Porogadus miles Goode & Bean, 1885

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 : 42-46

Porogadus miles Goode & Bean, 1885

Figs. 1–2 , 4 , 6 , 17–19 , 44 , 49 , Tab. 1–7

Porogadus miles Goode & Bean 1885: 602 ; Günther 1887: 113; Goode & Bean 1895: 334, fig. 292; Jordan & Evermann 1898: 2520; Grey 1956: 211 (see there for further citations); Grey 1958: 175; Shcherbachev 1980: 89, figs. 19–20; Nolf 1980: 91, pl. 11 fig. 7 (otolith); Schwarzhans 1981: 94, fig. 91 (otolith); Carter 1984: 2–183; Carter & Sulak 1984: 376, fig. 6c; Machida & Amaoka 1990: 64, fig. 2, 3(?); Nielsen et al. 1999: 86, fig. 83; Fahay 2007: 692, figs. p. 693 A–C; Mincarone et al. 2008: 55, fig. 3S; Shinohara et al. 2009: 707.

Porogadus nudus Vaillant 1888: 262 , pl. 24, figs. 2–2b; Nybelin 1957: 291, textfig. 21; Machida & Amaoka 1990: 67, Fig. 4 ; Nielsen et al. 1999: 86.

Porogadus sp. : Prokofiev 2005: 116, figs. 7–8.

? Porogadus sp. 2 : Shcherbachev 1980: 88, fig. 18 (described here as Porogadus aff. miles ).

