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Zoology Publications from Victoria University of Wellington—Nos. 33 and 34

Gnathophis incognitus n. sp. (Text-fig. 7, A-H)

Gnathophis incognitus n. sp. (Text-fig. 7, A-H).

1936. ? Poutawa habenata (Richardson). Griffin (partim), Trans, roy. Soc. N.Z., 66: 16.

Material Examined. Type specimen: gravid female, 445.0mm total length; Kaikoura coast in 40–50 fathoms; commercial otter trawl; 4/5/61; Dom. Mus. No. 3073. Paratype: male, 350.0mm total length; off Portland Island, Hawke Bay in 30–40 fathoms; commercial otter trawl; 17/5/56; Dom. Mus. No. 1926. Paratype: 237.4mm total length; off Plate Island, Bay of Plenty, in 70–100 fathoms; commercial otter trawl; 16/8/56; Dom. Mus. No. 1983. Paratype: 202.0mm total length; Hawke Bay; Dom. Mus. No. 530. Paratype: 200.5mm total length; Bay of Plenty; Dom. Mus. No. 2612. Three specimens: 70.0mm, 80.1mm and 84.3mm total lengths; Denham Bay, Raoul Island, Kermadec Islands; beach cast; June, 1955; Cant. Mus. Coll. One specimen: 249.0mm total length; Hawke Bay; Cant. Mus. Coll. No. P.137.0. One specimen: 317.0mm total length; Otago, 1893; Otago Mus. Coll. No. A.9.

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Description. Proportional measurements (in per cent total length) and counts from the type and the four paratypes (in parentheses): standard length 98.8 (98.4–98.9), head 15.5 (15.1–16.6), snout 4.4 (4.4–4.7), eye 2.7 (3.1–3.5), interorbital 1.8 (1.9–2.6), cleft of mouth 5.9 (5.8–6.6), postorbital 7.9 (7.8–8.2), branchial aperture 1.8 (1.5–1.8), branchial interspace 4.8 (3.0–3.4), pectoral 4.7 (4.7–6.0), snout-vent 38.4 (37.5–37.9), preanal 41.0 (37.8–39.6), predorsal 16.9 (16.9–17.6), depth just before eye 3.8 (3.1–4.3), depth at pectoral origin 5.6 (4.8–5.3), depth at anal origin 5.5 (4.3–5.2), depth at midpoint of caudal region 3.4 (3.1–3.6). Pectoral rays 13 (12–13), dorsal rays before level of vent 41 40–56), dorsal rays 211 (210–227), anal rays 160 (157–177), caudal rays 5+4 (5 + 4), lateral line pores before level of vent 37 (35–38), vertebrae 145 (139–147).

Body slender, not greatly elongate and little compressed, with prominent myomeres and the vent placed appreciably in front of the midpoint of the body. Head depressed with a sharp bony snout, inferior mouth and large eye. Median fins well-developed but delicate.

Head conical, relatively long, contained about 6.5 times in total length but not clearly differentiated from trunk; snout acutely pointed, bony, about 3.5 in head, projecting in advance of lower jaw by an amount equal to about half diameter of eye, usually a little less; lower jaw rounded in ventral view, slender; mouth conspicuously subterminal, moderately oblique, with cleft extending not beyond a point level with anterior edge of pupil and about three times in head length; upper lip weak, lower thick and fleshy; tongue well-developed.

Teeth generally small but larger on premaxillary-ethmoid than on other dentigerous bones, relatively sharp and conical except on the main part of the vomer, numerous, closely-packed to form broad bands. Maxillary teeth in about four or five longitudinal rows of about 35 teeth, those of the outer row slightly larger than the remainder and the dentigerous area expanding anteriorly with the teeth small and cardiform; a few of the teeth in the medial row molariform. Premaxillary-ethmoid teeth about 12 in number, conspicuous, in an oval patch broader than long, its length contained five times in the length of the vomerine patch; premaxillary-ethmoid teeth almost all exposed in front of the tip of the lower jaw; about a dozen much smaller teeth between this patch and the anterior extremity of the vomerine patch so that the two patches are almost confluent. Vomerine teeth in about three to five longitudinal rows of about 16 teeth each forming a cigar-shaped patch which is about three-fifths as long as the maxillary patch; the teeth large and rounded, short, molariform, more widely spaced than teeth on maxilla or dentary; about a dozen very small, sharp teeth at the anterior extremity of this patch almost in contact with those of the premaxillary-ethmoid patch. Teeth on the dentary similar in number, size and distribution to those on the maxilla although there are fewer minute teeth anteriorly; length of dentigerous area equal to total length of upper area including premaxillary-ethmoid patch, but tip of dentary level with tip of maxilla (not indicated in Text-fig. 7, F).

