Social structure, sexual dimorphism and relative growth in the ghost shrimpCallichirus seilacheri(Bott, 1955) (Decapoda, Axiidea, Callianassidae) from the tropical eastern Pacific

We analyzed the social structure, sexual dimorphism and relative growth in the burrowing shrimp Callichirus seilacheri from the tropical eastern Pacific. To this end, 456 individuals of C. seilacheri were collected during monthly sampling from December 2011 to November 2012. No shrimp pairs or burrows inhabited by more than one shrimp were detected during the study period. Males were significantly smaller than females, denoting sexual dimorphism with respect to body size. In many juvenile males and females, the size of the right and left claws was the same, whereas in others the largest cheliped was located on the right or left side. Analysis of allometric growth between cheliped carpus length and cephalothorax length revealed an isometric relationship in juveniles of both sexes and adult females and positive allometric growth in adult males. The adjustment of the above relationship by the Somerton's method, denoted the existence of two main phases of growth related to sexual maturity, with transition points between juvenile and adult phase at 12.3 mm and 12.0 mm of body size for males and females, respectively. The observations on social structure, sexual dimorphism and relative growth of C. seilacheri argued that this species is polygamous. Furthermore, the high frequency of solitary females found brooding embryos suggested that males might roam among galleries in search of receptive females.