Material examined ( 34 specimens): Holotype USNM 35625, 145 mm SL, 38°45’N 73°03’W, 2136 m, Albatross Expedition 1883-1900, Sta. D 2230, large beam trawl, 12 September 1884; holotype of P. nudus MNHN 86-537, 198 mm SL, 20°30’N 16°32’W, 2321 m, R / V Talisman, 1883; paratype of P. nudus MNHN 86-536, 136 mm SL, 16°N 24°W, 3200 m, R / V Talisman, 1883; BMNH 2017.5 .11.83, 272 mm SL, 15°04’N 18°34’W, 2970–2990 m, R. R. S. Discovery Cruise semi-balloon otter trawl, collected by Institute of Oceanographic Sciences, 06 August 1983; BSKU 35715, 354 mm SL, 38°44-46’N 143°11-12’E, 1950–1960 m, R / V Tansei-Maru, 3 m beam trawl, coll. Okamura, 25 July 1981; BSKU 98881, 167 mm SL, 01°59’S 157°12’E, 1610 m, R / V Hakuho-maru, 3 m beam trawl, 4 Jan. 1968; BSKU 116117-120 (1 of 5 specimens), 276 mm SL, 34°52’N 139°27-30’E, 1525–1685 m, R / V Tansei-maru, beam trawl, 17 Dec. 1982; BSKU 127724 (otolith only), 38°47-48’N 143°13-14’E, 2090–2120 m, R / V Hakuho-maru, beam trawl, 13 Aug. 1967; Dimitry Mendeleev (otolith only), 234 mm SL, St. 1542; FAKU 47604, 233 mm SL, 21°10’N 176°28’E, 1281 m; MCZ 57618 (otolith only), 38°58’N 69°50’W, 2903 m, R / V Oceanus 093, 41’ GMT, collected by Richard L. Haedrich, 31 March 1981; MCZ 59143, 340 mm SL, 38°41’N 70°49’W, 2960–2980 m, R / V Oceanus 043, 41’ GMT, collected by Richard L. Haedrich, 15 April 1978; MCZ 146877, 275 mm SL, 39°35’N 70°32’W, 2290–2300 m, R / V Atlantis II 086, 41’ GMT, collected by Richard L. Haedrich, 18 March 1975; MCZ 167870 (otolith only), 39°37’N 69°31’W, R / V Delaware II 08-04, 30 March 2008; MNHN 1976-0059 , 132 mm SL, 00°45’N 08°27’E, 2231 m, Walda Expedition , Sta. 32cy23, collected by J. Charcot, 02 August 1971; MNHN 2004- 1327, 282 mm SL, 05°49’S 09°42’E, 3172–3193 m, R / V Atalante , Biozaire 3 Expedition , Sta. cp16, 28 December 2003; USNM 135626, 343 mm SL, Albatross, ND; USNM 316573 (otolith only), 38°45’N 72°39’W, 2110–2160 m, R / V Oceanus , Aslar Expedition , Cruise Ma-5, Sta. 4, 04 August 1985; ZMUC P2397222-223 , R / V Vityaz 2639 (2 specimens), 257–274 mm SL, 25°07’S 36°49’E, 2140–2230 m, 26 November 1988; ZMUC P2397224 , R / V Vityaz sta. 2673, 265 mm SL, 32°45’S 45°31’E, 2100–2400 m, 9 December 1988; ZMUC P2397225 , R / V Vityaz sta. 2772, 185 mm SL, 31°59’S 45°11’E, 1950–2050 m, 25 December 1988; ZMUC P2397226 , R / V Vityaz 2779, 165 mm SL, 30°30’S 46°53’E, 2580–2680 m, 26 December 1988; ZMMGU 14411, 298 mm SL, R / V Zvezda Kryma , Cruse 6, trawl 52, 34°08’S 44°12’E, 1500–1560 m, 21 July 1976; ZMUC P 77587, 182 mm SL, 38°50’N 72°34’W, 2196 m, 16 May 1974; ZMUC P 77588, 322 mm SL, 37°03’N 74°07’W, 2150 m; ZMUC P 77595, 214 mm SL, 39°33’N 70°43’W, 2379–2416 m, 10 July 1975; ZMUC P 2397155, 229 mm SL, Galathea 2 expedition, sta.474, ST 300 – 3 m wide sledge trawl,, Sunda Trench , 09°49’S 114°13’E, 3810–3840 m, 11 September 1951; ZMUC P2397156-57 , (2 specimens), 205+ and 259 mm SL, Galathea 2 expedition, sta.299, herring otter trawl, Bay of Bengal , 17°10’N 84°30’E, 2820 m, herring otter trawl, 24 April 1951; Porogadus aff. miles: MNHN 1995 -0948, 387 mm SL, 14°49’S 167°15’E, 1360 m R / V Alis , Musorstom 8 Expedition , Sta. cp1110, 08 October 1994; ZMMGU 15171 (otolith only), 312 mm SL, R / V Prof. Mesyatzev, Cruse 7, trawl 45,16°55’S 114°53’E, 1600–1700 m, 24 April 1979.

Diagnosis. Precaudal vertebrae 17–19; long gill rakers on first gill arch 14–18; HL:HD 1.81–2.03; 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; maxilla with scales; small opercular flap with ridges; lower lateral line pores until beginning of anal fin 23–26; vomer with broad dentition patch (3–5 rows of teeth); palatines with broad dentition patch (4–9 rows of teeth); otolith with separate ostial and caudal colliculi; OL:OH = 1.55–1.9; OL:TCL = 1.7–1.9.

Description. Meristics: precaudal vertebrae 18 (17–19), 1 (0–2) last vertebrae without ribs; pectoral-fin rays 18 (17–21); D/V = 6 (5–7); D/A = 26 (24–30); V/A = 19 (18–21); long gill rakers on lower first gill arch 15 (14–18; 11 in Porogadus aff. miles, MNHN 1995 -0948). Gill rakers in a typical specimen (MCZ 59143) on lower first gill arch with eight plate-shaped rakers, followed by a series of 17 long rakers. The lower 12 of those intercepted by single plate shaped rakers, broad and placed right between the long rakers. Upper gill arch with a serie of six plate shaped and three semi-long rakers intercepted.

