- 一般社団法人 日本甲殻類学会
- vol.3, pp.52-60, 1967
This paper deals with the sacculinization occurred in a male of the pea crab, Pinnetheres sinensis Shen. The specimen was found living commensally within the mantle cavity of the common bivalved shell, Mytilus edulis Linne, obtained on the coast of Tokyo Bay in October, 1964. The body of the adult normal male of Pinnotheres sinensis is rather flat and solid, much smaller than the normal female which has the grobular and soft-shelled body. Even in the largest male, the length of carapace is less than one half that of the fully grown female. In the male, the chela is somewhat thickset compared with that of the female and its propodus furnished with 10-13 setae near the distal end of the anterior border. In second and third pairs of the male ambulatory legs, the carapus is crossed by an oblique row of long feathered hairs, and the propodus fringed with same hairs along the anterior borders. The dactylus of all pairs is claw-shaped and shorter than the propodus. In the female, the dactylus of the last ambulatory leg is rod-shaped and longer than the propodus, furnished with longish hairs along the inner border, with short hairs around the whole surface in distal half. The width of the male abdomen is much narrower than that of the female-about one fifth the length of the carapace, and its sixth abdominal segment has a hook-shaped process on the lateral margin. Of the two pairs of male pleopods, the posterior one has a short flatty exopodite. Of the four pairs of female pleopods, the posterior two are uniramous and has no exopodite (Fig. 1). The external morphological modifications are seen in the male, by sacculinization, as shown in the following: a) The size of the body becomes comparatively larger than in the normal male, and its exoskeleton becomes softend as in the female body (P1. VI). B) The chela becomes somewhat slender and the setae on the propodus are replaced by soft longish hairs, covering the distal surface of both fingers (Fig. 2, 3). C) The long feathered hairs seen on the second and third ambulatory legs are worn out and the dactylus of the fourth ambulatory leg is longer than the propodus, furnished with long hairs as seen in the female (Fig. 2, 1). D) The width of abdomen is broadened; the lateral margin of the sixth segment becomes entire and with marginal hairs (Fig. 3). E) No change of form seems to occur in the first pleopod except for its tip. The carified bridge at the foot of the first pleopod is rudimented. The exopodite of the second pleopod is well developed and covered with long soft hairs. No pleopod is seen in the third abdominal segment, while in the fourth abdominal segment, a uniramous appendage is seen on the right side (Fig. 3 and 4). The internal morphological modifications are seen in testis and midgut gland. These organs are entirely rudimented, being only represented by withered cells. The roots of the parasite glowing thickly around the vas deferens, the midgut gland, the anterior portion of intestine, and the thoracic ganglion. In vas deferens, however, sperms and spermatophores are still seen filling the duct. The penetration of roots of the parasite into the thoracic ganglion has already been investigated by the previous authors (MATSUMOTO K. (1952) and HOSHINO K. (1962)), so the author's present investigation is confined to that of the vas deferens.