Decorating behavior of the majid crab Hyastenus diacanthus

概要

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The decorating behavior of 17 newly molted individuals of the majid crab Hyastenus diacanthus (De Haan, 1837) was recorded on VTR. The crabs attached various living materials to hooked setae on the carapace and walking legs after careful selection by the chelae and processing with the mouthparts. The crabs used chelipeds in a fixed way in the attachment process. Except for the horn and spots on the carapace, the crabs attached materials using the chelipeds of the opposite side. Newly molted crabs had almost finished attachment within 2 hours, but the crabs continued to work sporadically for another 1 or 2 hours. The average frequency of attachments was 91 (N=7). The hooked setae cover only a portion of the body, and other areas, except for the tips of the chelae, are covered with barbed setae. The barbed setae hold the materials, which grow outside of the hooked setae sites. The crabs were indifferent to the settlement of larvae of sessile animals, such as barnacles, and did not remove them. Consequently, portions of the crabs were covered with sessile animals. The slender setae on the dactyl of walking legs and the short setae in the pits of chelae are likely sensory organs to detect suitable materials for attachment.