Porogadus guentheri, Jordan & Fowler, 1902

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 : 49-51

Porogadus guentheri Jordan & Fowler, 1902

Figs. 21–22 , 45 , 50 , Tab. 1–7

Porogadus guentheri Jordan & Fowler 1902: 762, fig. 6; Machida 1982: 27; Machida in Masuda et al. 1984: 101, pl. 85J; Machida in Okamura & Kitajima 1984: 261, 375; Nielsen et al. 1999: 86; Shinohara et al. 2005: 414.

Material examined (13 specimens): BSKU 43444, 257 mm SL, 32°21’N 132°27’E to 32°23’N 132°28’E, 1642– 1651 m , R / V Tansei-maru, 3 m beam trawl, collcted by Okamura , 2 Nov. 1986 ; BSKU 47928 (otolith only), 32°26’N 133°50’E to 32°28’N 133°54’E, 1316–1542 m , R / V Tansei-maru, 3 m beam trawl, 2 Sept. 1990 ; BSKU 86818, 251 mm SL, 32°24’N 132°16’E to 32°25’N 132°17E, 1501–1561 m , R / V Tansei-maru, 3 m beam trawl, coll. Endo and Nagatomo, 16 Dec. 1999 ; BSKU 86819 , 86832 (2 specimens), 248–255 mm SL, 1678–1690 m, 32°18’N 132°21’E to 32°17’N 132°20’E , R / V Tansei-maru, 3 m beam trawl, coll. Endo and Nagatomo, 16 Dec. 1999 ; CAS SU 7124 , paratypes, 137–210 mm SL, 34°97’90N, 139°61’46S, Sagami Sea , Japan no depth information, year 1900 (date unknown) ; NSMT P.66377 (2 specimens), 170–199 mm SL, 961 m, 26°14’N 125°16’E ; NSMT 101668 (2 specimens), 110–120 mm SL, 1276–1319 m, 27°59’N 127°34’E ; SIO 53-366 (2 specimens), 226–235 mm SL , R / V Spencer F Baird , sta. 8, dredge, collected by T. J. Walker, Honshu Island , Kii Strait, S of Kobe, 33°21’N 134°54’E, 1298 m, 23 October 1953 .

Diagnosis. Precaudal vertebrae 16–17; long gill rakers on first gill arch 18–21, broad, bladed; HL:HD 1.71– 1.79; most head spines strong: on ethmoidal, prefrontal, interorbital, supraorbital, sphenotic, supratemporal, inner and outer posttemporal, inner preopercular rim, lacrimal with ridge, weak on outer preopercular rim, absent on 5th infraorbital; opercular spine sharp, extruding; maxilla with single row of scales along upper margin in front of supramaxilla; large opercular flap with ridges; lower lateral line pores until beginning of anal fin 16; vomer with narrow dentition patch with few or 1–2 (rarely 3) rows of teeth; palatines with moderately broad dentition patch (3–6 rows of teeth); otolith with single colliculum but indentation at ventral margin and rarely separate colliculi; OL:OH = 1.45–1.64; OL:TCL = 1.87–2.52.

Description (based on non-types). Meristics: precaudal vertebrae 16–17, 1–2 last vertebrae without ribs; pectoral-fin rays 15–17; D/V = 4–5; D/A = 23–27; V/A = 18; long gill rakers on lower gill arch 18–21, broad, bladed. Gill rakers in a typical specimen (BSKU 86819) on lower first gill arch with six short rakers, followed by a series of 21 long rakers. The lower 11 of those intercept by plate shaped rakers. These are smaller than in most species an placed mostly on the inner part of the gill arch. The long rakers are blade shaped, broader than in most other species and armed with spinules. Upper gill arch with two plate shaped rakers, followed by a series of three semi-long rakers and two plate-like rakers intercepted, followed again by two plate shaped rakers.

Morphometrics: in % of SL: HL 13.9–15.0; maximal HD 7.9–8.6; HD through center of eye 5.7–6.6; bony interorbital width 3.4–4.1; snout length 4.7–5.5; upper jaw length 8.2–9.4; predorsal 13.7–14.7; preanal 26.8–29.3; prepelvic 11.2–12.5; prepectoral 14.6–15.9; pectoral length 8.1–9.8. Relations: HL:HD = 1.71–1.79; HL to snout length 2.66–3.04; preanal to predorsal 1.86–2.05; predorsal to prepectoral 0.90–1.00.

Slender fish with long tapering tail and moderately long snout. Maximal size of fishes investigated 257 mm SL. Head moderately long and moderately slender, with slightly convex dorsal profile, with strong spines and ridges as follows: ethmoidal (1), lacrimal (1 ridge), prefrontal (1), interorbital (3), supraorbital (1–2), sphenotic (2–4), supratemporal (2), inner and outer posttemporal (3–4), inner preopercular rim (5–6), outer preopercular rim (2–3 short and weak), no spines on 5th infraorbital. Opercle with sharp, extruding spine. Eye moderately large, located in strongly asymmetric orbit. Maxilla extending far beyond eye, strongly widened posteriorly and with distinct supramaxilla. Infra-/postorbital and mandibular-preopercular pores wide, head top with cavernous system extending between occiput and sphenotic and supraorbital spines and on occiput in front of nape, sometimes opening in up to 7 bilateral symmetrical openings (pores or damaged thin skin cover?). Head squamation on opercle, cheeks, and single row along upper margin of maxilla in front of supramaxilla, absent on occiput, frontal, and around eyes. Opercle with three distinct large neuromasts behind preopercular edge; opercular flap large, with radial ridges. Lateral line rows rarely well visible and therefore number of pores countable only in rare instances. Lower lateral line row with 16 pores until beginning of anal fin in one specimen.

