Functional morphology of the Chelipeds, mouthparts and gastric mill of Ozius truncatus (Milne Edwards) (Xanthidae) and Leptograpsus variegatus (Fabricius) (Grapsidae) (Brachyura)

Abstract

Field and laboratory observations show that O. truncatus is a predator on gastropod molluscs, using dimorphic crusher-cutter chelipeds to remove the shell. The soft gastropod body is then presented to the maxillipeds. The third maxillipeds and mandibles tear the food, but the fragments reaching the foregut are still relatively large. The gastric mill ossicles of O. truncatus are robust, with few setae.

L. variegatus is an opportunistic omnivore using equal cutting-scraping chelipeds in an alternating action, mainly in plucking and scraping algae. The food fragments reaching the maxillipeds are finely shredded by the chelipeds. The small food fragments are ingested directly, being pushed into the mouth by the mandibular palps. The maxillipeds and mouthparts do not triturate the food. The gastric mill ossicles of L. variegatus are finely toothed and setose. Analogous functional relationships between ingestion mechanisms and gastric mill occur in Anomura. The need for further studies on Brachyura is stressed.