Neobythitinae Radcliffe, 1913

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 : 23-25

Subfamily Neobythitinae Radcliffe, 1913

Genus Porogadus Goode & Bean, 1885

Porogadus Goode & Bean, 1885: 602 , type species by monotypy Porogadus miles Goode & Bean, 1885 .

Dermatorus Alcock, 1890: 298 , type species by monotypy Dermatorus trichiurus Alcock, 1890 .

Celema Goode & Bean, 1896: 329 , type species by subsequent designation Porogadus nudus Vaillant, 1888 .

Moebia Goode & Bean, 1896: 331, type species by monotypy Bathynectes gracilis Günther, 1878 .

Porogadus: Cohen & Nielsen, 1978 ; Nielsen, Cohen, Markle & Robins, 1999.

Diagnosis (adopted and altered from Nielsen et al., 1999). A genus of the subfamily Neobythitinae characterized by the following combination of characters: Body long and slender; depth at anus more than 10 times in standard length, prominent mucous cavities and large pores along the infraorbital and mandibular-preopercular canal systems; spines on head variably developed but at least containing ethmoidal spine; upper jaw ends well behind eye; 1 median basibranchial tooth patch, rarely 1 pair of small lateral basibranchial tooth patches in addition; lateral line represented by 3 rows of circular organs variously developed from one species to another and by a row of easily shed modified scales; developed gill rakers 11 to 21; pectoral-fin rays 15 to 23; precaudal vertebrae 16 to 19; ratio HL:HD 1.5 to 2.1; vomer with 1 to 7 rows small villiform teeth (except P. guentheri with only few teeth); palatine with 2 to more than 6 rows small villiform teeth.

Similarity. Porogadus shares with Alcockia Goode & Bean, 1896 , Bathyonus Goode & Bean, 1885 , Penopus Goode & Bean, 1896 and Tenuicephalus n. gen. described in the following the slender body and mucous cavities on the head. These genera were considered to be interrelated by Cohen & Nielsen (1978) with whom we agree. Alcockia further shares with Porogadus the presence of sharp spines on the head, but differs in the presence of 2 median basibranchial tooth patches (vs 1, occasionally flanked by a small pair of tooth patches), 7 developed rakers on the first gill arch (vs 11 to 21), and the upper jaw terminating beyond eye (vs well behind eye). Alcockia is further characterized by a doubled infraorbital canal system below the eye, underlain by a bony ridge towards the upper jaw, a much widened and serrated preopercle and specialized scales on certain positions of the head ( Fig. 2 ). Bathyonus differs from Porogadus in the large head (HL about ½ preanal length and c. 20% of SL vs 14–18.5% of SL), absence of prominent spines on head and lower rays of pectoral fin free. Bathyonus is further characterized by a broad head with numerous small sensory papillae along the mandible and three small papillae on the opercle ( Fig. 2 ). Penopus shares with Porogadus also the lateral line system and the upper jaw terminating far beyond the eye but differs in the anteriorly very depressed head with the snout long and projecting over mouth, the absence of head spines except for a strong opercular spine and 4 to 5 spines at the lower angle of the preopercle, the very small non-imbricate scales on the head ( Fig. 2 ) and the 8 to 10 developed gill rakers on the first gill arch (vs 11 to 21). For differentiation from the new genus Tenuicephalus see below.

Species. We consider 10 of the previously described 15 species as valid for Porogadus and describe 6 new species in the following: Porogadus abyssalis Nybelin, 1957 from the deep Atlantic Ocean, P. atripectus Garman, 1899 from the East Pacific, P. caboverdensis n. sp. from the East Atlantic, P. catena ( Goode & Bean, 1885) from the Atlantic, P. dracocephalus n. sp. from the Indo-West Pacific, P. gracilis ( Günther, 1878) from the Indo-West Pacific, P. guentheri Jordan & Fowler, 1902 from the North-West Pacific off Japan, P. lacrimatus n. sp. from the West Pacific, P. longiceps Garman, 1899 from the East Pacific, P. melanocephalus Alcock, 1891 from the Indian Ocean, chiefly the Gulf of Bengal, P. mendax n. sp. from the East Atlantic, P. miles Goode & Bean, 1885 worldwide under tropical to temperate seas except the East Pacific, P. promelas Gilbert, 1892 from the East Pacific, P. solomonensis n. sp. from the West Pacific, P. trichiurus ( Alcock, 1890) from the Indo-West Pacific and P. turgidus n. sp. from the East Atlantic.

Species Groups. The head proportion in combination with shape of the snout and the presence and intensity of spines on the head represent the best means to visually identify species groups. We recognize 4 species groups within Porogadus , but follow Nybelin (1957) in not assigning formal subgeneric ranking to them at this stage. Even though nominal generic names are available for three of the four species groups, we believe that a more extensive phylogenetic analysis is required before further taxonomic division can be justified. The four species groups are as follows.

