ECOLOGY AND DISTRIBUTION OF THE DIURODRILIDAE (POLYCHAETA), WITH REDESCRIPTION OF DIURODRILUS-BENAZZII

The ecology and distribution of Diurodrilus species have been studied after a bibliographic review. The species of this genus are often rest ricted to the upper moist sand substratum (medium water level, D. subt erraneus, D. ankeli, and D. benazzii), or to the lower midlittoral and upper sublittoral (D. minimus, and D. dohrui). In natural environment s a single species occurs at each horizontal level. The distribution p attern between upper and lower levels may be controlled by physical fa ctors. Interspecific competition between congeneric species of Diurodr ilus may be considered as a possible cause controlling populations wit hin each horizontal sandy beach level. It is possible to identify morp hological differences between species inhabiting each horizontal level of a sandy beach. In the lower level, always scoured by the waves, Di urodrilus minimus and D. dohrni have well developed toes, reacting wit h adhesion to increased water currents, while in the more stable upper level, D. benazzii and D. subterraneus display reduced adhesive toes, both in size and number. Diurodrilus benazzii was collected from the midlittoral phreatic system in a sandy beach at the Gulf of Valencia ( W. Mediterranean). Since no information is available on taxonomical ch aracters of D. benazzii, e.g., the sensorial pattern, ciliophores, or ventral ciliation, this paper provides a redescription of the species, comparing the taxonomically relevant characters of all known Diurodri lus species.