Porogadus longiceps Garman, 1899

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 : 34-38

Porogadus longiceps Garman, 1899

Figs. 3 , 13–14 , 44 , 49 , Tab. 1–7

Porogadus longiceps Garman, 1899: 153 , pl. F, fig. 2, pl. 76, fig. 1; Nielsen et al. 1999: 86; Castellanos-Galindo et al.

2006:199.

Material examined ( 7 specimens): Lectotype MCZ 28660, 405 mm SL, off Panama, 04°56’N 80°52’W, 3240 m, R / V Albatross , large beam trawl, 6 March 1891; paralectotypes: MCZ 28661, 258 mm SL, off Panama, 07°15’N 79°36’W, 1865 m, R / V Albatross , large beam trawl, 10 March 1891; MCZ 28662, 130 mm SL, 05°36’N 86°56’W, 245 m, R / V Albatross , 28 February 1891; non-types: SIO 89-30, 476 mm SL, R / V Thomas Washington, sta. 69, dredge, collected by Mr. R. Comer, 10°20’N 103°39’W, 2644 m, 29 February 1988; SIO 72-108 - 61, 410 mm SL, R / V Thomas Washington, 00°48’N 86°09’W, caught at surface with dipnet, collected by Mr. M. Elston & party, 26 June 1972; CAS ( SU) 68833, 198 mm SL, 60 miles south of Isla del Coco, 04°50’N 87°00’W, collected by William Beebe and John Tee-Van, no depth information, 30 May 1925; tentatively assigned specimen (syntype): MCZ 28659, 465 mm SL, off Panama, 06°21’N 80°41’W, 3279 m, large beam trawl, 7 March 1891.

Diagnosis. Precaudal vertebrae 17–19; long gill rakers on lower first gill arch 11–13; pectoral-fin rays 19–22; HL:HD 1.81–2.08; head spines strong in small specimens, short and poorly extruding in large specimens, present on ethmoidal, lacrimal, prefrontal (weak), interorbital (weak), supraorbital (weak in large specimens), sphenotic, 5th infraorbital, supratemporal (absent in large specimens), inner and outer posttemporal (absent in large specimens), inner and outer preopercular rims (absent in large specimens); opercular spine sharp, strong, extruding; maxilla with no or few scales at rear; lower lateral line pores until beginning of anal fin 22–24; vomer with broad dentition patch (3–9 rows of teeth); palatines with broad dentition patch (2–11 rows of teeth); otolith with separate ostial and caudal colliculi indicated by ventral incision; OL:OH = 1.75–2.1; OL:TCL = 1.8–1.9.

Description. Meristics: precaudal vertebrae 19 (17–19), 1 (0–1) last vertebrae without ribs; pectoral-fin rays 20 (19–22, 17– 18 in tentatively assigned specimen); D/V = 6 (5–7); D/A = 28 (25–28); V/A = 20 (19–21); long gill rakers on lower gill arch 11 (11–13). Gill rakers in lectotype on lower first gill arch with eight plate-shaped rakers, followed by a series of 11 long rakers. The lower seven of those intercepted by single plate shaped rakers. Upper gill raker with a series of three plate shaped and three slightly longer rakers intercepted.

Morphometrics: in % of SL: HL 17.5 (16.9–18.5); maximal HD 10.0 (8.1–10.1); HD through center of eye 6.7 (5.3–6.7); bony interorbital width 3.7 (3.3–3.9); snout length 5.8 (5.2–6.9); upper jaw length 10.1 (9.8–11.0); predorsal 19.4 (17.7–19.4); preanal 33.5 (33.0–37.0); prepelvic 15.0 (14.2–16.3); prepectoral 19.0 (17.3–20.2); pectoral length 10.1 (9.7–11.4). Relations: HL:HD = 1.81 (1.81–2.08, 1.72 in tentatively assigned specimen); HL to snout length 3.12 (2.93–3.52); preanal to predorsal 1.73 (1.73–2.01); predorsal to prepectoral 1.02 (0.97–1.11).

