Three species of mytilid bivalves(Mytilus edulis aoteanus, Perna canaliculus, Aula‐comya maoriana)co‐exist in the eulittoral zone of some rocky shores in New Zealand. However, their distributions within this zone show micro‐geographic differences. To determine the possible role of behaviour on these diiferences, separate experiments on the species’ abilities to crawl out from under gravel and to distribute themselves in mixed‐species clusters were performed. When small mussels (1–2 cm long) were covered with 3 cm of pea gravel (0.3–0.8 cm grain size),P. canaliculuscrawled to the surface much more rapidly than did the other 2 species, which were generally similar in crawl‐out ability. When numbers of small mussels (1–4 cm long) of the 3 species were mixed together in various combinations and held in sea water,A. maorianapredominated inside the resultant clusters, whereasP. canaliculuswas judged to be slightly more abundant thanM. e. aoteanuson the outside of such clusters.