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The eel genus Benthenchelys (Fam. Ophichthidae) in the Indo-Pacific
Castle, P.H.J. (1972). The eel genus Benthenchelys (Fam. Ophichthidae) in the Indo-Pacific. The Carlsberg Foundation's oceanographical expedition round the World 1928-30 and previous Dana-expeditions. Dana-Report, 82. Andr. Fred. Høst & Søn: Copenhagen. 30 pp.
Part of: The Carlsberg Foundation's oceanographical expedition round the World 1928-30 and previous Dana-expeditions. Dana-Report. C.A. Reitzels Forlag/Oxford University Press: Copenhagen. ISSN 0070-2668, more

Available in Author 
    VLIZ: Expedition Reports [255293]

Keywords
    Expedition reports; Ophichthidae Günther, 1870 [WoRMS]; Marine
Author keywords
    Benthenchelys

Author  Top 
  • Castle, P.H.J.

Abstract
    1) Benthenchelys Fowler, 1934, a genus of Indo-Pacific eels formerly referred by various authors to the family Derichthyidae and Congridae is recognised to belong to the Ophichthidae. (2) It has well developed jugostegalia (that is, numerous detached 'branchiostegal rays' supporting the throat and overlapping in the ventral midline), no free tongue, a transverse sensory canal and median pore in the fused frontal bones, and reduced basibranchials, pterygoid arch and pectoral girdle. (3) The hyomandibula is inclined obliquely forwards and there are short but strong neural spines. In these ways Benthenchelys differs from all other ophichthids and indicates that it is at least as unspecialised as Echelus itself (Ophichthidae, Echelianae). (4) Osterological characters show that Benthenchelys resembles the Congridae, more particularly the subfamily the Congridae, more particularly the subfamily Heterocongrinae (garden eels), and is less specialised even than Gorgasia. (5) Although formally referred here to the Ophichthidae (subfamily Echelianae), Benthenchelys must be regarded as a structural intermediate between the echeline ophichthids and the heterocongrine congrids. It is suggested that the Heterocongrinae, Benthenchelys and the Echelinae evolved from a stock which probably included eels similar to the subfamily Bathymyrianae of the Congridae. (6) Some 290 specimens referable to Benthenchelys were studied. Except for 2 collected by the 'Orsom III' near new Caledonia, all were taken by the 'Dana' Expedition Round the World 1928-30 in the Indo-Pacific. There are no major observable differences in characters of individuals throughout this series to indicate more than a single species B. Cartieri Fowler, 1934, type locality Sulu Sea. However, slight differences in numbers of vertebrae and fin-rays of specimens from the central Pacific, Sulu sea and northern indian ocean merit the recognition of 3 subspecies: B.cartieri pacificus new subspecies, B.c. Cartieri Fowler, 1934, and B.c.indicus new subspecies, respectively. (7) The above differences which indicate subspecific distinctions of samples from the 3 areas may be resultant from variations in the physical conditions during embryonic development, but no information on the latter is available for this to be investigated further at the present time. (8) Individuals of B. Cartieri reach full maturity at much less than 140 mm total lenth; mature female are slightly larger than mature males; the ovary contains similar to 700 ova, each of which attains at least 0.9 mm diameter. (9) Benthenchelys is only to be found in the central Indo-Pacific in the open ocean, in similar to 200 m over depths of 4000 m and in water of moderate temperature (13 degree C- 23 degree C). (10) The life span of individuals of the 3 subspecies is apparently relatively short, possibly less than a year. Larvae are at present unknown or unrecognized as such amongst known leptocephali. Gonads develop at 65 mm total length and spawing is possibly a more or less continuous process throughout the year. (11) The implications of such a short life span are either a) that Benthenchelys maintains the brief, pelagic, primitive way of life of its presursors, similar to that of the remainder of the Elopomorpha, or b) that its life cycle is specialised, the adult benthic phase having been eliminated by the attainment of sexual maturity at an early age, indicating at least incipient neoteny.

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