Morphological and functional characteristics of setae involved in grooming, water uptake and water circulation of the soldier crab Mictyris guinotae (Decapoda, Brachyura, Mictyridae)

Abstract

This study was focused on the relationship between behaviour and morphological characters of the soldier crab Mictyris guinotae, using a functional morphological approach. The behaviour patterns of M. guinotae involved in water uptake and water-circulation were recorded by video camera and the setae involved in those two activities were described in detail. Furthermore, the crab’s grooming behaviour engaged in the cleaning of the surface of the third maxilliped was determined. The setae were classified into six types: denticulate, pappose, plumose, normally setulate, serrate, and simple setae. Among these, the denticulate setae were found on the chelipeds and the simple setae on the posterior margin of the carapace and on the anterior border of the first abdominal somite. M. guinotae inserted the setae located on the posterior border of the carapace margin and the anterior border of the first abdominal somite into the sandy substratum, and expelled water from its exhalant apertures and mouthparts. The water then flowed along the surface of the third maxilliped onto the abdomen. The crab exhibited a grooming behaviour to clean the surface of the third maxilliped after expelling water, by using the carpus and propodus of the cheliped when the surface of the third maxilliped had become covered by mud. We conclude that simple setae may have the function of collecting water from the substratum by capillary action, and the denticulate setae apparently have a grooming function. Moreover, also (the flow of) water may increase grooming efficiency, when the flow continues as the crabs groom the surface of their third maxilliped.