1. Porogadus miles Group. The species of the Porogadus miles group are characterized by the combination of a long head with a slender snout and abundant and strong head armature. It comprises the largest group and includes P. atripectus , P. caboverdensis n. sp., P. dracocephalus n. sp., P. longiceps , P. mendax n. sp. P. miles and P. turgidus n. sp. However, the two species P. atripectus and P. turgidus n. sp. are intermediate in many characters with the following group in respect to the head proportions but have the slender snout of the Porogadus miles Group.

2. Porogadus trichiurus Group. Specimens of the Porogadus trichiurus group have a short head with intense head armature and a broad snout. It comprises the second largest group with four species: P. guentheri , P. lacrimatus n. sp., P. solomonensis n. sp. and P. trichiurus .

3. Porogadus gracilis Group. This species group is characterized by a slender head and snout with weak spines and comprises the species P. abyssalis , P. gracilis and P. melanocephalus .

4. Porogadus catena Group. This group contains only two species with a short head and snout and weak spines: P. catena and P. promelas .

Key to the species of Porogadus

(see also tables 1 to 7)

1 Well developed spines on different positions of the head...................................................... 2

- No or weak spines on the head except for ethmoidal and occasionally infraorbital spines............................ 13

2 HL:HD = 1.81–2.08................................................................................... 3

- HL:HD = 1.52–1.80 (rarely 1.82)......................................................................... 9

3 Lower lateral line pores until beginning of anal fin 22–26..................................................... 4

- Lower lateral line pores until beginning of anal fin 16–21..................................................... 7

4 Long gill rakers ≤13................................................................................... 5

- Long gill rakers ≥14................................................................................... 6

5 Predorsal>19% of SL; small opercular flap; sulcus of otolith with divided colliculi................ Porogadus longiceps

- Predorsal 17–18% of SL; large opercular flap with radial ridges; sulcus of otolith with undivided colliculi............................................................................................... Porogadus mendax n. sp.

6 Maxilla with scales on rear portion; sulcus of otolith with divided colliculi; otolith length to total colliculi length <2.0............................................................................................ Porogadus miles

- Maxilla without scales; sulcus of otolith with undivided colliculum; otolith length to total colliculum length>2.1......................................................................................... Porogadus mendax n. sp.

7 Vomer narrow, with 1–3 rarely 4 rows of teeth; sulcus of otolith with undivided colliculum........................... 8

- Vomer wide, with 4–5 rows of teeth; sulcus of otolith with divided colliculum................ Porogadus turgidus n. sp.

8 Palatines narrow, with 2–5 rows of teeth; maxilla with no or single line of scales along upper rim; otolith length to total colliculi length <2.0................................................................. Porogadus dracocephalus n. sp.

- Palatines wide, with 4–9 rows of teeth; maxilla with scales on rear portion; otolith length to total colliculi length>2.1................................................................................ Porogadus caboverdensis n. sp.

9 Vomer naked or with few teeth or 1–2 rows of teeth; opercular spine sharp, free................................... 10

- Vomer with 2–5 rows of teeth (rarely 1 row in P. trichiurus ); opercular spine flap like.............................. 11

10 HL:HD = 1.52–1.60; predorsal = 15.4–16.3; gill rakers not bladed....................... Porogadus lacrimatus n. sp.

- HL:HD = 1.71–1.80; predorsal = 13.7–14.7; gill rakers bladed................................ Porogadus guentheri

11 Developed gill rakers 18–21, with no or very few intermittent plates; palatines with 2–4 rows of teeth; OL:OH = 1.1–1.3..................................................................................... Porogadus trichiurus

- Developed gill rakers 15–17 (rarely 18), with many and regularly occurring plates in between; palatines with 5 or more rows of teeth; OL:OH = 1.5–1.7............................................................................... 12

12 Spines along inner rim of preopercle; small scales around eye; median basibranchial without lateral pair (single rarely present)............................................................................ Porogadus atripectus

- No spines along inner rim of preopercle; no scales around eye; median basibranchial and paired basibranchial....................................................................................... Porogadus solomonensis n. sp.

13 HL:HD = 1.73 (rarely 1.70)–2.09, with long slender snout.................................................... 14

- HL:HD = 1.50–1.70 (rarely 1.73), with short, stubby snout................................................... 16

14 Precaudal vertebrae 19; pectoral fin rays 20–23............................................. Porogadus abyssalis

- Precaudal vertebrae 16–18; pectoral fin rays 15–19......................................................... 15

15 Head black; palatine with 5–7 rows of teeth; otolith length to total colliculum length = 3.3..... Porogadus melanocephalus

- Head brown like body; palatine with 3–5 rows of teeth; otolith length to total colliculum length = 2.5..... Porogadus gracilis

16 Supratemporal and postemporal spines weak; scales on cheeks and opercle equally large; OH:OT = 1.1–1.2; dorsal rim of otolith regularly rounded.................................................................... Porogadus catena

- No supratemporal and postemporal spines; scales on cheeks larger than scales on opercle OH:OT = 1.25–1.5; dorsal rim of otolith anteriorly expanded.............................................................. Porogadus promelas

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).