Morphometrics: in % of SL: HL 15.9 (15.6–17.6); maximal HD 8.1 (8.1–9.5); HD through center of eye (5.4– 6.3); bony interorbital width (2.8–4.1); snout length 4.8 (4.8–6.4); upper jaw length 9.4 (9.4–10.2); predorsal 16.6 (16.6–20.3); preanal 29.9 (29.9–36.0); prepelvic (12.7–15.6); prepectoral (16.4–18.5); pectoral length (7.4–11.0). Relations: HL:HD = 1.95 (1.81–2.03); HL to snout length 3.29 (2.68–3.29); preanal to predorsal 1.81 (1.62–1.89); predorsal to prepectoral (0.99–1.16).

Slender fish with long tapering tail and long, pointed snout. Maximal size of fishes investigated 387 mm SL. Head long and slender, with flat dorsal profile, with strong spines as follows: ethmoidal (1), lacrimal (ridge or up to 3 individual spines), prefrontal (1), interorbital (3–4), supraorbital (2–3), sphenotic (2–4), 5th infraorbital (1–3), supratemporal (1–2), inner and outer posttemporal (2–4), inner preopercular rim (3–5), outer preopercular rim (1–3, variable in strength). Opercle with sharp, strong, extruding spine. Eye moderately sized 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 2 pores, head top with 1–2 pores on occiput along inner edges of temporal spines in front of nape. Head squamation on opercle, cheeks, occiput, frontal, snout, around eyes, and rear part of maxilla. However squamation on anterior part of head and on maxilla often indiscernible or lacking because of deciduous nature or preservation (see Figs. 18C–D, F ). Opercle with two to three distinct large neuromasts behind preopercular edge; opercular flap small to mederately large, with radial ridges along lower margin. All three lateral line rows reasonably well visible. Upper lateral line row with 9–11 pores, sometimes expanded and then up to 16 pores; lower lateral line row with 23–26 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 narrow dentition patch in the entire length with 3–5 rows of teeth anteriorly; palatines with moderately broad to broad dentition patch with 4–9 rows of teeth in the middle part. Premaxilla tooth patches not fused anteriorly; 8–12 teeth rows anteriorly and 4–5 rows posteriorly. Dentary tooth patches not fused anteriorly; 4–7 teeth rows anteriorly and 1–2 rows posteriorly. Median basibranchial tooth patch short to moderately long, wide.

Otolith morphology (n = 18). Size up to 8.4 mm in length (in Porogadus aff. miles, MNHN 1995 -0948); OL: OH = 1.55–1.9; OH:OT = 3.0–3.7. Thin, elongate otolith, anteriorly with inferior rounded projection and posteriorly rounded and expanded. Dorsal rim with broadly rounded predorsal lobe, ventral rim shallow, regularly curved. All rims smooth or dorsal rim slightly undulating. Inner face slightly convex, smooth, with moderately long, centrally positioned sulcus; OL:TCL = 1.7–2.1. Sulcus with shallow, distinctly separated ostial and caudal colliculi; length ostial to caudal colliculum very variable, ranging from 1.4 to 2.1. Dorsal field with indistinct depression; ventral field with faint ventral furrow close to otolith rim. Outer face smooth, relatively flat to slightly convex.

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

Variability. Despite some remaining uncertainties in the delimitation of the species, the abundance of specimens and data of P. miles allows for a reasonable analysis of the intraspecific variability. Characters which are here considered useful for differentiation of species and showing a narrow range of variability are: precaudal vertebrae (17–18), pectoral-fin rays (18–21), HL in % of SL (15.9–17.6), HL:HD (1.81–2.03), the number of lower lateral line pores until the beginning of the anal fin (23–26), the occurrence of most head spine patches and lateral head pores, and the status of the colliculi in the sulcus of the otolith. Characters with a moderate range of variability (not considering the two aff. specimens) are: long gill rakers (14–18), expression of head spines and exact numbers, width of vomer and palatine, snout (4.8–6.4 % SL) and upper jaw lengths (9.3–10.2 % SL), predorsal (17.3–20.3 % SL) and preanal lengths (29.9–36.0 % SL), the ratio OL:OH (mostly 1.79–1.98 but with specific excursions, see below), and the ratio OL:TCL (1.7–2.1). These variability ranges may serve as bench marks for assessments of less common species in the Porogadus miles Group. Other useful characters such as head squamation, pectoral fin length, or number of pores on the top of the head require particularly good preservation of specimens. This restricts both its values for identification as well as recognition of variability ranges.

