Porogadus promelas Gilbert, 1892

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 : 71-74

Porogadus promelas Gilbert, 1892

Figs. 36–37 , 47 , 50 , Tab. 1–7

Porogadus promelas Gilbert, 1892: 546 ; Hanke et al. 2015: 74, fig. 6.

Porogadus breviceps Garman, 1899: 155 .

Porogadus catena (not Goode & Bean, 1885): Carter & Sulak 1984: 374 (part).

Porogadus (Moebia) promelas: Nolf 1980: 91 , pl. 11, fig. 11 (otolith).

Porogadus (Moebia) sp.: Schwarzhans 1981: 94, fig. 92 (otolith).

Material examined (14 specimens): Specimens labeled as P. promelas : Lectotype and paralectotype USNM 48265 , 237 and 125 mm SL, 27°39’N 111°42’W, 1838 m, Albatross Expedition 1883-1900, Sta. D 3010, large beam trawl, 20 March 1889 ; paralectotype USNM 125002, 218 mm SL, 27°39’N 111°42’W, 1838 m, Albatross Expedition 1883-1900, Sta. D 3010, large beam trawl, 20 March 1889 ; ZMUC P2397228 , R / V Ak. Kurtshatov 239A, 205 mm SL, 23°21’S 71°00’W, 3960 m ; CAS SU 7, 197 mm SL, Baja California Sur, 1838 m ; RBCM 010-00342 - 001 , 280 mm SL, 51°25’N 130°40-41’W, 1967 m ; ZMUC P2397212-213 , 154 and 243 mm SL, Galathea 2 expedition, Sta. 726, 32 m wide herring otter trawl, Gulf of Panama, 05°49’N 78°52’W, 3270–3670 m, 13 May 1952 ; ZMUC P2397214-218 (5 specimens), 110+ to 160 mm SL, Galathea 2 expedition, Sta. 716, 32 m wide herring otter trawl, off Acapulco, Panama, 09°23’N 89°32’W, 3570 m, 6 May 1952 . Specimens labeled as P. breviceps : Lectotype MCZ 28654, 245 mm SL, Gulf of California , 26°48’N 110°45’W, 1571 m , R / V Albatross , small beam trawl, 22 April 1891 .

Diagnosis. Precaudal vertebrae 16–17; long gill rakers on first gill arch 15–18; pectoral-fin rays 17–18; HL: HD 1.50–1.72; few and mostly weak head spines, present on ethmoidal, interorbital, supraorbital, sphenotic, outer posttemporal; absent on lacrimal, prefrontal, 5th infraorbital, supratemporal, inner posttemporal, inner and outer preopercular rim; opercular spine weak, flat; opercular flap small; lower lateral line pores until beginning of anal fin 16–18; vomer with narrow dentition patch with 2–4 rows of teeth; palatines with moderately broad dentition patch with 4–9 rows of teeth; otolith with single colliculum; OL:OH = 1.25–1.5; OL:TCL = 2.0–2.1.

Description (holotype values refer to P. promelas ). Meristics: precaudal vertebrae 16–17, 0–1 last vertebrae without ribs; pectoral-fin rays 18 (17–18); D/V = 5–6; D/A = 24–29; V/A = 18–19; long gill rakers on first gill arch 18 (15–18). Gill rakers in paralectotype (USNM 125002) on lower first gill arch with five plate like rakers, followed by a series of 15 long rakers. The lower 10 of those intercept by broad plate shaped rakers, placed between the long rakers. Upper gill raker with a series of four semi long rakers and five plate like rakers intercepted.

Morphometrics: in % of SL: HL 15.1 (14.4–16.6); maximal HD 9.9 (8.8–11.5); HD through center of eye 6.1–7.8; bony interorbital width 2.4–3.5; snout length 4.8 (4.5–5.8); upper jaw length 9.0 (8.7–10.5); predorsal 16.8 (15.6–19.1); preanal 31.7 (29.0–32.0); prepelvic 11.7–13.2; prepectoral 15.1–16.9; pectoral length 8.3–9.8. Relations: HL:HD = 1.53 (1.50–1.72); HL to snout length 3.18 (2.81–3.18); preanal to predorsal 1.88 (1.67–2.05); predorsal to prepectoral 0.96–1.13.

