Ökologisch‐funktionsmorphologische Untersuchungen an karibischen Krabb en (Decapoda, Brachyura) I.Percnon gibbesi(H. Milne‐Edwards, 1837) (Grapsidae, Plagusiinae)∗

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Abstract
Researches on the ecology and function morphology of Caribbean crabs (Decapoda, Brachyura) I. Percnon gibbesi (H. Milne‐Edwards, 1837) (Grapsidae, Plagusiinae) A population of juvenile Percnon gibbesi was observed in the rocky sublitoral zone at the Caribbean coast of Columbia. The animals were found exclusively in the immediate vicinity of the sea‐urchin Diadema antillarum. They obviously used the shelter of the long spines as a protection against predators. When a sea‐urchin was removed, the associated crabs were inevitably eaten by fish. The chelipeds show a marked sexual difference, the chela being much broader in the male than in the female. An area covered with long thin setae is only present in the male. These differences are taken to imply that the chelipeds play an important part in courtship and/or copulation. The peraeopods and the dorsal surface of the carapace show an elaborate pattern of rows and fields of feathered spines. It is hypothesized that these are used as a suspension‐filter. The 1st antennae are, as in all Plagusiinae, situated in dorsal slits of the frontal margin of the carapace. They were observed to perform permanently quick flicking vertical strokes. After a number of strokes they are brushed through the maxillipeds. The exopodite is bent in form of a semi‐circle and ventrally carries rows of long thin setae which are arranged in a fan‐like fashion. This fan displays a conspicuous bright yellowish colour when the antenna is moved up and down. The antennal behaviour can be interpreted in two ways: either it functions to attract small fish which are then caught and eaten, or the antenna is used as an active suspensions‐filter. These two possibilities do not exclude each other. The mouthparts show, by their rich equipment with rows of setae, that they are used for handling food which consists of small particles. This agrees well with the functional interpretation of the setal armature of peraeopods and carapace and of the described antennal behaviour, and it strengthens the hypothesis that Percnon gibbesi acquires the bulk of its food by suspension‐filtering.