Comparison with previously published counts and measurements. Certain counts and measurements have been published, which we are not able to verify. Carter & Sulak (1984) gave a range of 14 to 16 pectoral-fin rays (16 for the holotype) based on 18 specimens. Our recount of the pectoral-fin rays of the holotype was 18 and we counted a range of 17 to 21 pectoral-fin rays based on 20 specimens. This is in line with the counts published by Shcherbachev (1980; 19–20), Machida & Amaoka (1990; 17–19), and Prokofiev (2005; as Porogadus sp. ; 17–18), but not Grey (1958; 16). The type specimens of P. nudus were counted with 20 and 21 pelvic-fin rays. Ranges of pectoral-fin rays given by Carter & Sulak (1984) for syntypes of P. longiceps (19–20) and P. catena (15–17) are in line with our counts, but for syntypes of P. atripectus (16–18 vs 17–20), holotype of P. gracilis (14 vs 16) and holotype of P. abyssalis (18 vs 19 in Nybelin, 1957) are not and suggest a systematic difference in the method of counting. The preservation of the pectoral fins is often poor. We found high resolution x-rays to be of much help also for counting pectoral-fin rays.

The count of long gill rakers on the first gill arch is in line with counts given by Grey (1958; 15), Shcherbachev (1980; 14–15), Carter & Sulak (1984; 15), Machida & Amaoka (1990; 13–17), and Prokofiev (2005; as Porogadus sp. ; 16), but shows a larger variability than mostly recorded (14–18). The number of precaudal vertebrae (17–19) is in good agreement throughout literature.

Measurements are given by Carter & Sulak (1984) in % of GPL, which we found less indicative than in % of SL, even though this method somewhat restricts the number of usable measurements. Measurements given by Machida & Amaoka (1990) for the type specimen of P. miles and one other specimen also studied here are well aligned. The same is apparently true for selected measurements given by Shcherbachev (1980) and Prokofiev (2005; for Porogadus sp. ).

Discussion. Porogadus miles is the most commonly recorded and apparently most widely distributed species of the genus. It has been recorded throughout the tropical and subtropical Atlantic Ocean, from certain regions of the Indian Ocean and from the western Pacific off Japan and as far east as the Necker Ridge and the Emperor Seamounts west of Hawaii. The delimitation of P. miles however still remains somewhat uncertain. Porogadus miles was first described by Goode & Bean (1885) based on a single, relatively small specimen (145 mm SL) from the northwestern Atlantic. Vaillant (1888) described P. nudus from the northeastern Atlantic based on two specimens (the holotype being 198 mm SL and the paratype 136 mm). Vaillant noted only a few differences. e.g., in the range of lateral pores, pectoral fin length and head length, which he regarded as not very important and easily affected by preservation of the specimens concerned. The key character in his assessment to distinguish P. nudus from P. miles was the distance of the pelvic fin base to the anus being one fourth longer than the head length (vs being of equal length in P. miles ). We found that the ratio of the distance of the pelvic base to the beginning of the anal fin compared to the head length varies considerably within most well-defined species between just slightly under 1.0 to slightly over 1.3. We therefore consider this character to be of diagnostic value only in very few instances, i.e., in P. dracocephalus where it is the lowest measured and ranges from 0.72 to 0.98. Grey (1958) commented that “ P. nudus is closely related to P. miles and may prove to be the same species.” She considered the complete absence of lateral lines in P. nudus as the principal difference, which we cannot confirm after having reviewed both type specimens. Discernibility of the lateral line on the body in the Porogadus miles Group is often a matter of preservation. Machida & Amaoka (1990) reinvestigated the situation again and also studied the holotype of P. nudus . They concluded that the holotype of P. nudus does not show distinct lachrymal spines like the specimens of P. miles which they studied and considered this as the main distinctive character of the two species. Our study of several specimens of P. miles and P. nudus including the type series of both nominal species confirms that the holotype of P. nudus has a lachrymal ridge and no lachrymal spines (the paratype is too poorly preserved in that respect), while all other studied specimens indeed show 2 to 3 strong lachrymal spines. However, we also noted in several other species of the Porogadus miles Group that the status of the lachrymal may change from a ridge-like shape to a spinous appearance as part of an intraspecific variation and therefore do not regard this character as sufficient for distinguishing species on a stand-alone basis. Consequently, we propose here to regard P. nudus as junior synonymy of P. miles .