Slender fish with long tapering tail and relatively short head and snout. Maximal size of fishes investigated 280 mm SL (RBCM 010-00342-001). Head relatively short and compressed, with mostly flat dorsal profile, and mostly weak spines as follows: ethmoidal (1 small), interorbital (1–2 weak), supraorbital (1 weak), sphenotic (2–3 weak), outer posttemporal (1–2 weak); no spines on lacrimal, prefrontal, 5th infraorbital, supratemporal, inner posttemporal, inner and outer preopercular rim (rare up to 2 denticles on inner preopercular rim). Opercle with weak, flat spine. Eye moderately 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; extensive cavernous system on head top in front and lateral of occiput. Head squamation only discernable on opercle, cheeks and occiput; those on cheeks larger than those on opercle or occiput. Opercle with two moderately sized neuromast behind preopercular edge; opercular flap small. Lateral line rows rarely well visible and therefore number of pores countable only in rare instances. Lower lateral line row with 16–18 pores until beginning of anal.

Dentition. All teeth tiny and cone-shaped. Vomer with shout dentition patches with 2–4 rows of tiny teeth anteriorly and 1–2 rows posteriorly; palatines with a broad dentition patch with 4–9 rows of teeth in the middle part. Premaxilla tooth patches broad and not fused anteriorly; ca. 10 rows of teeth in middle part. Dentary tooth patches fused anteriorly; ca. 6 rows in the middle part. Basibranchial tooth patches consisting of long, narrow median patch sometimes accompanied by small single lateral patch and in case of one syntype of P. breviceps ( MCZ 28654) with pair of lateral patches .

Otolith morphology (n = 3). Size 2.6 mm in length; OL:OH = 1.25–1.51; OH:OT = 1.75–2.5. Moderately thick to thick, small, moderately compressed otolith. Dorsal rim with mostly prominent predorsal lobe or rounded predorsal angle; ventral rim shallower than dorsal rim. All rims smooth. Inner face flat, with short, centrally positioned sulcus; OL:TCL = 2.06–2.12. Sulcus with undivided, uniform, sometimes deepened, oval, narrow colliculum. Dorsal field with broad, sometimes distinct depression; ventral field with faint ventral furrow close to ventral rim of otolith. Outer face smooth, with prominent umbo in front of center.

Coloration. Live coloration not known. Color of preserved specimens light to medium brown; only opercle distinctly darker.

Discussion. Porogadus promelas was considered a synonym of P. catena from the West-Atlantic by Carter & Sulak (1984), but we found a number of mostly subtle differences, with the otolith being the most obvious one, to distinguish both species (see above).

Distribution. Porogadus promelas is widely distributed along the deep continental slopes of the central East- Pacific from about 51°N to 23°S and has been caught between 1500 and nearly 4000 m.

Genus Tenuicephalus n. gen.

Type species: Porogadus silus Carter & Sulak, 1984

Diagnosis. A genus of the subfamily Neobythitinae characterized by the following combination of characters: Body long and slender; depth at anus more than 10 times in standard length, prominent mucous cavities and large pores along the infraorbital and mandibular-preopercular canal systems; spines on head very few and weak or absent; upper jaw ends well behind eye; head very weakly ossified and head bones very thin and flexible; 1 narrow median basibranchial tooth patch (except sometimes missing in T. silus ), no lateral basibranchial tooth patches; lateral line not discernable; developed gill rakers 14 to 21; pectoral-fin rays 16 to 19; precaudal vertebrae 14 to 17; ratio HL: HD 1.35 to 1.6; vomer naked or with few singular teeth or with 1 to 2, rarely 3 rows small villiform teeth anteriorly; palatine narrow with 2 to 3 rows small villiform teeth. Body color uniformly black or purple-black, but may fade to medium brown after long term preservation.

