending between squamation of occiput and sphenotic and supraorbital spines. Head squamation on opercle, cheeks, occiput, frontal, around eyes, and possibly on rear of maxilla (indications of scale-pockets). Opercle with three distinct large neuromasts behind preopercular edge; opercular flap large, without radial ridges. All three lateral line rows reasonably well visible. Upper lateral line row with 8–9 pores; lower lateral line row with 18–21 pores until beginning of anal fin; central lateral line row long, lower and central lateral line rows fading behind beginning of anal fin.

Dentition. All teeth tiny and cone-shaped. Vomer with a broad dentition patch with 4–7 rows of teeth anteriorly; palatines with broad dentition patch with 6 rows of teeth throughout. Premaxilla tooth patches not fused anteriorly; ca. 7 teeth rows anteriorly and 3–4 rows posteriorly. Dentary tooth patches fused anteriorly; ca. 6 teeth rows anteriorly and 2–3 rows posteriorly. Median basibranchial tooth patch short, sometimes anteriorly widened.

Otolith morphology (n = 2). Size up to 4.9 mm in length (holotype); OL:OH = 1.6; OH:OT = 2.2–2.6. Moderately thick and moderately elongate otolith, anteriorly broadly rounded, posteriorly slightly expanded and somewhat tapering. Dorsal rim with marked, broadly rounded predorsal lobe, ventral rim regularly curved. All rims smooth. Inner face slightly convex, smooth, with very short, centrally positioned sulcus; OL:TCL = 2.45–2.85. Sulcus with shallow, clearly separated ostial and caudal colliculi; ostial colliculum nearly twice as long and wide as caudal colliculum; OCL:CCL = 1.85–1.90. Dorsal field with indistinct depression; ventral field smooth, without ventral furrow. Outer face smooth, with mild umbo opposite to ostium on inner face.

Coloration. Live coloration not known. Color of preserved specimens medium brown; belly and frontal part of head top slightly darker than body, opercle distinctly darker.

Discussion. Porogadus turgidus is similar to P. miles and the co-occurring P. caboverdensis and P. mendax . External differences are subtle and depending on good preservation (see also discussion to P. miles ). Porogadus turgidus differs from P. miles and P. mendax in the lesser pores of the lower lateral line until the beginning of the anal fin of 18–21 (vs 22–27). Its predorsal length is the shortest in this group (<16 % of SL vs 17–20 %). From P. caboverdensis it differs in the broader vomer (4–7 rows of teeth vs 1–3, rarely 4). It shares with P. caboverdensis the lack of spines along the outer preopercular rim (vs present in P. mendax and P. miles ). It may further differ from P. mendax in the presence of scales on the rear part of the maxilla (scale-pockets; vs no scales on the maxilla). Another useful character to distinguish these four species is the otolith, when preserved. The otoliths of P. turgidus share with those of P. caboverdensis the compressed shape (OL:OH = 1.05–1.6 vs 1.8–2.05 for P. mendax ). Also, most otoliths of P. miles are more elongate (OL:OH = 1.7–2.0, rarely 1.55–1.65, see above). With the otoliths of P. miles it shares the clearly separated colliculi (vs a single, joined colliculum in P. caboverdensis and P. mendax ). The otoliths of P. turgidus differ from those of P. miles in the very short sulcus as expressed in the ration OL:TCL of 2.45–2.85 (vs 1.7–2.05).

Distribution. Porogadus turgidus is one of three deepwater species of the genus occurring in the Cape Verde Basin of the northeastern Atlantic (the other two being P. caboverdensis and P. mendax ). It has been caught at depths between 4500 to 4610 m.

Etymology. From turgidus (Latin) = inflated, referring to the large otolith size compared to its small sulcus size.

Figures

FIGURE 20. Porogadus turgidus n. sp.; 20A–F, BMNH 1995.11.22.6, holotype, 295 mm SL, 20°55’N, 31°11’W, 4500–4610 m, (A–B photographs, C–D head drawings, E otolith inner face, F otolith ventral view); 20G–H, BMNH 1995.11.22.5, paratype, 282 mm SL, 20°55’N, 31°11’W, 4500–4610 m, otolith (G inner face, H ventral view).

FIGURE 44. Geographic distribution of the species of the Porogadus miles group.

FIGURE 49. Depth versus distance from shelf plots for specimens of the Porogadus miles group (upper panel) and the Porogadus gracilis group (lower panel).