Porogadus miles generally shows a relatively large morphological diversity, which was also recognized by Machida & Amaoka (1990) and which they considered as reflecting geographical variations of this widespread species. Shcherbachev (1980) described two large specimens (312 and 412 mm SL) from off Western Australia (16°55’S, 114°53’E) as Porogadus sp. 2 , which he considered different from P. miles because of the lower number of (developed) gill rakers (12–13 vs 14–18), the different form of the stomach and the different contour of the supramaxilla. His drawing shows a concave dorsal head profile, which is also not seen in P. miles . These specimens were not reinvestigated in detail for this study (except for a poorly preserved otolith with a high dorsal rim) and could indeed represent a different species. They seem to be similar to the large specimen from off Vanuatu (MNHN 1995-0948), which also has an unusually low gill raker count (11), a much longer extending upper lateral line row with 15–16 pores, a divergent otolith shape with a high dorsal rim and no distinct predorsal lobe, and a narrow sulcus ( Fig. 19J–K ). All three specimens are listed here as P. aff. miles .

Prokofiev (2005) described a large specimen of 364 mm SL from the Emperor Seamounts as Porogadus sp. concluding that it apparently represents an undescribed species. The morphometric measurements of this specimen all fall into the lower end of the variability here observed. Prokofiev considered the main differences to P. miles to be the count of the developed gill rakers (quote: 16 vs 14–15), the presence of a fundal projection of the stomach and the absence of pyloric caeca, 16 precaudal vertebrae (vs quote: 17–18), a wider tooth plate of the vomer and details in the head spines. We consider the number of gill rakers and the width of the vomer to fall well within the variations observed in P. miles while the number of precaudal vertebrae is indeed outside the variability observed by us. His description of the head spines does not give a proper indication of a specific difference. With only a single specimen being recorded by Prokofiev, the number of precaudal vertebrae being the only notable difference, and a specimen from the Necker Ridge (FAKU 47604) not differing significantly from other specimens of P. miles , we regard the specimen from the Emperor Seamounts also to represent P. miles .

We further observed that specimens from the southern Indian Ocean (ZMUC P2397224 and 2397226 from 30°– 32°S and 45°– 46°E; Figs. 19H–I ) and the southern eastern Atlantic (MNHN 2004-1327 from 05°S and 09°E; Figs. 19L–M ) show a relatively more compressed otolith than other specimens (OL:OH = 1.55–1.65 vs 1.75–1.9), but further specimens from the southern Indian Ocean (ZMUC P2397222 at 25°S and 36°E, Figs. 19F–G , and ZM- MGU 14411 from 34°S and 44°E) exhibit the typical, more elongate otolith shape. The observed differences in otolith shape are not supported by other morphological features and therefore are considered to represent intraspecific variability or some specific environmental effect. However, the observed variability of the specimens of P. miles is so large that pertinent diagnostic characters for distinction from other species of the Porogadus miles Group are often rather subtle in nature (see above and below).

