Pseudoshell relationship in question: the deep water hermit crac Sympagurus dimorphus (Studer 1883) and Epizoanthus sp. in Southwest Atlantic Ocean.

SCHEJTER LAURA; MANTELATTO F.L.

Coquimbo, Chile

Congreso; The Crustacean Society. Mid Year Meeting; 2007

Sympagurus dimorphus is a scarcely studied hermit crab distributed in deep waters of southern hemisphere. It is one of the 17 recognized species of the genus, and about 1/3 of which are known to establish symbiosis with zoanthids. The records of the zoanthid-hermit crab associations deal only with reports of this phenomenon with no detailed information. We describe, for the first time, the pattern of shell-like colonies of Epizoanthus sp. associated with the hermit crab S. dimorphus inhabiting in the Patagonian scallop (Zygochlamys patagonica) fishing grounds ( ~ 100 m depth) in the Argentine Sea. To evaluate a possible effect of the initial gastropod shell and the hermit crab presence on the morphology of the zoanthid colony, morphometric relationships were assessed. A total of 260 specimens (137 males and 123 females) of S. dimorphus were collected, 240 (92.3%) of whom were living in symbiosis with Epizoanthus sp.; the remain 20 (7.7%) were living inside Fusitriton magellanicum shells. As the initial structure of the pseudoshell, 12 different gastropods species were found (all were almost totally covered with colonies of Epizoanthus sp.). A selection process of the initial shell is evident, as Naticidae are not the most common gastropods in the benthic community sampled, but was the most used (>60%) by hermits. 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. 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 that seemed to be slightly different depending on the initial gastropod. This is part of an on going project to improve the knowledge of the biology of this intriguing group of hermit crabs.