Anterior nostril small, subterminal, on ventral surface of snout level with anterior extremity of premaxillary-ethmoid patch of teeth; a short external tube with a small free flap so that the rim is not simple. Posterior nostril small, placed a little in advance of eye on a level slightly above the horizontal diameter; usually slit-like with a raised complete rim but no external tube. Eye circular to slightly oval, large, about three in postorbital; fleshy interorbital space narrow but difficult to determine accurately, usually considerably less than eye. Branchial aperture lateral with a concave free edge, slightly oblique, with the ventral extremity more posterior and with the dorsal extremity a little below middle of pectoral base, page 39
Text-fig. 7.—Gnathophis incognitus n. sp., type, 445.0mm total length, female, Dom. Mus. No. 3073, Kaikoura, 4/5/61. Fig. A—Lateral view, arrows indicate origin of dorsal, anterior margin of vent and origin of anal. Fig. B—Dorsal view. rig. C Lateral view of head to indicate minute sensory papillae and prominent myomeres. Fig. D—Dorsal view of head. Fig. E—Ventral view of snout to show anterior nostrils, pores and premaxillary-ethmoid teeth. Fig. F—Pattern of upper (left) and lower (right) teeth. ig. G—Left preorbital bones, lateral view. Fig. H—Caudal skeleton (200.5mm t.1, Dom. Mus. No. 2612).

Text-fig. 7.—Gnathophis incognitus n. sp., type, 445.0mm total length, female, Dom. Mus. No. 3073, Kaikoura, 4/5/61. Fig. A—Lateral view, arrows indicate origin of dorsal, anterior margin of vent and origin of anal. Fig. B—Dorsal view. rig. C Lateral view of head to indicate minute sensory papillae and prominent myomeres. Fig. D—Dorsal view of head. Fig. E—Ventral view of snout to show anterior nostrils, pores and premaxillary-ethmoid teeth. Fig. F—Pattern of upper (left) and lower (right) teeth. ig. G—Left preorbital bones, lateral view. Fig. H—Caudal skeleton (200.5mm t.1, Dom. Mus. No. 2612).

page 40 Vent protruding into the lateral profile, in the type specimen enlarged due to the gravid condition.

Median fins delicate in life, rather fleshy on preservation, their posterior tips confluent with the caudal; rays clearly visible. Dorsal fin well-developed, its maximum height near level of vent, when fully extended contained about three times in body depth at level of vent; originating only slightly in advance of level of midpoint of pectoral fin; rays rather few compared with most other congrid eels. Anal fin a little less strongly developed than the dorsal, its maximum height on full extension about halfway along caudal region and about 3.5 in depth of body at vent. Caudal fin rounded and the rays relatively short, giving an impression that the tail is used for burrowing. Pectoral fin elongate-oval in shape, slender, originating slightly above mid-lateral level and directed somewhat posterodorsally, its length a little greater than snout.

Text-fig. 8.—Frequency of myomeres in (a) Gnathophis habenatus and (b) G. incognitus.

Text-fig. 8.—Frequency of myomeres in (a) Gnathophis habenatus and (b) G. incognitus.

Lateral line very conspicuous as a raised ridge, arising high up on head and reaching midlateral level just posterior to vent. Pores simple, not carried on the ends of short tubes, clearly visible except along the most posterior part of the caudal region. Cephalic sensory pores restricted to one occipital pore, five or six circumorbital pores, two opercular pores and a series along ventral aspect of lower jaw. Two small pores lie immediately in front of, and medial to, the anterior nostril on the ventral surface of the snout. An inconspicuous but long slit occurs dorsally on each side of snout tip. Several series of surface sensory organs, indicated by minute papillae, occur on the head and in a longitudinal row above the lateral line although the papillae of the latter series are sparse and widely spaced. The cephalic papillae are distributed in lines on the dorsal surface of the snout, behind eye, on lower jaw and in semicircular rows on operculum and in front of pectoral fin.

Colour in life olive-green over silver, with a silver iris; in preservative it is dark brown on dorsal aspect of head and above lateral line, lighter below, with the whole of the dorsal and the posterior part of the anal edged with a narrow black band.

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Remarks. Gnathophis incognitus differs from G. habenatus in having 139–147 vertebrae, a small free flap on the anterior nostril (Text-fig. 7, E), premaxillary-ethmoid teeth in an oval patch of teeth which extends noticeably in front of the maxillary patches, numerous sensory papillae and pores on the head and body, a pointed pectoral fin, a lateral line which is rather more conspicuous as a raised ridge and a slightly longer caudal fin; the present species has only sparse molariform teeth on the medial aspects of the maxilla and dentary but more numerous minute, pointed teeth on the anterior parts of these bones than does G. habenatus. It is a more slender eel with a relatively short preanal region, usually less than 40% of the total length, and is duller in colouration. G. incognitus inhabits waters of about 30 fathoms to the edge of the continental shelf and appears to have a more northerly distribution in New Zealand than does G. habenatus habenatus.

G. incognitus resembles G. xenicus (Matsubara & Ochiai, 1951) of the Japanese region in being slender and long in the tail, but the latter has 152–154 vertebrae and more pores before the level of the vent.