Gill-Cleaning Mechanisms of the Mud Lobster Thalassina anomala (Decapoda: Thalassinidea: Thalassinidae)

Abstract

The gill-cleaning mechanisms of the mud lobster Thalassina anomala were examined. The gill complement consists of 12 arthrobranchs and 5 podobranchs, both having cylindrical flattened filaments. Morphological inference suggested passive gill-cleaning mechanisms involving various setal systems; multidenticulate setae (on scaphognathite, setobranch, distal epipod), pappose setae (on coxae, proximal epipod), serrate setae (short setal tufts on limb coxae), and plumose setae (on carapace fringe). Smooth setae were found on the thoracic epimeron (inner wall of the branchial chamber) and inner branchiostegal margin. Small lamellar protrusions on the pereiopodal arthrodium were noted bearing dense pappose setae. The multidenticulate scaphognathite and epipodal setae were serrate distally. The digitate scale setules of multidenticulate setobranch, epipodal, and scaphognathite setae shared similarities: (1) digitation pattern gradually changes distally from angular to linear, (2) proximal setules incline toward the base while distal setules incline toward the tip with overlapping inclinations in a transition zone, and (3) setule density increases distally on the setal shaft. The multidenticulate scaphognathite setae have a V-form spiral arrangement on the distal part of the shaft, which is atypical in decapods. Aquarium observations did not show active gill cleaning by thoracic limbs, but general body grooming and respiratory reversal were observed. The phyletic relationships of gill-cleaning mechanisms, with notes on branrchial morphology, are discussed.