GENETIC-RELATIONSHIPS AMONG THE TOPSHELLS TROCHUS AND TECTUS (PROSOBRANCHIA, TROCHIDAE) FROM THE GREAT-BARRIER-REEF

Large species of Trochus and Tectus common on the Great Barrier Reef were screened for polymorphism at eleven putative allozyme loci. The samples were first identified as belonging to Trochus niloticus L., 1758, Trochus conus Gmelin, 1791, Trochus maculatus L., 1758 and Tectus pyramis (Born, 1778), but subsequent electrophoretic analysis showed that Trochus conus and Tectus pyramis each consisted of at least two reproductively isolated, sympatric species. Some of these species matched older descriptions, based on shell morphology, of taxa which had since been synonymised. Allozyme polymorphism ranged from high in Tectus pyramis to nearly zero in Trochus maculatus. Average Nei's genetic distance between Trochus species was 1.726. Genetic distance between Tectus species was 1.510. Nei's genetic distances between Trochus and Tectus ranged from 3.226 to infinity. A phylogenetic tree based on genetic distances grouped together all four Trochus species versus the two Tectus species, confirming the validity of these two genera erected originally on the basis of shell morphology.