The biology, ecology and behaviour of theBivalveMysella bidentata(Montagu)

Abstract

Mysella bidentata is a euryvalent species. Its distribution in the N. Øresund 3-4 months after settling is positively correlated with the density of adult Amphiura filiformis. In the laboratory, Mysella prefers to live in the oxydized layers around the burrow of Amphiura. Dense Amphiura populations enlarge the water-sediment interface and thereby the oxydized layers and the microbial activity. This benefits Mysella which obtains protection from surface-hunting predators and additional supply of food. In their second year the bivalves are functional males, and when three years old and 3 mm long they are hermaphrodites. Males produce fertile and oligopyrene sperm simultaneously. Sperm transfer involves sperm bags and receptacula seminis, and is thus time-independent of egg-spawning. Mysella reacts to gravitation by positive or negative taxes, and to direction of water flow by positive tropo-taxis or compass reactions. Chemical stimuli from a predator (Astropecten) evoke direct orthokinesis. Stimuli from a host (Amphiura) evoke direct orthokinesis and direct klinokinesis as well. A model links the natural hierarchy of responses and behavioural patterns in Mysella to fundamental physiological functions, survival mechanisms, site selection and intraspecific regulation in consistent order. The model may be adapted to fit other species for various purposes. Within the Montacutidae, changes in host selection and behaviour have been more decisive for evolution and speciation than changes on other organismic levels. Earlier descriptions of growth, biology and behaviour of A. filiformis and A. chiajei are revised.