Porogadus trichiurus ( Alcock, 1890 )

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 : 57-60

Porogadus trichiurus ( Alcock, 1890)

Figs. 27–28 , 45 , 50 , Tab. 1–7

Dermatorus trichiurus Alcock 1890: 298 ; Alcock 1892: pl. 1, fig. 1.

Porogadus trichiurus: Nielsen et al. 1999: 86 .

Porogadus (Dermatorus) trichiurus: Nolf 1980: 91 : pl. 11 fig. 10 (otolith).

Material examined (9 specimens): AMS I.36456-009 (2 specimens), 162 and 172 mm SL, Philippines, Lagonoy Gulf, 13°21’19’’N 124°12’E, 1037–1100 m, 30 m otter trawl, collected by Dr. J. Paxton, 24. September 1995; CAS 83066 (2 specimens), 230 and 144 mm SL, (probably same location as AMS I.36456-009) ; MNHN 1994-0760 (4 specimens), 95–160 mm SL, 22°06’S 166°27’E, 1850 m, Biocal Expedition, Sta. cp27, collected by J. Charcot, 28 August 1985 ; SIO 03- 157, 158 mm SL, 23°01’N 66°01’E, Indian Ocean, off Karachi, trawl, 1677–1713 m, 14 October 2003 ; USNM 150720, 232 mm SL, off Omai Saki Light , Japan, 34°08’N 137°98’E, 1211 m , R / V Albatross , sta. D5082, 20 December 1906 .

Diagnosis. Precaudal vertebrae 15–17; long gill rakers on first gill arch 18–21, with very few intermittent patches; HL:HD 1.73–1.81; strong head spines: on ethmoidal, lacrimal, prefrontal, interorbital, supraorbital, sphenotic, supratemporal, inner and outer posttemporal, inner and outer preopercular rims, and 5th infraorbital; opercular spine weak, flat; maxilla without scales; small opercular flap with ridges on lower part; lower lateral line pores until beginning of anal fin 15; vomer with moderately broad dentition patch with 1–3 rows of teeth; palatines with moderately broad dentition patch 2–4 rows of teeth; otolith with single colliculum; OL:OH = 1.04–1.27; OL:TCL = 1.50–2.14.

Description (based on non-types). Meristics: precaudal vertebrae 15–17, 0–1 last vertebrae without ribs; pectoral-fin rays 16–18; D/V = 4–6; D/A = 22–26; V/A = 17–19; long gill rakers on lower first gill arch 18–21. Gill rakers in a typical specimen (USNM 150720) from off Japan, on lower first gill arch with five short rakers, followed by a series of 19 long rakers. The lower 9 of those intercept by plate shaped rakers. These are placed on the inner part of the gill arch and not directly between the long rakers. The long rakers are blade shaped, and armed with spinules. Upper gill arch with two plate shaped rakers, followed by a semi-long raker, a plate like raker, two semi-long rakers and two plate shaped rakers.

Morphometrics: in % of SL: HL 14.5–16.8; maximal HD 8.1–9.4; HD through center of eye 5.5–6.8; bony interorbital width 3.5–3.9; snout length 4.9–6.0; upper jaw length 8.9–10.6; predorsal 15.3–17.0; preanal 27.5–29.6; prepelvic 11.6–12.3; prepectoral 15.2–17.5; pectoral length 9.4 (single specimen). Relations: HL:HD = 1.73–1.81; HL to snout length 2.60–2.98; preanal to predorsal 1.71.187; predorsal to prepectoral 0.97–1.09.

Slender fish with long tapering tail and moderately long snout. Maximal size of fishes investigated 172 mm SL. Head moderately long and moderately slender, with flat to slightly convex dorsal profile, with few strong spines and ridges as follows: ethmoidal (1), lacrimal (ridge and 1 spine), prefrontal (1 weak), interorbital (1–3), supraorbital (2–3), sphenotic (2), supratemporal (1–2), inner and outer posttemporal (2–3), inner preopercular rim (4–5), outer preopercular rim (2–3 weak), and on 5th infraorbital (1–3). Opercle with short, weak spine and flat base. Eye relatively 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 between occiput and sphenotic and supraorbital spines and on occiput in front of nape, the latter with 1 or 2 bilateral symmetrical openings (pores or damaged thin skin cover?). Head squamation on opercle, cheeks, and occiput, few scales around eye, scales absent on maxilla and frontal. Opercle with two to three moderately sized neuromasts behind preopercular edge; opercular flap small, with radial ridges on lower third. Lateral line rows rarely well visible and therefore number of pores countable only in rare instances. Upper lateral apparently very long with 22 pores, and lower lateral line row with 15 pores until beginning of anal fin in one specimen.

