Morphometric Relationships Between the Hermit Crab Isocheles sawayai (Forest & Saint Laurent) (Crustacea Anomura Diogenidae) and its Shell from Southern Brazil

A study on morphometric relationships between the hermit crab Isocheles sawayai and its shell in a population from Paraná-Santa Catarina States coast was carried out. Hermit crabs from the by-catch of shrimp fishing (4-15m depth) were collected. Cephalothoracic shield length (CL) and width (CW) from hermit crabs and total length (SL), aperture length (AL) and weight (SW) from shells were taken. A total of 266 hermit crabs occupying eight species of shell Buccinanops lamarckii, Dorsanum moniliferum, Oliva reticularis, Olivancillaria steeriae, O. urceus, Polinices hepaticus, Semicassis granulatum and Stramonita haemastoma were obtained. Males (N = 189) that dominated strongly (1M : 0.4 F) occupied eight shell species, while females (N = 76) occupied only six. There was only one intersex individual that occupied a Stramonita shell. Contrarily to intertidal populations, O. urceus was the most frequently occupied shell by males (57.14%) and females (62.33%) in this studied area. Due to the smaller size of females (mean CL 5.19±0.84mm), these ones occupied shells of a smaller size than males (mean CL 6.49±1.14mm). The highest O. urceus shell frequency of occupation is connected to the hermit crab ́s life style: it is a filter feeding species and its shell remains totally buried in the sandy substratum having only its cephalothoracic appendages free. The heavy shell of this gastropod (highest SW/SL) favors the stability in strong current water conditions, as it functions as an anchorage for this semi-buried hermit crab.