Life history of Perarella schneideri (Hydrozoa, Cytaedidae) in the Ligurian Sea

Abstract

Perarella schneideri is a cytaeidid hydroid living in association with the bryozoan Schizoporella longirostris. In this study we have distinguished the presence of two kinds of polyps in its colonies: large gastrozooids and very extensible filiform polyps with 4 short tentacles. A study of the relationships between the hydroid and its host indicates a parasitic behaviour of P. schneideri on bryozoan adult colonies, and predation on bryozoan larvae. Study of hydroid stomach contents indicates that the trophic strategy of P. schneideri depends on two food sources: (i) a benthic one, mainly constituted of nematodes and polychaetes and (ii) a bryozoan source, which is performed in various ways. The Perarella schneideri colonies are, in turn, a food source for halacarids which perforate the hydranth wall and, penetrating the gastrovascular cavity, suck the semi-digested prey without evident damage to the polyps.

Keywords

• hydrozoa
• cytaeididae
• life cycle
• trofic strategy
• parasitism
• commensalism
• bryozoa