小笠原諸島のカニ類,II : 魚類の胃中より得られたカニ類,第1報

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This paper deals with the decapod crustaceans obtained from the stomachs of four species of fishes collected at the rocky bottom of the shallow water. The fish species are Epinephelus fasciatus (FORSSKAL) of the Serranidae, Gymnocranius japonicus AKAZAKI and Lethrinus variegatus VALENCIENNES Of the Lethrinidae, and Parupeneus barberinoides (BLEEKER) of the Mullidae. All the species are useful for food, and the first or the blacktip rockcod is the most abundant along the entire coasts of the islands and islets of the Ogasawara Islands. Among these only in the second species three specimens are available for the examination of the stomach contents. The identification of the species is rather difficult in some cases in which there are only the fragments of the carapace and chelipeds. In this paper altogether 20 crab species including some questionable ones were identified, and two pairs of chelae obtained from G. japonicus, which are probably referred to those of Lissocarcinus or allied genera of the Portunidae, are remained uncertain. There are otherwise a large and a small chelae of snapping shrimp referable to Alpheus, a chela of Callianassa which is an anomuran decapod called mud or ghost shrimp, two specimens of Munida or lobster krill, a right or small cheliped of hermit crab referable to Calcinus, and two specimens of grapsid megalopa larvae. Although 123 crab species have hitherto been known from the Ogasawara Islands, it is remarkable that 11 of 20 species identified at present are new to this area. This fact indicates that the rocky bottom of the shallow or rather deep water is scarcely exploited. This sort of reports may be therefore of certain use not only for the systematics of the crustaceans, but also as the indicators for the ecology of the fishes and crustaceans. As summarized in Table 1, it is remarkable that 7 of 20 species are referable to the Majidae, representing 35% of the species recorded. The families subjected to food of fishes are the Dromiidae, Majidae, Parthenopidae, Portunidae, Xanthidae, Goneplacidae, so that the ratio of the known species of the Majidae among these families are only 14%. On the other hand, the low percentage of the Xanthidae for food is also remarkable, being 30% at present contrary to 69% in the known species of the above families. This fact may be attributed to the different habit and habitat, and it is briefiy mentioned that the camouflage with the seaweed, sponge or other inorganic matter may be not always an effective means for the defence against the fishes. The relation between the crab and fish species is summarized in Table 2. This suggests that as for the habit of food search Parupenus barberiwoides may be somewhat different from Gymnocranius japonicus and Epinephelus fasciatus.

小笠原諸島のカニ類,II : 魚類の胃中より得られたカニ類,第1報

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