Gill-cleaning mechanisms of the burrowing thalassinidean shrimps Nihonotrypaea japonica and Upogebia major (Crustacea: Decapoda)

Abstract

The burrowing habits of thalassinidean shrimps presuppose their high susceptibility to the deleterious effects of gill fouling by particulate debris and epibionts. The structures and strategies used to prevent gill fouling were examined in Nihonotrypaea japonica and Upogebia major by morphological inference and aquarium observations. The gill complement of both species consists of 10 arthrobranchs, with flattened filaments of the phylloid trichobranch type. Nihonotrypaea japonica and U. major lack passive gill-cleaning setal systems in the branchial chamber, but were found to actively groom gills by inserting and brushing the gill filaments with a pad of dense setae on the distal segments of their fifth pereiopods (P5 brush). Grooming setae of the P5 brush in N. japonica are of serrate and plumose types, whereas they are serrate and pappose in U. major. Serrate setae with distally curved spiniform denticules were morphologically similar in both species. Phylogenetic mapping of the gill-cleaning mechanisms suggests that gill-cleaning characters are homoplasic and systematically conservative among the families of the Thalassinidea.