Porogadus mendax, 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 : 38-41

Porogadus mendax n. sp.

Figs. 15–16 , 44 , 49 , Tab. 1–7

Material examined ( 2 specimens): Holotype BMNH 1996.2 .14.31, 290+ mm SL, 31°18’N 16°47’W, 4435–4457 m, R. R. S. Discovery Cruise semi-balloon otter trawl, 07 October 1995, collected by N. Merrett; paratype BMNH 1995.11 .22.4, 287 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 18; long gill rakers on first gill arch 13–14; HL:HD 1.89–1.92; all head spines strong, present on ethmoidal, lacrimal, prefrontal, interorbital, supraorbital, sphenotic, 5th infraorbital, supratemporal, inner and outer posttemporal, inner and outer preopercular rims; opercular spine sharp, strong, extruding; additional (3rd) postorbital pore, many cavities and/or pores on top of head; maxilla without scales; large opercular flap with ridges; lower lateral line pores until beginning of anal fin 22–23; vomer with broad dentition patch (5–7 rows of teeth); palatines with broad dentition patch (9 rows of teeth); otolith with single, uniform colliculum; OL: OH = 1.85–2.05; OL:TCL = 2.15–2.3.

Description. Meristics: precaudal vertebrae 18 (18), 1 (1) last vertebrae without ribs; pectoral-fin rays 18 (18); D/V = 5 (5); D/A = 24 (24–25); V/A = 19 (19); long gill rakers on first gill arch 13 (13–14). Gill rakers in Holotype on lower first gill arch with nine plate-shaped rakers, followed by a series of 13 long rakers. The lower seven of those intercepted by single plate shaped rakers. Upper gill raker with a series of two plate shaped and three slightly longer rakers intercepted, followed by two slightly longer rakers and two short rakers.

Morphometrics: in % of SL: HL 15.5 (15.5–15.7); maximal HD 8.1 (8.1–8.3); HD through center of eye 5.1 (5.1–5.7); bony interorbital width 2.7 (2.7); snout length 4.7 (4.7–5.3); upper jaw length 8.6 (8.5–8.6); predorsal 17.8 (17.4–17.8); preanal 31.1 (30.6–31.1); prepelvic 12.5 (12.5–13.0); prepectoral 15.8 (15.8–16.3); pectoral length 10.2 (10.1–10.2). Relations: HL:HD = 1.92 (1.89–1.92); HL to snout length 3.29 (2.96–3.29); preanal to predorsal 1.75 (1.75–1.76); predorsal to prepectoral 1.13 (1.06–1.13).

Slender fish with long tapering tail and long, pointed snout. Maximal size of fishes investigated 290+ mm SL. Head long and slender, with slightly concave dorsal profile, with strong spines as follows: ethmoidal (1), lacrimal (ridge with 1 spine or up to 4 individual spines), prefrontal (1), interorbital (3), supraorbital (1–2), sphenotic (2–3), 5th infraorbital (2), supratemporal (1–2), inner and outer posttemporal (3–4), inner preopercular rim (3–5), outer preopercular rim (1–3, variable in strength). 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 along inner edges of temporal spines in front of nape and cavernous system extending between squamation of occiput and sphenotic and supraorbital spines and thin skin cover apparently easily affected by fish recovery and then giving impression of open pores ( Fig. 16D ). Head squamation on opercle, cheeks, occiput, frontal, and in front of and above eyes, area behind eyes, snout and maxilla without scales. Opercle with two to three distinct large neuromasts behind preopercular edge; opercular flap very large, with radial ridges along lower margin. All three lateral line rows reasonably well visible. Upper lateral line row with 7–8 pores; lower lateral line row with 22–23 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 or flattened. Vomer with a broad dentition patch with 5–7 rows of teeth; palatines with wide dentition patches with nine rows of teeth. Premaxilla tooth patches, narrow, not fused anteriorly; ca. eight teeth rows anteriorly and very narrow with 1–2 rows posteriorly. Dentary tooth patches not fused anteriorly; ca. 5 teeth rows anteriorly and 1–2 rows posteriorly. Median basibranchial tooth patch short, anteriorly widened.

Otolith morphology (n = 2). Size up to 6.5 mm in length (holotype); OL:OH = 1.85–2.05; OH:OT = 2.1–2.4. Thin, elongate otolith, anteriorly and posteriorly rounded, posteriorly slightly expanded. Dorsal rim with broadly rounded predorsal lobe, ventral rim shallow, regularly curved. All rims smooth. Inner face slightly convex, smooth, with short, centrally positioned sulcus; OL:TCL = 2.15–2.3. Sulcus with shallow, undivided, uniform, oval colliculum. Dorsal field with small, indistinct depression; ventral field with faint ventral furrow close to otolith rim in central portion, anteriorly and posteriorly turning upwards to near terminations of sulcus. Outer face smooth, relatively flat.

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

Discussion. Porogadus mendax is similar to P. miles and the co-occurring P. caboverdensis and P. turgidus . The external differences to P. miles are subtle and depending on good preservation (see also to P. miles ). Porogadus mendax has no scales on the maxilla (vs scales on the rear part of the maxilla), has 3 postorbital pores (vs 2), and an extensive cavernous system on the top of the head that P. miles does not show. The most reliable and secure character for distinction is the otolith, when preserved, which in P. mendax shows an undivided, relatively short colliculum (OL:TCL = 2.15–2.3), while P. miles always shows clearly distinguished ostial and caudal colliculi and a relatively long sulcus (OL:TCL = 1.7–1.9). Porogadus mendax differs from P. caboverdensis and P. turgidus in the higher number of lower lateral line pores until the beginning of the anal fin (22–23 vs 16–20), the absence of scales on the maxilla, and the otolith, which in P. caboverdensis is considerably more compressed (OL:OH = 1.85–2.05 in P. mendax vs 1.05–1.5 in P. caboverdensis ) and in P. turgidus shows a clear separation of ostial and caudal colliculi. From P. caboverdensis it differs further in the broad vomer with 5–7 rows of teeth (vs narrow with 1–3, rarely 4 rows).

Distribution. Porogadus mendax is one of three deepwater species of the genus occurring in the Cape Verde and adjacent Canary Basins of the northeastern Atlantic (the other two being P. caboverdensis and P. turgidus ). It has been caught at depths between 4435 and 4610 m.

Etymology. From mendax (Latin) = liar, narrator, referring to its close similarity to the common P. miles , which, however, does not seem to occur at depth exceeding 4000 m.

Figures

FIGURE 15. Porogadus mendax n. sp., BMNH 1996.2.14.31, holotype, 290+ mm SL, 31°18’N, 16°47’W, 4435–4457 m.

FIGURE 16. Porogadus mendax n. sp.; 16A–B, BMNH 1996.2.14.31, holotype, 290+ mm SL, 31°18’N, 16°47’W, 4435–4457 m, head drawing; 16C–D, BMNH 1995.11.22.4, paratype, 287 mm SL 20°55’N, 31°11’W, 4500–4610 m, head drawing; 16E–F, BMNH 1996.2.14.31, holotype, 290+ mm SL, 31°18’N, 16°47’W, 4435–4457 m, otolith (E inner face, F ventral view); 16G–H, BMNH 1995.11.22.4, paratype, 287 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).