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Congrid Leptocephali in Australasian Waters with Descriptions of Conger wilsoni (Bl. and Schn.) and C. verreauxi Kaup.


Included in this group of larvae in the collection are five species, three of which are referred to Ariosoma Swainson, 1838, one provisionally to Alloconger Jordan and Hubbs, 1925, and the last which I cannot recognise as either Chiloconger or Anago (if indeed the latter is distinct from Ariosoma). There is therefore the possibility of a further genus in this subfamily, that this last species may belong to Anago, or that there is a further unknown species of Chiloconger. Leptocephali of the three genera are quite distinct in the distribution of chromatophores, but within Ariosoma with its three species described here only differences in numerical characters serve as specific characters. The same is true of other groups of leptocephali, not only of the Congridae. There are clear divisions in respect of pigment distribution enabling identification usually at the generic level and specific identification rests on numerical characters.

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Ariosoma Swainson, 1838
1838. Ariosoma Swainson, Nat. hist. class. fish. amphib. rept. 1: 220.
1839. Ophisoma Swainson, Nat. hist. class. fish. amphib. rept. 2: 334.
1856a. Congermuraena Kaup, Cat. apod. fish. p. 108.
1870. Congromuraena Günther, Cat. fish. Brit. Mus., 8: 40.
1898. Congrellus Ogilby (partim), Proc. Linn. Soc. N.S.W., 23: 2801.
1925. ?Anago Jordan and Hubbs, Mem. Carneg. Mus., 10 (2): 198.

Although there has been difficulty in establishing conclusively whether Muraena balearica De Laroche, 1809, or Muraena mystax De Laroche, 1809, was the basis for Swainson's Ariosoma, as I have already noted (1963, p. 18) the evidence is that it was A. balearica. Larvae of this species are well known from the central Atlantic and have been adequately described allowing me to recognise that closely similar larvae, differing only in the number of myomeres, occur in the present collection from the Australasian region. On the basis of the similarities, especially in the arrangement of pigment, these leptocephali are referred to Ariosoma.

The Ariosoma larvae fall readily into three clearly-defined groups with 110–119, 134–153, and 157–172 myomeres respectively. Ancona (1928, p. 17) and Gopinath (1949, p. 93), in their examinations of Red Sea and Ceylon leptocephali refer their Ariosoma larvae with about 115 myomeres to Temminck and Schlegel's Conger anago. Ancona confirmed this on the basis of a transitional specimen which had 119 myomeres. As Asano has shown (1962, p. 75) "Conger" anago has 149–159 vertebrae so that both Ancona and Gopinath were in error and their specimens clearly belong with the first group of larvae with 110–119 myomeres listed above from the present collection. Temminck and Schlegel's species, referred at present to Anago Jordan and Hubbs, 1925, is common in the waters of Japan and China, but due to its confusion with the other species discussed here, it has been assigned a much wider geographical range. Although Anago bears a striking resemblance to Ariosoma (Asano, 1962, p. 72) it possesses myorhabdoi or small bones above the epineurals and for this reason it is retained by Asano as distinct from Ariosoma. It is unknown at present whether Ariosoma possesses these structures. The single specimen referable to Ariosoma which I have in hand from Lord Howe Island is in such poor condition that I am unable to check for the presence of myorhabdoi.

Species of Ariosoma occur widely in the Atlantic from the Mediterranean to the Caribbean, in the Indian Ocean from the Red Sea to Natal and Malaya and in the Pacific from Lord Howe Island in the south to the west coast of Central America with the addition of China and Japan should Anago be proved a synonym of this genus. A number of species have been assigned, over the years, to Ariosoma but some of these will undoubtedly be placed finally in species of genera of the Congrinae, the adults of which bear at least a superficial resemblance to Ariosoma. A few of the known valid species have the following vertebral counts: A. balearica with 123–137, from the Central Atlantic and Mediterranean; A. gilberti (Ogilby, 1898) with ca. 116–121, from the Pacific coast of Central America; A. howensis (McCulloch and Waite, 1916) with ca. 153 from Lord Howe Island; A. (=?Anago) Anago with 149–159 from the coasts of Japan and China.