The morphology and ecology of Dipolydora armata (Polychaeta, Spionidae) from the western Mediterranean Sea

The cosmopolitan spionid Dipolydora armata is a dominant species of epifaun a on Thais haemastoma shells in the western Mediterranean Sea. Some charact ers, particularly number, thickness and arrangement of notopodial spines, w ere extremely variable among specimens. Three morphological forms were dist inguished based on the general appearance of the bundles of spines; one for m possesses at least one bundle of stout spines, whereas bundles of medium spines or thinner acicular spines characterise the other forms. Differences in prostomial shape, as well as in the extension and form of the caruncle, were artefacts (preservation or angle of observation). The present study s upports D. rogeri as a junior synonym of D. armata. D. armata was regularly found on shells inhabited by hermit crabs (Calcinus tubularis, Clibanarius erythropus) and on damaged, empty shells. Abundance, dominance, size frequ ency, occurrence of larvae and occurrence of regenerated specimens varied, possibly as a result of fouling strategy and recurrent settlements.