Slender fish with long tapering tail and long, pointed snout. Maximal size of fishes investigated 476 mm SL. Head long and slender, with flat dorsal profile, with strong spines in small specimens (<200 mm SL) and decreasing in length and strength or absent in large specimens (> 400 mm SL) as follows: ethmoidal (1), lacrimal (ridge with 1 spine), prefrontal (1 weak), interorbital (2–3, weak in large specimens), supraorbital (2, absent in large specimens), sphenotic (2–3), 5th infraorbital (2), supratemporal (2, absent in large specimens), inner and outer posttemporal (3–5, 1 in large specimens), inner preopercular rim (3, none in large specimens), outer preopercular rim (3–4, absent in large specimens). 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, 1 or 2 pores on occiput along inner edges of temporal spines. Head squamation on opercle, cheeks, occiput, frontal, snout (in small specimens), small scales in around eyes, maxilla without scales in large specimens, with small scales on rear part in small specimens. Opercle with one to three distinct large neuromasts behind preopercular edge; opercular flap very small, fully covered by scales, without radial ridges. All three lateral line rows well visible. The lectotype (MCZ 28660) is particularly remarkable for a good exposure of the lateral line pores, which is used for Fig. 3 . Upper lateral line row with 10–11 pores ( Garman 1899 figures many more pores); lower lateral line row with 22–24 pores until beginning of anal fin (22 in figure of Garman 1899); central lateral line row long, lower and central lateral line rows fading behind beginning of anal fin.

Dentition. All teeth tiny and cone-shaped or flattened. Vomer with a broad dentition patch with 5–9 rows of teeth anteriorly in specimens> 400 mm SL and 3–4 rows in specimens <250 mm SL; palatines with broad dentition patch with 7–11 rows of teeth throughout in specimens> 400 mm SL and 2–5 rows in specimens <260 mm SL. Premaxilla tooth patches not fused anteriorly; up to 14 teeth rows anteriorly and 4–5 rows posteriorly. Dentary tooth patches not fused anteriorly; up to 10 teeth rows anteriorly and 3–4 rows posteriorly. Median basibranchial tooth patch long and wide.

Otolith morphology (n = 4). Size up to 7.2 mm in length (lectotype); OL:OH = 1.75–2.1 (1.45 in tentatively assigned specimen; Fig. 14H ); OH:OT c.2.6. Thin, elongate otolith, anteriorly rounded, posteriorly slightly expanded. Dorsal with broadly rounded predorsal lobe, ventral rims regularly curving. All rims smooth. Inner face slightly convex, smooth, with moderately long, centrally positioned sulcus; OL:TCL = 1.8–1.9. Sulcus with shallow, poorly divided colliculi (fused in tentatively assigned specimen; Fig. 14H ), but separation into ostium and cauda always marked by indentation of ventral margin. Dorsal and ventral fields rather smooth. Outer face smooth, with weak central umbo.

Coloration. Live coloration not known. Color of preserved specimens medium to reddish brown; head slightly darker than body, opercle distinctly darker.

Variability and ontogeny. A large syntype (MCZ 28659) is only tentatively placed in P. longiceps because it somewhat differs from the other specimens in the shorter head expressed in a lower HL:HD ratio of 1.72 (vs 1.81–2.08), the lower number of pectoral-fin rays (17–18 vs 19–22), and the compressed, rather thick otolith (OL: OH = 1.45 vs 1.75–2.1) with fused colliculi and no predorsal lobe ( Fig. 14H–J ). MCZ 28659 is a large specimen and it is possible that all the observed differences may still fall within the variability of P. longiceps but this would considerably stretch the diagnosis. It is also possible that some of the differences represent pathological deformations, for instance in the otolith morphology. In any case and before further specimens have become available for study we consider MCZ 28659 as tentatively assigned only .

