High level of genetic divergence between sympatric color morphs of the littoral sea anemone Anthopleura orientalis (Anthozoa : Actiniaria)

Using enzyme electrophoresis and nematocyst analysis, the sympatrically occ urring "light" and "dark" color morphs of the sea anemone Anthopleura orien talis from the Sea of Japan were shown to be two valid species. The "light" morph was identified as A. orientalis (Averintsev, 1967 Issledovaniya faun y morel. Vyp. 5 (13). Nanka, Leningrad, pp. 62-77). while the "dark" morph was designated as Anthopleura sp. The analysis of 21 isozyme loci revealed high value of Nei's genetic distance (D = 1.284) between the two species, w hich are indistinguishable in their external morphology. The mean values of observed and expected heterozygosities for A. orientalis and Anthopleura s p. are high (H-o=0.252 +/- 0.061, H-e = 0.250 +/- 0.061 and H-o = 0.327 +/- 0.052, H-e = 0.351 +/- 0.054, respectively). The species differ significan tly in the size of spirocysts and nematocysts, among which the atrichs from acrorhagi and the basitrichs from actinopharynx contribute most to the obs erved difference.. Strong qualitative difference is revealed between distri butions of nematocysts in mesenteric filaments of the two sea anemone speci es studied. The possible conspecificity of Anthopleura sp. with Anthopleura artemisia (Dana, 1848) is discussed and the conclusion made that these an two separate species. (C) 2000 Elsevier Science Ltd. All rights reserved.