NOTES ON OCCURRENCE. FEEDING AND SWIMMING BEHAVIOUR OF NOTARCHUS INDICUS AND MELIBE. BUCEPHALA AT ELAT, RED SEA (MOLLUSCA: OPISTHOBRANCHIA)

ABSTRACT

The simultaneous occurrence of algae and the slugs Notarchus indicus and Melibe bucephala in Elat is pointed out. Both slugs are calm-water types and profit from the detritus layer on the algae. Notarchus indicus scrapes off the food from more or less flat surfaces using its radula. Melibe bucephala, which has no radula, is conspicuous for its specialized method of taking detritus from filamentous substrates. This feeding behaviour is permitted by a special organ, the oral hood, which can take in soft tender food particles by enclosing them. Melibe bucephala swims by bending its body laterally. Notarchus indicus swims by the propulsive thrust of a water jet expelled from the parapodial cavity. It is suggested that Notarchus indicus in the adult stage is regularly distributed to new habitats by swimming and floating in sea currents.