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 w ere screened for polymorphism at eleven putative allozyme loci. The sa mples were first identified as belonging to Trochus niloticus L., 1758 , Trochus conus Gmelin, 1791, Trochus maculatus L., 1758 and Tectus py ramis (Born, 1778), but subsequent electrophoretic analysis showed tha t Trochus conus and Tectus pyramis each consisted of at least two repr oductively 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 py ramis to nearly zero in Trochus maculatus. Average Nei's genetic dista nce 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 d istances grouped together all four Trochus species versus the two Tect us species, confirming the validity of these two genera erected origin ally on the basis of shell morphology.