This study provides the first comprehensive study of the taxonomy, distribution, and biology of pteropod and heteropod molluscs occurring in the waters surrounding Australia and Papua New Guinea. Approximately 1400 samples were examined from 10 regions encompassing the Northwest Shelf, Gulf of Carpentaria, north and southeast coasts of Papua New Guinea, the Great Barrier Reef and the southeast coast of Australia. Field studies were conducted near Lizard Island, in the northern Great Barrier Reef and Heron Island in the southern Great Barrier Reef from 1985 to 1988. Animals were collected from surface waters and examined live in situ and in vitro. The shelled species are documented with the aid of scanning electron microscopy and photomicrographs and illustrations were made of the shell-less species.
Forty-seven pteropod species/taxa (Thecosomata and Gymnosomata) were found to occur in Australian and Papua New Guinean waters. Thirty-five of these are recorded here for the first time from the region, or their distributional ranges have been considerably extended (> 1000 km) from those previously reported from the literature. First records from the southwest Pacific Ocean are given for the bathypelagic euthecosomes, Clio andreae (Boas, 1886) and C. scheelei (Munthe, 1888). Juveniles of the euthecosome, Hyalocylis striata (Rang, 1828) are described for the first time, this being the only euthecosome whose juveniles were unknown. Two new species of gymnosomatous pteropods, Pneumodermopsis spoeli nov. sp. and Pneumoderma heronensis nov. sp. are described. Thirty-eight pteropod species were found to be cosmopolitan in distribution occurring in both the waters of the southwest Pacific and southeast Indian Oceans. Seven species were only reported from the southwest Pacific Ocean and one species was found exclusively from the southeast Indian Ocean. The highest species diversity of pteropods was reported from the central Great Barrier Reef and southeast coast of Australia.
Twenty-four species of heteropods including veliger stages of the atlantids are documented. Twenty-two species are recorded for the first time from the Australian and Papua New Guinean region or their ranges are considerably extended by more than 1000 km. A trematode digenean parasite is described for the first time from heteropods and the potential role of heteropods as hosts of parasites found in commercially important fish species is discussed. The distribution and biology of the most common Austral ian heteropod, Atlanta gaudichaudi Soule yet, 1852 is investigated in the surface waters offshore from Lizard and Heron Islands. Over 70 % of animals were in veliger stage in both summer and winter months. The abundance of this atlantid was significantly different between sampling regions and abundances were highest in winter months at Lizard Island and summer months at Heron Island.
The sperm ultrastructure of Atlanta gaudichaudi is examined for discussion of the systematics of the heteropods. The phylogenetic position of heteropods is found to conform to that of the Mesogastropoda, especially the Littorinacea by similarity of sperm, presence of nurse cells in the carinariid heteropods and littorinids, and homology of the male reproductive apparatus.
The distribution and seasonal abundance of the holoplanktonic molluscan fauna is examined from the waters of the Great Barrier Reef. Twenty-eight species were collected from surface waters within the Great Barrier Reef and in the waters of the adjacent Coral Sea. Three species, Creseis acicula (Rang, 1828), C. chierchiae (Boas, 1886) and Atlanta gaudichaudi Souleyet, 1852 were found in extremely high abundances, occasionally occurring in blooms. Although the dominant species were similar in both regions, significant differences in the abundance of the most common species were found between Lizard and Heron Islands. These species were generally more abundant in the Trade Wind season at Lizard Island, and in the non-Trade Wind season at Heron Island.