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Introduction
Trawling in moderate depths of 150–350 fathoms by the M. V. Alert during the Chatham Islands 1954 Expedition produced eleven specimens of a small congrid eel not previously recorded from the New Zealand area Subsequent work during 1957 in similar depths in the Bay of Plenty by the Department of Zoology, Victoria University of Wellington and the Dominion Museum and by the Department of Zoology in 600 fathoms in Cook Strait added three more specimens of the same eel Mr. R. Baxter, a commercial fisherman undertaking experimental longlinging for the Department in 1958–59, collected numerous specimens of a remarkably similar, but very much larger eel from traps set in about 430 fathoms near Oaro, Kaikoura. The two species represented by these collections are described in this account.
The congrid eels related to the genus Ariosoma Swainson, 1838, have formed one of the most puzzling and confused groups of the Apodes, a confusion resulting partly from inadequate descriptions by early authors and partly from the relative obscurity of generic characters Parr's detailed but incomplete examination (1927, pp. 1931)of these genera in his attempt to identify a single specimen, was the first step in the resolution of the many problems that had accumulated over the years He concluded that until these genera were more critically examined and their limits more closely defined the only possible course at the time was to extend the genus Ariosoma to a broad sense to include all of these related genera. Since Parr's account, workers in the group have more clearly described their material and added to a more natural classification. The most recent of these was Wade (1946, pp. 181–185)whose key (modified from Reid, 1934, pp. 3–4) sets out the differences between a number of these genera This key forms the general basis for the classification of the two species of Pseudoxenomystax described here, but while it is the most cohesive summary of the genera related to Ariosoma at present available, it is still incomplete.
The New Zealand congrids described in this paper are easily distinguished from members of the genus Conger Oken, 1817, in having the teeth not forming a cutting edge, an upper lip not strongly developed, an otic bulla present and a nasal bone
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present as a small, externally concave element with three finger-like, ventral extensions rather than as a flat, triangular plate. The New Zealand material is further distinguished in having the edge of the upper lip without a free, upturned labial flange, bony projections from the edge of the labial canal present; vomerine teeth in a band, not extending backward on the vomer in a single row, maxillary, premaxillary and vomerine teeth closely united in a single patch at the tip of the upper jaw. These characters immediately set off these New Zealand eels from all genera except Rhynchocymba Jordan and Hubbs, Rhynchoconger Jordan and Hubbs, Pseudoxenomystax Breder, Gnathophis Kaup, Hildebrandia Jordan and Evermann and Bathycongrus Ogilby; Mr. R. H. Kanazawa of the Division of Fishes, U. S. National Museum, informs me that Rhynchocymba is a synonym of Gnathophis The latter genus, type species G. habenata (Richardson, 1848), from Cook Strait, New Zealand, has scroll-like ventrally-directed anterior nostrils and nasal bones consisting of three separate elements on each side, clearly in contrast to the short, simple, anteroventrally-directed tubes and the fused nasal elements of the eels considered here. The remaining genera are all closely similar and not well known but at the present time Kanazawa (personal communication) regards them as falling into three groups which are separated on the size and shape of the vomerine tooth-patch Hildebrandia, having a short, squarish toothed area on the vomer; Pseudoxenomystax, in which the vomerine tooth-patch is long, and Bathycongrus,having a short triangular, toothed area on the vomer; Rhynchoconger, which, with Pseudoxenomystax was held to be a synonym of Rhynchocymba by Wade, can probably be referred to one of the above Bathycongrus, a broad category when it was originally and briefly defined by Ogilby, must now be restricted. Its genotype is Congermuraena nasica, described by Alcock in 1894 as having the vomerine teeth in a single row along the anterior fourth of the bone Kanazawa has examined a specimen of Alcock's species from the Investigator collection and informs me that the vomerine teeth in his specimen are grouped in a short triangular patch with only the most posterior two or three teeth uniserial, that is, somewhat differently than in the type Even recognising variation in this feature in the genus Bathycongrus, on the character of the vomerine tooth-patch the New Zealand eels are therefore referred to Breder's Pseudoxenomystax, type species P. dubius Breder, 1927.
For similar reasons Bassanago Whitley is also referred to Pseudoxenomystax. Whitley describes the vomerine tooth-patch as long, equal to about half the length of the maxillary patch, exactly as in the New Zealand material. The swollen snout, which according to Whitley is so characteristic of the genus Bassanago, is insufficient for it to be considered a distinct genus, especially as this is also a feature of New Zealand specimens of a similar size. In most other characters the type species, B. bulbiceps Whitley, 1948, resembles the eels described below.
No mention has been made up to this point of the presence of the short, fleshy, villiform, epidermal processes over the surface of the body characteristic of adults of both of the New Zealand species, and also known to occur in the eels described under Ariosoma by Smith (1953, p. 393). These structures occur in various forms in Coloconger, Promyllantor and some species of Bathycongrus (personal communication from Kanazawa). So strikingly similar are the New Zealand eels to those described by Smith from South Africa that it is improbable that material from the two areas is to be referred to two different genera. Further information on the South African eels was supplied to the present author by Professor Smith. This shows that these eels can also be placed in Pseudoxenomystax. The upper lip is not developed strongly as an upturned flange; bony projections from the inferior edge of the labial canal are present; the vomerine teeth are distributed in an elongate band, narrowed posteriorly and not extending backward on the vomer in a single row; and the teeth are never pavement-like. Few of the premaxillary teeth are exposed when the mouth is closed, but the number is variable. Smith's
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material, possessing such characters, cannot continue to be identified with Ariosoma and is here referred to Pseudoxenomystax.
Pseudoxenomystax hirsutus n. sp.
Type. V.U.W. Coll.; Dominion Museum No. 2829; 949 mm total length; ovigerous female; 430 fathoms, near Oaro, Kaikoura, New Zealand, November, 1958, by Mr. R. Baxter; commercial cray-fish trap.
Paratypes Four specimens: V.U.W. Coll; Dominion Museum No. 2830; 569 to 1028 mm total lengths; collected with the type specimen.