Abstract
The development of the planktonic veliger larva ofMytilus edulisL. culminates in a swimming crawling stage during which the foot is of considerable importance in the selection of a settlement site. This stage has been described for many other bivalves (see Bayne, 1965) and has been given the term ‘pediveliger’ by Carriker (1961). The pediveliger ofMytilus edulisis negatively phototactic and positively geotactic during velar swimming (Bayne, 1964b) and is usually confined to water layers close to the substratum. The foot may be protruded during swimming and if it comes into contact with the substratum it adheres and a period of crawling commences. During crawling the larva progresses on the ventral or posterior surface of the foot by means of ciliary and muscular action. Crawling may result in attachment by secretion of the first byssus thread or alternatively the foot is withdrawn and velar swimming is continued until the next exploratory crawling phase.Mytiluslarvae attach most readily to filamentous substrates in the field (Blok & Geelen, 1958; Bayne, 1964a).
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