Morphological notes on the mouthparts of decapod crustacean larvae, with emphasis on palinurid phyllosomas

Abstract

Some topics in the morphological study of mouthparts of decapod larvae, consisting of labrum, mandible, paragnath(= labium)and maxillule, are briefly reviewed. The morphological features of larval mouthparts are compared topographically in main decapod groups. Among them, two unique types are noted: palinurid and some thalassinid mouthparts. Palinurid phyllosoma larvae have dorsoventrally flattened mandibles sandwiched and covered between a large labrum and paired paragnaths. Furthermore, otherposterior appendages, maxilla and maxillipeds, are placed far apart from the position of mouthparts. Phyllosoman mouthparts of Panulirus japonicus by VTR showed that active movements of labrum and paragnaths. Morphological characters of phyllosoman mouthparts suggest that microphagus feeding in their larval life based on Alexander's(1988) comments. In the symmetry of larval structures, two thalassinid families, Laomediidae and Thalassinidae, the zoeal larvae have remarkably asymmetrical mandibles and paragnaths. At present nothing is known on feeding mechanisms by those unique mouthparts. In addition, Lacinia mobilis is found in left mandible of some caridean zoeal larvae and we have no information on the role of this structure which is lacking in adult phase of decapod mouthparts.