The Secondary Sexual Characters found in the Lined Shore Crab, Pachygrapsus crassipes, with Special Regard to the Copulatory Organs

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  • CHIBA Akira
    Department of Biology, Faculty of Science, Niigata University
  • HONMA Yoshiharu
    Department of Biology, Faculty of Science, Niigata University

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  • イワガニの第二次性徴とくに腹肢の組織学的観察
  • イワガニ ノ ダイ2ジ セイチョウ トクニ フクシ ノ ソシキガクテキ カンサツ

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The present paper deals with the morphological observation of several sexual characters in the lined shore crab, Pachygrapsus crassipes (GRAPSIDAE, BRACHYURA), that is widely distributed along the rocky beaches of the Japanese Islands. About 180 individuals ranging from 11 to 38mm in carapace width were collected from the coast of Niigata City facing the Japan Sea. The period of collection extends from April to November, 1969. In addition, several specimens were obtained on the coasts in the vicinity of the Sado Marine Biological Station of Niigata University located on the west coast of the Japanese mainland, and the Misaki Marine Biological Station of Tokyo University in the Pacific side. The secondary sexual characters were detected in several portions of the body. As to the size and coloration, chelipeds of male crab are larger and more deep-red than those of female. Similarly, the carapace of male with more obtuse angle of postero-lateral margin is darker in tint than that of female. As in the cases of the other crabs, a most remarkable sexual difference is found in the feature of abdomen and thoracic sternum. The abdomen of the female, broad and semicircular in shape, is equipped with four pairs of the pleopods which are adorned richly with the long and soft hairs. These structures are suitable for the holding and nursing of the developing embryos. On the other hand, the male abdomen is characterized by the copulatory organ that consists of the primary and secondary pleopods. While the base of primary pleopod is provided with a bundle of soft hairs, a spine and bristles are encountered in its terminal portion. Further, a deep groove in a similar condition of the sheath is located in the basal portion of the primary pleopod. When the mature male inserted the secondary pleopod in needle shape into this groove, the semen might be forwarded to this groove through the penis. Following this, the semen flows to the terminal spine by way of the chitinous duct. Finally, the semen is transported to the spermatheca of the female crab. Neither spermatophore nor its related material was detected anywhere in the gonoducts of this crab. However, no peculiar structures that correspond to these materials could be seen in the copulatory complex. The male primary pleopod consists of the loose connective tissue, and the follicles in rosette manner stained with acidic dyes are found near the basal groove.

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