Das kommensalische verhältnis zwischen Periclimenes imperator (Decapoda: Palaemonidae) und Hexabranchus sanguineus (Nudibranchia: Doridacea)

The Red Sea nudibranch Hexabranchus sanguineus, rare in this region, was found in the Gulf of Aqaba together with a pair of commensal shrimp, Periclimenes imperator. The behaviour of the shrimp, especially as regards their adaptation to the host, was studied in the field and in an aquarium. The shrimp live on the sea slug, feeding on particles adhering to its mucous surface; they move on it even when it is swimming. The shrimp's colour is well adapted to that of the host. The observed specimens never left a healthy host willingly; when, in aquarium experiments, various red substrates or mucous sea cucumbers were offered beside H. sanguineus, the shrimp always chose the nudibranch. However, dead or injured and motionless slugs were abandoned. Two days after the death of a nudibranch, its commensal shrimp accepted the brown synaptid Euapta godeffroyi as host; on a previous occasion, a shrimp was found living on this latier species in the reef. The adaptation of P. imperator to living on the temporarily free-swimming H. sanguineus apparently represents a special evolutionary stage compared with that of other members of this family, which are mostly commensal with sessile hosts. Only palaemonid cleaner-shrimps feed briefly from free-swimming substrates.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft