Systematics, zoogeography and affinity of boring sponges infesting the brown mussel, Perna indica Kuriakose and Nair from the southwest coast of India

A study on the boring sponges infesting the brown mussel population of the southwest coast of India was initiated in 1998, and bored shells collected from five major mussel fishing centres along the coast were analysed on a regular basis. It could be seen that out of 5,600 shells examined during 1998-2000 period, 997 shells were found infested with boring sponges registering an overall incidence of 17.8%, and this, when compared with 3-8 % noticed in natural molluscan beds was too high. The total number of boring sponge species recorded from mussel is nine, and these fall under two families and four genera, the most speciose genus being Cliona with five species. The Enayam centre accounted for all the nine species, and the two new infiltrants, Pione margaritifera and C. lobata formed a common factor with high specific incidence (%) in all the centres surveyed. Out of three conventional species, only two viz. Cliona celata and Pione vasitifca were present in all the centres surveyed with subdued activity and lower incidence %. Pione carpenteri, the third conventional species, could be collected only from Enayam and Kadiyapatnam. Cliothosa hancocki, Thoosa armata and Siphonodictyon minutum were present only at Enayam and were new records to brown mussel. Another species, Alectona wallichii, is also recorded from Enayam. During the present study it could be ascertained that P. vastifica, a conventional boring species of molluscs, has succeeded in colonizing the estuarine realms of Ashtamudi Lake, Kollam due to its euryhaline nature, and hence form a major threat to any molluscan culture farm along this estuary in future. Systematics, description, distribution of all the nine species along with illustrations are given in this paper