A new record of the endosymbiont polychaete Veneriserva (Dorvilleidae), with description of a new sub-species, and relationships with its host Laetmonice producta (Polychaeta: Aphroditidae) in Southern Ocean waters (Antarctica)

Abstract.

A new record of the genus Veneriserva Rossi, 1984 (Polychaeta: Dorvilleidae) is reported, as an endosymbiont in the coelom of the polychaete Laetmonice producta Grube, 1877 (Aphroditidae) in the eastern Weddell Sea and off King George Island (Southern Ocean, Antarctica). The specimens studied were very similar to Veneriserva pygoclava Rossi, 1984; however, due to the greater morphological variability and larger dimensions of our specimens, as well as different host species and geographic locations, a new sub-species, V. pygoclava meridionalis, was erected. A total of 842 specimens of L. producta were examined, 163 of which hosted 209 symbionts (183 in the Weddell Sea samples and 26 in the King George Island samples). Symbiont prevalence was higher in the Weddell Sea samples, and increased with depth (max. 51% at stn 14, 850 m depth). Symbiont intensity was equal to one for 78% and to two for 19.6% of all hosts examined; a maximum of six symbionts per single host was observed. Mean symbiont density was equal to 0.36 and 0.07 for the Weddell Sea and King George Island host populations, respectively. A weak linear relationship was found between symbiont and host size. Eight symbiont specimens (all found at a single station, 850 m depth) were bearing eggs, ranging between 10 and 200 µm in diameter, while 13 specimens were observed in regeneration of the posterior part, suggesting the occurrence of both sexual and asexual reproduction. The way of feeding is still not clear; reduction of the jaw apparatus suggests a parasitic host–symbiont relationship, however, no evident damage was observed in the tissues of the host. These results point out that occurrence of polychaete endoparasites in large aphroditids may be a more frequent and widespread phenomenon than previously believed, and that more attention should be paid to this aspect also in temperate and tropical aphroditid species.