Pseudomastus deltaicus , gen. et sp.n. (Polychaeta: Capitellidae) from a shallow- water bay in the North- Western Mediterranean Sea

Abstract

The Els Alfacs Bay (Ebre Delta) located on the North- East coast of the Iberian Peninsula (Western Mediterranean, 40”33’-38’N, W32’44’E) is a semi-enclosed shallow water area which can be characterized as a ‘paralic’ environment (sensu Guelorget & Perthuisot 1983): although its hydrographic regime is basically marine, it is clearly influenced by the terrestrial freshwater inputs reaching the bay during the spring-summer period (Palacin et al. 1991). Several recent studies have been documented on the zoobenthos of the bay (Soler-Martinez 1988; Palacin 1990; Palacin et al. 1991; Capaccioni-Azzati 1987; Capaccioni & San Martin 1989-1990; Martin 1990, 1991; Martin & Giangrande 1991). The last five, in particular, focused on its polychaete fauna. Paralic environments like Els Alfacs Bay could offer particularly favorable sites for speciation because they are virtually isolated, having high levels of environmental stress. Among the results of the aforementioned studies, two new species of Polychaeta (Capaccioni & San Martin 1989-1990; Martin & Giangrande 1991) and 13 of Nematoda (Palacin 1990) have been identified. In 1984-1985, a large number of incomplete specimens of a Capitellid species were collected from muddy bottoms of the Els Alfacs Bay. They were identified initially as Pseudoleiocapitella fmiveli (Cap;iccioni-Azzati 1987). Additional entire spccimens of the same species were obtained in 1987. l’hc number o f 12 thoracic sctigci the different setal pattern, together with the prcscncc o f an abdominal branchiatc region, allow us to separate these spccirncns from all previously described gcnera and specics, although similarities can be lound with species of Pseudoleiocapitella and Mastobrunch us. Con sc q uc n t I y , ;I new genus and species of Capitellidae is described.