Porogadus miles differs from all other species of the Porogadus miles Group except P. longiceps and P. mendax in the higher number of lower lateral line pores until the beginning of the anal fin (23–26 vs 16–21), and except for P. longiceps and P. turgidus in separated ostial and caudal colliculi of the sulcus of the otolith. From P. longiceps it differs additionally in the higher number of long gill rakers (14–18 vs 11–13) and from P. mendax in the presence of scales on the maxilla (vs absent) and 2 postorbital pores (vs 3). From P. turgidus it differs additionally in the lower index OL:TCL of 1.7–2.1 (vs 2.4–2.9).

Figures

FIGURE 1. Schematic drawing depicting occurrences and terminology of head spines and head pore systems in Porogadus (P. miles) in lateral view (upper figure) and dorsal view (lower figure).Abbreviations used for head pore systems are: an = anterior nostril; pn = posterior nostril; io = infraorbital pores; po = postorbital pores; m = mandibular pores; p = preopercular pores.

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 4. Examples of first gill arches. 4A, Porogadus miles ZMUC P2397157, 259 mm SL. 4B, Tenuicephalus multitrabs n. sp. CAS 83066, 156 mm SL. 3C, P. solomonensis ZMUC P771578, 173+ mm SL.

FIGURE 6. Schematic otolith drawings depicting morphological terminology (example from Porogadus miles); upper figure right otolith from inner face, lower figure ventral vie of right otolith. Abbreviations used: OCL = ostial colliculum length, CCL = caudal colliculum length.

FIGURE 17. Porogadus miles Goode & Bean, 1885; 17A,C, ZMUC P77588, 322 mm SL, 37°03’N, 74°07’W, 2150 m; 17B,D, ZMUC P2397222, 274 mm SL, 25°07’S, 36°49’E, 2140–2230 m; 17E–F, MCZ 167870, 39°37’N, 69°31’W, micro-CT scan; 17G, x-ray photograph of USNM 35625, holotype, 145 mm SL, 38°45’N, 73°03’W, 2136 m,; 17H, x-ray photograph of MNHN 86-537, holotype of P. nudus, 198 mm SL, 20°30’N, 16°32’W, 2321 m.

FIGURE 18. Porogadus miles Goode & Bean, 1885, head drawings; 18A–B, MCZ 146877, 257 mm SL, 39°35’N, 70°32’W, 2290–2300 m; 18C–D, MNHN 2004-1327, 282 mm SL, 05°49’S, 09°42’E, 3172–3193 m; 18E, ZMUC P2397222, 274 mm SL, 25°07’S, 36°49’E, 2140–2230 m; 18F, MNHN 86-537, holotype of P. nudus, 198 mm SL, 20°30’N, 16°32’W, 2321 m.

FIGURE 19. Porogadus miles Goode & Bean, 1885, otoliths; 19A–B, BSKU 35715, 38°44’N, 143°11’E, 1950–1960 m, 354 mm SL (A inner face, B ventral view); 19C–D, USNM 316573, 38°45’N, 72°39’W, 2110–2160 m, (C inner face, D ventral view); 19E, ZMUC P77588, 322 mm SL, 37°03’N, 74°07’W, 2150 m, (inner face); 19F–G, ZMUC P2397222, 274 mm SL, 25°07’S, 36°49’E, 2140–2230 m, (F inner face, G ventral view); 19H, ZMUC P2397226, 165 mm SL, 30°30’S, 48°53’E, (inner face); 19I, ZMUC P2397224, 265 mm SL, 32°45’S, 45°31’E, (inner face); 19L–M, MNHN 2004-1327, 282 mm SL, 05°49’S, 09°43’E, 3172–3193 m, (L inner face, M ventral view). 19J–K, Porogadus aff. miles, MNHN 1995-948, 387 mm SL, 14°49’S, 167°15’E, 1360 m, (J inner face, K 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).