Dentition.All teeth tiny and cone-shaped. Vomer with a narrow and short dentition patch with 1–3 rows of teeth anteriorly, naked posteriorly; palatines with a short and narrow dentition patch with 2–4 rows of teeth in middle part. Premaxilla tooth patches not fused anteriorly; ca. 5 teeth rows anteriorly and 2–3 rows posteriorly. Dentary tooth patches not fused anteriorly; 3–4 teeth rows anteriorly and a single row posteriorly. Median basibranchial tooth patch short.

Otolith morphology (n = 6). Size up to 2.5 mm in length; OL:OH = 1.04–1.27; OH:OT = 2.2–3.5. Variably thick and relatively compressed otoliths with roundish to oval outline. Anterior and posterior rims blunt, rounded. Dorsal rim high, rounded, ventral rim moderately deep, somewhat irregularly rounded. All rims smooth. Inner face nearly flat, smooth, with long, centrally positioned sulcus reaching relatively close to anterior and posterior rims of otolith; OL:TCL = 1.50–2.14. Sulcus shallow, undivided, with broad and shallow colliculum. Dorsal field with large indistinct depression; ventral field smooth, sometimes with faint ventral furrow close to ventral rim of otolith. Outer face smooth, with mild, anteriorly positioned umbo.

Coloration. Live coloration not known. Color of preserved specimens with light brown body and dark brown head, and opercle particularly dark.

Discussion. Alcock (1890) described Porogadus trichiurus based on a unique type housed at ZSI which was not available for review. His description is not very detailed, but the long gill raker count (20), pectoral fin count (16) and proportion of the head deduced from his detailed drawing ( Alcock 1892) of a ratio of HL:HD of about 1.7 support the observations made with the specimens here described as P. trichiurus . Specimens described by Norman (1939) from the northeastern Indian Ocean as P. trichiurus have fewer long gill rakers (15) and a more slender head (HL:HD of nearly 2.0) and are here placed in Porogadus dracocephalus (see above).

Within the Porogadus trichiurus group, P. trichiurus shares with P. guentheri the relatively intense and many spines on the head and the head proportions, but differs in the larger predorsal length (15.3–17.0 vs 13.7–14.7), the presence of scales on occiput and around the eye and lack of scales on maxilla, and the distinctly more compressed otolith (OL:OH = 1.04–1.27 vs 1.45–1.64). It differs from most other Porogadus species by the position of the intermittent plates between the long gill rakers close to the inner side and not directly between the long rakers. This organization is probably a common trait for the Porogadus trichiurus group except for P. solomonensis .

Distribution. Porogadus trichiurus apparently is widely distributed in the western Pacific and has here been identified from southern Japan, eastern Philippines and off New Caledonia. The type specimen and one specimen described here stem from the northern Indian Ocean off the western coast of India. It occurs in moderate depth between 1037 and 1850 m and seems to stay close to the shelf break, i.e., not further away than 100 km.

Figures

FIGURE 27. Porogadus trichiurus (Alcock, 1890), AMS I.36456-009, 162 mm SL, 13°21’N, 124°12’E, 1037–1100 m, (A–B photographs, C x-ray photograph).

FIGURE 28. Porogadus trichiurus (Alcock, 1890); 28A–B, CAS 83066, 230 mm SL, Philippines, Lagonoy Gulf, 1037–1100 m, head drawing; 28C–D, AMS I.36456-009, 162 mm SL,13°21’N, 124°12’E, 1037–1100 m, head drawing; 28E, SIO 03-157, 158 mm SL, 23°01'N, 66°01'E, 1677–1713 m, head drawing; 28F–G, CAS 83066, 230 mm SL, Philippines, Lagonoy Gulf, 1037–1100 m, otolith (F inner face, G ventral view); 28H–I, SIO 03-157, 158 mm SL, 23°01'N, 66°01'E, 1677–1713 m, otolith (H inner face, I ventral view); 28L–M, AMS I.36456-009, 162 mm SL, 13°21’N, 124°12’E, 1037–1100 m, otolith (L inner face, M ventral view); 28N–O, MNHN 1994-0760, 160 mm SL, 22°06’S, 166°27’E, 1850 m, otolith (N inner face, O ventral view).

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).