PHYLOGENETIC-RELATIONSHIPS AMONG GIANT DAM SPECIES (MOLLUSCA, TRIDACNIDAE) DETERMINED BY PROTEIN ELECTROPHORESIS

Analyses of allozyme variation at 26 loci in eight species of giant cl ams, collected from the Western Pacific between 1989 and 1991, have co nfirmed the major groupings currently recognised within the family Tri dacnidae on the basis of morphological characters: the two genera Hipp opus and Tridacna, and the subgenera within Tridacna; i.e. Chametrache a (comprising T. squamosa, T. crocea and T. maxima), Tridacna sensu st ricto (containing only T. gigas), and Persikima (comprising T. derasa and T, tevoroa). All these groupings were each supported by several sh ared characters. In contrast to previous views, Persikima was found to be intermediate between Chametrachea and T. gigas. Although statistic al support for branch lengths linking Chametrachea and T. gigas was li mited in maximum-likelihood analyses, the occurrence of several shared alleles between these groups, and none shared between only Chametrach ea and Persikima, suggests a closer relationship between Chametrachea and T. gigas or, at least, an unresolved trichotomy. Morphological dat a traditionally assumed to support a closer association of Chametrache a and Persikima demonstrated that only one shared character linked sub genera, and this character supported an evolutionary association betwe en Chametrachea and T. gigas. These findings, together with the number of shared characters supporting the subgenus Persikima, suggest that Persikima is the most basal offshoot of the Tridacna line, and that th e group may deserve generic status.