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

L. Anguilla megastoma (Text-fig. 1, A, B, C)

L. Anguilla megastoma (Text-fig. 1, A, B, C)

Material Examined. Two specimens, 23.7mm and 26.4mm total lengths; Institut Français d'Océanie Station 56–4–3; 12° 55′ S., 170° 04′ E.; 27/9/56 (2324 hours); horizontal tow in 70m; 0.5m net, No. 2 mesh.

Description. Measurements in mm: total length 26.4 (23.7), head 2.7 (2.7), snout 0.9 (0.9), eye 0.5 (0.6), upper jaw 1.0 (1.0), postorbital 1.3 (1.2), pectoral 0.9 (0.8), preanal 18.8 (17.4), predorsal 16.8 (16.2), depth just before eye 1.2 (1.0), depth at pectoral origin 2.2 (3.1), depth at midpoint between pectoral and vent 4.6 (4.2), depth at anal origin 4.4 (3.2). Branchiostegal and pectoral rays not obvious, dorsal and anal elements visible only near tip of caudal region, caudal rays 2 + 2 + 2 + 2 + 1. Teeth 1 + 1 + III + 3 over 1 + III + 2. Myomeres 72 + 39 = 111 (114). a–d = 7 (7). 1st vertical blood-vessel at 17th myomere, 2nd at 42nd and 3rd at 48th. Anterior margin of gall-bladder at level of 29th myomere.

Body elongate but not excessively so, much compressed, not very deep and tapering a little more gradually in front of midpoint of body. Head short, about one-ninth of total length, its lower profile indented at the throat to make the head region clearly differentiated from the trunk; snout short, equal to one-third of head length, acutely pointed with its dorsal profile conspicuously concave and anterior and posterior nares almost separated; eye moderate, oval, with its greatest diameter vertical and a little less than length of snout; gape oblique, extending to level of anterior margin of eye; teeth relatively large, very acute, eight in the upper jaw, projecting outside the six of the lower jaw and distributed as follows: a large, forwardly-projecting grasping tooth is preceded by a tiny, needle-like tooth placed almost on the dorsal surface of the snout and is followed by three large teeth which become progressively smaller; this series is followed by three noticeably smaller teeth, the most posterior of which is placed almost directly under the anterior rim of the orbit; the teeth of the lower jaw are similar in page 6 size and grouping to those of the upper with the most posterior tooth placed a little in advance of the level of the last upper tooth. Pectoral fin relatively large, equal to length of snout and elongate-oval in shape; base of fin thick and fleshy, web of fin thin, supported by delicate fin-rays which are poorly developed. Dorsal fin low, with only the radials visible at the end of the caudal region. Anal fin similar. Caudal fin conspicuously separated from the tips of the dorsal and anal fins.

Colour in preservative translucent, with black pigment confined to the chorioid of the eye.

Remarks. The two specimens described here belong unquestionably to the genus Anguilla. They agree very well with Group I (Anguillidae) of Ancona (1928, p. 102) in which the body is relatively short, high, in the form of an olive leaf, the intestine is straight and not festooned or swollen; the vent is about two-thirds of the length along the body; the dorsal fin originates a little in advance of the level of the vent; there is no pigmentation in the body except in very small specimens (5.0mm to 10.0mm). Both are long-finned larvae having seven myomeres between the dorsal and anal origins. They have a relatively high number of myomeres for Anguilla larvae, 111 and 114, suggesting that they are the young of either A. dieffenbachi (109–116 vertebrae) or A. megastoma (108–116 vertebrae). They were both collected at the same station, north-east of the New Hebrides, which is well outside the known distribution of A. dieffenbachi (a species restricted to New Zealand). Although the position of capture does not entirely rule out the possibility that they are the young of the latter species, since its breeding area is possibly as far north as New Caledonia, I am satisfied mainly for geographical reasons that the two larvae are the young of the other long-finned species with a high number of vertebrae—i.e., A. megastoma.

The two specimens of A. megastoma described above are evidently about half-grown, possessing only a few teeth (8–9) compared with the average full complement of about 18–20 in Anguilla larvae about to undergo metamorphosis. In both specimens the olfactory organ is not well developed, but in the larger the anterior and posterior nares are near to separation; the vertebral column is well chondrified; the vent is not greatly posterior; the heart is well developed, and the cranium well ossified.