Preliminary approaches on pseudoshell utilization by the hermit crab Sympagurus dimorphus (Studer, 1883) (Anomura, Parapaguridae) from South Atlantic

SCHEJTER L.; MANTELATTO F.L.

Guarapari, Brasil

Congreso; IV Congresso Brasileiro sobre Crustáceos; 2006

The genus Sympagurus Smith, 1883 was recently redefined to include 13 species that inhabit the lower continental shelf and upper slope regions of most world oceans in depths from 80 to 2500m. Some species live in striking symbiosis with zoanthid species, pseudoshell-producing anthozoans. Although the mechanism of shell occupation processes by the hermit crabs have been well investigated worldwide, systematized information on these parameters for Sympagurus species versus pseudoshell are scattered and poorly known. We furnish here some information on utilization by Sympagurus dimorphus from Argentinean waters. The studied organisms were part of 17 benthic samples taken with a dredge during a research cruise of the Patagonian scallop with the R/V “Capitán Cánepa” (INIDEP) in the area comprised between 39º24’ and 37º27’S and between 55º00’ and 56º04’ W, between 91 and 123 m depth, in October 2005. A total of 82 specimens of S. dimorphus were collected, 73 (89%) of whom were living in symbiosis with de zoanthid (the other 9 were living inside Fusitriton magellanicus shells). From these organisms, 40 (50,79 %) were males, 13 (17,81%) were non-ovigerous females and 20 (27,40%) were ovigerous females. Nine gastropod shells were found as terminal part of the pseudoshell, all of them totally covered with colonies of Epizoanthus paguricola. In general, significant occupation was observed for Naticidae gastropod species. The number of epizoanthid polyps per individual increased in relation of the hermit crab size. The puzzling association between hermit crab, shell and zoanthid presumably occurs during the hermit juvenile phase when the crab occupies a small shell, and a zoanthid larva settles on it. Later, when the hermit grows and the shell becomes too small for it, the zoanthid begins to enlarge as the same form of the terminal gastropod shell, adding new whorls to it. This hypothesis may be acceptable since the hermit does not have to search for a new shell and the crab lives in a spiral cavity in the cartilaginous colony and both benefit from this. In the studied area and also in other southern Patagonian scallop beds from Argentina, Sympagurus dimorphus is found living associated with Epizoanthus paguricola rather than in empty gastropod shells. This is part of an on going project to improve the knowledge of the biology of this poorly studied group of hermit crab.