Similarity. Tenuicephalus is most remarkable for its weakly ossified head bones and the short and stubby head and snout. It differs from Porogadus , where its species have been placed in the past, additionally in the absence of discernable lateral line systems on the trunk, no or very weak and few head spines and a much reduced dentition on vomer, palatines and basibranchial tooth patches. All these characters are considered derived in the group containing the genera Porogadus , Alcockia , Bathyonus and Penopus and might be related to a live above the ground and feeding on very small crustaceans, as suggested by Carter (1984). These characters are probably autapomorphic in the context of this group of genera and we therefore assume that Tenuicephalus may represent a clade as sistergroup to the other four genera of the lineage.

Ethymology. From tenuis (Latin = thin, weak) and cephalus (Latin = head), referring to the delicate and weak nature of the head ossification which results in often damaged specimens recovered from deep-water trawls.

Species. We consider four species in Tenuicephalus two of which are replaced from a former position in Porogadus and two are newly described here: Tenuicephalus melampeplus ( Alcock, 1896) from the western Indian Ocean and the Solomon Sea, Tenuicephalus multitrabs n. sp. from the Indian Ocean and the West-Pacific, Tenuicephalus silus ( Carter & Sulak, 1984) from the Caribbean, and Tenuicephalus squamilabrus n. sp. known disjunctive from the southwestern Indian Ocean and the West-Pacific.

Remarks. Fishes of the genus Tenuicephalus are exceptionally fragile. We have found only very few specimens in the collections that are well enough preserved to allow for an assessment of characters other than meristics, basic morphometrics, and otoliths (when not eroded by formalin). Particularly squamation, head pore systems and head morphometrics are only rarely identifiable or measurable. Hence the following key, diagnoses and descriptions rely on few specimens for those characters.

Key to the species of Tenuicephalus

1 Long gill rakers 14–16 (up to 18 in T. silus ); HL in % SL 16.4–17.6; no head spines................................ 2

- Long gill rakers 17–21; HL in % SL 14.4–16.2; weak ethmoidal and interorbital spines.............................. 3

2 Loin vertebrae 3; opercular spine sharp; OL:OH <1.0.................................. Tenuicephalus melampeplus

- Loin vertebrae 8–10; opercular spine flat; otolith not known.................................... Tenuicephalus silus

3 Head squamation on occiput, cheeks, opercle and maxilla (but rarely preserved); maximal HD:HD through eye 1.75–1.90; OL in % HL 5.0–6.5; OL:TCL 1.94–2.30.......................................... Tenuicephalus squamilabrus n. sp. - Head naked except scales on cheeks; maximal HD:HD through eye 1.35–1.70; OL in % HL 11.5–14.5; OL:TCL 2.46–2.92............................................................................ Tenuicephalus multitrabs n. sp.

Figures

FIGURE 36. Porogadus promelas Gilbert, 1892; 36A,C,E, CAS SU 7, 197 mm SL, Baja California Sur, 1838 m; 36B,D, MCZ 28654, lectotype of Porogadus breviceps, 245 mm SL, 26°48’N, 110°45W, 1571 m; 36E, USNM 48265, paralectotype, 125 mm SL, 27°39’N, 111°42’W, 1838 m.

FIGURE 37. Porogadus promelas Gilbert, 1892; 37A, USNM 48265, lectotype, 237 mm SL, 27°39’N, 111°42’W, 1838 m, head drawing; 37B, RBCM 010-00342-001, 280 mm SL, 51°25’N, 130°40-41’W, 1967 m, head drawing; 37C–D, MCZ 28654, lectotype of Porogadus breviceps, 245 mm SL, 26°48’N, 110°45W, 1571 m, head drawing; 37E–F, USNM 125002, paralectotype, 218 mm SL, 27°39’N, 111°42’W, 1838 m, otolith (E inner face, F ventral view); 37G, PZMUC P2397228, 205 mm SL, 23°21’S, 71°00’W, 3960 m, otolith (inner face); 37H–I, MCZ 28654, lectotype of Porogadus breviceps, 245 mm SL, 26°48’N, 110°45W, 1571 m, otolith (H inner face, I ventral view).

FIGURE 47. Geographic distribution of the species of the Porogadus catena group.

FIGURE 50. Depth versus distance from shelf plots for specimens of the Porogadus trichiurus group (upper panel) and the Porogadus catena group (lower panel).