Clypeomorus petrosa (W. Wood 1828)

Clypeomorus petrosa (Wood)

Although Clypeomorus petrosa has a wide Indo-Pacific distribution, close examination of numerous samples from throughout its range reveals three allopatric geographical varieties. Populations from continental regions in the Indian Ocean are quite distinct from those in the western South Pacific while those from the Ryukyus, and the Philippine and Indonesian Archipelagos are morphologically different from those indicated above. The Indian Ocean morphs were considered to be varieties of Clypeomorus petrosa and given the varietal name gennesi Fischer and Vignal in P.H. Fischer, 1901; those from the Philippines were recognized as a separate taxon and named Cerithium chemnitzianum by Pilsbry (1901).

I initially considered each of the three groups as a separate species, but in areas of parapatry there are intergrades that indicate the petrosa complex is best regarded as a superspecies, sensu Mayr (1969:52–53). According to this concept, the component species of a superspecies are designated ignated as semispecies, a term used to include borderline cases of speciation. The morphologies of these three taxa were compared with each other and the discriminating characters for each taxon are presented in each respective subspecific discussion. Statistical analyses of shell length, shell width, aperture length and aperture width were also made among the three taxa. A one way Analysis of Varience (ANOVA) shows all F values are highly significant. Paired comparisons were made using Student-Neuman-Keuls Post Hoc Comparison. The results are presented in Table 16. All comparisons are significant except for shell length and shell width between Clypeomorus petrosa petrosa and C. petrosa chemnitziana. Clypeomorus petrosa gennesi differs significantly from these two taxa in all characters and may be sufficiently distinct to warrant specific recognition. I have not seen C. p. gennesi alive and do not know its anatomy well. There is a lack of sufficient comparative material from the western Indian Ocean and the presence of intergrades in areas of parapatry is uncertain. For practical purposes I shall follow Mayr's (1969:197) advice and treat these allopatric populations of doubtful rank as subspecies. It is obvious that more careful work is needed on the petrosa complex by local workers. For the present, I feel justified in regarding these taxa as subspecies and alert future workers about the possible problems to be investigated in this group.