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New Zealand Coelenterates Ctenophores from Cook Strait

Discussion

Discussion

The very broad paragastric canals distinguish P. helicoides from all known species of Pleurobrachia. They can further be distinguished by body shape, pigmentation, etc. Firstly they are distinguished from P. pileus O. F. Muller 1776 by their cylindrical body shape, long comb rows and by their colour—pale pink underneath the comb rows and orange-pink tentilla; from P. bachei A. Agassiz 1865 and P. globosa Moser 1909 by the difference in position of the junction of the adradial canals with the meridional canals; from P. pigmentata and P. striata Moser 1909 by the absence of pigmented "paddle plates" and from P. crinata Moser 1909 and P. australis (Benham) 1907 (Syn. Euplokamis australis Benham 1907) by the absence of a funnel-shaped collar round the mouth. The general body shape, comb rows, and canal system of P. helicoides is similar to P. australis and both species have been taken from Cook Strait, but not at the same time. The weight of evidence is such that despite the general similarity in appearance and canal structure P. helicoides does not fall within the specific description of P. australis as given by Benham. The broad paragastric canals, tightly coiled tentilla, the presence of colour, and the lack of a funnel-shaped collar round the mouth distinguish P. helicoides from P. australis. Nevertheless it must be borne in mind that only a few specimens of each species have been examined and it would not be surprising to find in a genus where wide variation in form, colour, and even canal structure is permissible within a species that examination of a large number of specimens would yield sufficient evidence for the specific description of P. australis to be widened to include those forms at present distinguished as P, helicoides. P. helicoides may be in fact only a seasonal variant.