Dentition. All teeth tiny and cone-shaped. Vomer narrow, anteriorly naked or with short dentition patch with 1–2 (rarely 3) rows of teeth anteriorly, naked posteriorly; palatines with a short and narrow dentition patch with 3–6 rows of teeth in middle part. Premaxilla tooth patches not fused anteriorly; ca. 6 teeth rows anteriorly and 2–3 rows posteriorly. Dentary tooth patches not fused anteriorly; ca. 6 teeth rows anteriorly and 2 rows posteriorly. Median basibranchial tooth patch short.

Otolith morphology (n = 5). Size up to 4.1 mm in length; OL:OH = 1.45–1.64; OH:OT = 2.4–2.9. Relatively thin and moderately elongate otoliths, anteriorly broadly rounded, posteriorly slightly expanded, somewhat less rounded than anterior tip. Dorsal rim with broad, rounded pre- to mediodorsal lobe, ventral rim regularly curved.All rims smooth. Inner face nearly flat, smooth, with short, centrally positioned sulcus; OL:TCL = 1.87–2.52. Sulcus with shallow, usually undivided sulcus, but with indentation of ventral margin at junction (collum) between ostium and cauda, rarely with indistinctly separated colliculi; OCL:CCL = 3.5 in the event of distinctive colliculi ( Fig. 22C ). Dorsal field with large indistinct depression; ventral field smooth, without ventral furrow. Outer face smooth, with mild, anteriorly positioned umbo.

Coloration. Live coloration not known. Color of preserved specimens light brown on body; belly darker and head distinctly darker than body, opercle black.

Discussion. Within the Porogadus trichiurus group, P. guentheri is characterized by an unusual short predorsal length (13.7–14.7 vs 14.5–18.2). It shares with P. trichiurus the bladed nature of the long gill rakers but has many intermittent plates (vs none or very few). It further differs from P. trichiurus in the presence of a sharp and free opercular spine (vs flat and weak), lesser teeth on the vomer, which is often partially naked, the lack of scales on the occiput and around the eye (vs present) and the presence of scales on the maxilla (vs absent), and a much more elongate otolith (OL:OH = 1.45–1.64 vs 1.04–1.27). It differs from P. solomonensis additionally to the predorsal length in the number of long gill rakers (18–20 vs 16–17), the head length (HL = 13.6–15.0 vs 15.3–16.2), the feeble dentition on vomer (naked up to 1–2 rows of teeth vs 4 and more rows of teeth), the absence of paired basibranchial tooth patches (vs present), and stronger head spines, particularly along the inner rim of the preopercle. Porogadus guentheri shares the sharp and extruding spine with P. lacrimatus but differs additionally to the predorsal length in the ratio HL:HD (1.71–1.79 vs 1.52–1.59), and the bladed gill rakers (vs not bladed). Porogadus guentheri is remarkable for a rather large variability in its otolith morphology, which is greater than in other species of the genus, particularly in respect to the degree of separation (or fusion) of ostium and cauda and the range in relative sulcus length (OL:TCL = 1.87–2.52).

Distribution. Porogadus guentheri appears to be endemic to the southern shores of Japan from the Sagami Bay southwards and along the back arc of the Ryukyu Island Chain at moderate depth (900–1700 m) and not venturing away from the shelf break for more than 100 km. Prokofiev (2005) described a single specimen from the Emperor Seamount as Porogadus sp. cf. guentheri and noted that it differed (among others) in the lower number of long gill rakers on the first arch (16 vs 19 in the holotype of P. guentheri ). We have not studied this specimen, but judging from the range observed in Japanese specimens in respect to gill raker counts we would indeed assume, that the specimen from the Emperor Seamount might represent a different species.

Figures

FIGURE 21. Porogadus guentheri Jordan & Fowler, 1902; 21A–B, BSKU 86819, 248 mm SL, 32°18’N, 132°21’E, 1678– 1690 m; 21C, NSMT P.101668, 110 mm SL, 27°59’N, 127°34’E, 1276–1319 m.

FIGURE 22. Porogadus guentheri Jordan & Fowler, 1902; 22A–B, BSKU 86832, 255 mm SL, 32°18’N, 132°21’E, 1678–1690 m, head drawing; 22C–D, BSKU 47928, 32°26’N, 133°50’E, 1316–1542 m, otolith (C inner face, D ventral view); 22E–F, BSKU 86818, 251 mm SL, 32°24'N, 132°16'E, 1501–1516 m, otolith (E inner face, F ventral view); 22G, BSKU 86819, 248 mm SL, 32°18'N, 132°21'E, 1678–1690 m, otolith (inner face); 22H, BSKU 43444, 257 mm SL, 32°21'N, 132°27'E, 1642–1651 m, otolith (Inner face).

FIGURE 45. Geographic distribution of the species of the Porogadus trichiurus 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).