Parasaccogaster rhamphidognatha ( Cohen, 1987 )

Nielsen, Jørgen G., Schwarzhans, Werner & Cohen, Daniel M., 2012, Revision of Hastatobythites and Saccogaster (Teleostei, Bythitidae) with three new species and a new genus, Zootaxa 3579, pp. 1-36 : 32-33

Parasaccogaster rhamphidognatha ( Cohen, 1987)

Figs. 23 , 24 , 26 , Tables 1 , 2, 7

Saccogaster rhamphidognatha Cohen 1987: 1 , fig. 1 (type locality: Gulf of Mexico). Saccogaster rhamphidognatha: Nielsen et al. 1999: 109 .

Material examined (1 specimen, 60 mm SL). Holotype: LACM 44189-1, male, 60 mm SL, Gulf of Mexico, Mississippi delta, 29°13.5’N, 88°16.5’W, R/V Alaminos, st. 69A 13-43, 210 m, 4–16 Oct. 1969.

Diagnosis. Parasaccogaster rhamphidognatha differs from the other two species of the genus by the antrorse, hook-like projection at the postero-ventral angle of the maxillary, a median spine on frontals above and behind eyes and the low number of pectoral fin rays (12). Also the following combination of characters is diagnostic: A strong, ethmoidal spine; pectoral peduncle prolonged and adnate to body; 2–3 slightly developed rakers on anterior gill arch; palatines with a single tooth row; gill filaments on anterior arch short, 1–2 times length of developed rakers; precaudal vertebrae 20 and total vertebrae 58; fin rays in dorsal 77, anal 49 and pectoral 12.

Similarity. Parasaccogaster rhamphidognatha is most similar to P. n o r m a e with hidden opercular spine, nasal chamber not sooty black and distinctly more anal fin rays and vertebrae than found in P. melanomycter . P. rhamphidognatha differs from P. normae by the shorter gill filaments on anterior arch (1–2 times length of long rakers vs. 4–5 times), fewer pectoral fin rays (12 vs.17–19), presence of ethmoidal spine (vs. spine absent) and a single median spine on frontal (vs. pair of small spines).

Description. The principal meristic and morphometric characters are shown in Table 7 . Head and body elongate and compressed with blunt snout and tapering tail. Scales absent. Lateral line obsolete. Dorsal fin origin above gill slit, anal fin origin well behind midpoint of fish and pectoral fins very short ending 1/5 to origin of anal fin. Anterior gill arch with 2–3 flat, spiny plates on upper branch, a short, slightly prolonged raker in angle and lower branch with 1–2 similar sized rakers followed by six spiny plates. Gill filaments short. Two pseudobranchial filaments. The intromittent organ is provided with a 6 mm long penis indicating a ripe male.

Axial skeleton (from radiographs): Number of precaudal vertebrae 20. Anterior neural spine one third the length of second spine. Neural spines gradually decreasing in length. Neural spines 6–8 with slightly blunt tips. Tips of all other neural and haemal spines pointed. Parapophyses on vertebrae 4–20. Ribs obsolete.

Dentition: Palatines with small, pointed teeth in a single row. Vomer boomerang-shaped with band of small, pointed teeth. Premaxillaries and vomer with an outer, narrow band of granular teeth and an inner row with larger, needle-like teeth.

Head morphology: Head profile not concave above eyes. Head with single, strong, median, subdermal spine on frontal plate above and behind eyes, a strong median, subdermal, ethmoidal spine in front of eyes and a broad, blunt, sub-dermal spine above each eye. Anterior nostril placed close to upper lip, posterior nostril about three times as large, lunate-shaped, placed at half way distance to small eye. Head pores: 1 supraorbital pore at tip of snout, 2 anterior infraorbital pores below and in front of eye, 1 anterior mandibular pore at tip of jaw. Head skin thick, loose. Head with blunt snout, sunk-in eye covered by window of translucent skin. Upper jaw ends well behind eye with posterior margin strongly vertically expanded, somewhat hook-shaped. Flat opercular spine hidden below thick skin. No subdermal preopercular spine. Gill opening ending at about level of dorsal margin of pectoral peduncle.

Otoliths: Not extracted from unique holotype.

Coloration: Head and body pale. Vertical fins brownish distally.

Biology and distribution ( Fig. 26 ). Parasaccogaster rhamphidognatha is only known from the holotype caught at a depth of 210 m in the Gulf of Mexico.

Figures

FIGURE 23. Parasaccogaster rhamphidognatha, holotype, LACM 44189 - 1, SL 60 mm (photo R. Feeney).

FIGURE 24. Parasaccogaster rhamphidognatha, holotype: A—Lateral view of head. B—Lateral radiograph of head (photo R. Feeney). C—Dorsal view of head. D—Anterior right gill arch.

FIGURE 26. Geographic distribution of Parasaccogaster and Saccogaster in East Pacific and West Atlantic waters. Each marking may represent more than one locality.