Porogadus longiceps is also known for a distinctive and large degree of late ontogenetic changes. Garman (1899) noted that small specimens had much more intense spines on the head than large ones even to the extent that some spines totally disappear in large specimens. We confirm Garman’s observation (see above description of spines) and further observe that the otolith of small specimen of 258 mm SL (MCZ 28661; not figured) is considerably more elongate than those of the larger specimens (MCZ 28660 and SIO 89-30; Figs. 14E–G ) (OL:OH 2.1 vs 1.75–1.85). Other aspects affected in late ontogeny are the rows of teeth on vomer, palatines and premaxilla. Specimens larger than 400 mm SL have 5–9 rows of teeth on the vomer, 7–11 rows on the palatines and 11–14 rows on the premaxilla, while specimens smaller than 260 mm SL show 2–4 rows of teeth on the vomer, 2–5 rows on the palatines and 4–8 rows on the premaxilla. The number of teeth on the dentary ranges from 3 to 10 rows of teeth and also appears to be increasing with size, but with a less clear trend. No comparable late ontogenetic changes have been observed in any of the other Porogadus species including the similarly large growing P. miles .

Discussion. MCZ 28660 was selected as lectotype on the basis that it is the best preserved of the large syntypes and that it likely represents the specimen figured by Garman (1899; plate F, Fig. 2 ). Porogadus longiceps is the largest growing species of all Porogadus species together with P. miles and is very similar to P. miles differing mainly in the lower number of long gill rakers (11–13 vs 14–18) and the reduced intensity of spines on the head in large specimens. It differs from all other species of the Porogadus miles Group except P. mendax n. sp. and P. miles in the higher number of lower lateral line pores until the beginning of the anal fin (22–24 vs 16–21) and, except P. turgidus in the distinction of ostium and cauda of the sulcus. From P. mendax it differs further in the small opercular flap without ridges (vs large with ridges) and from P. turgidus further in the predorsal length (17.7–19.4 vs 15.7) and the preanal length (33.0–37.0 vs 29.6–30.5). We assume that P. longiceps has derived from a stock of the widespread P. miles that became isolated in the tropical eastern Pacific at some time.

Distribution. Porogadus longiceps is geographically restricted to a relatively small area off the tropical eastern Pacific chiefly between 10°N and the equator, and ventures out for about 800 km from the continental break. It occurs at depth primarily between 1800 and 3300 m but two specimens are caught in very shallow water at 245m or near the surface. No other species of Porogadus has been caught substantially shallower than 1000 m. The reason for the unusual shallow catches of this otherwise deep dwelling species are not known.

Figures

FIGURE 2. Panel of comparative head drawings: from top to bottom: Porogadus (P. miles), Tenuicephalus (T. squamilabrus n. sp.) and selected putative related genera; Alcockia (A. rostrata), Bathyonus (B. laticeps) and Penopus (P. microphthalmus).

FIGURE 3. Lateral line system in Porogadus. Photograph of fish and drawings of opercular neuromast is from P. longiceps, drawings of scales are from P. dracocephalus n. sp.

FIGURE 13. Porogadus longiceps Garman, 1899; 13A–C, MCZ 28660, lectotype, 405 mm SL, 04°56’N, 80°52’W, 3240 m; 13D, MCZ 28661, paralectotype, 258 mm SL, 07°15’N, 79°36’W, 1865 m.

FIGURE 14. Porogadus longiceps Garman, 1899; 14A–B, MCZ 28660, lectotype, 405 mm SL, 04°56’N, 80°52’W, 3240 m, head drawing; 14C–D, MCZ 28661, paralectotype, 258 mm SL, 07°15’N, 79°36’W, 1865 m, head drawing; 14E–F, MCZ 28660, lectotype, 405 mm SL, 04°56’N, 80°52’W, 3240 m, otolith (E inner face, F ventral view); 14G, SIO 89-30, 476 mm SL, 10°20’N, 103°39’W, 2644 m, otolith (inner face); 14H–J, MCZ 28659, tentatively assigned specimen (syntype), 465 mm SL 06°21’N, 80°41’W, 3279 m, otolith (H inner face, I anterior view, J 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).