| Parasite | Unidentified rhizocephalan |
|---|---|
| Taxonomy | Arthropoda, Crustacea, Maxillopoda, Cirripedia, Rhizocephala |
| Host | Striped shore crab (Pachygrapsus crassipes) |
| Infection site | Abdomen of crab |
| Clinical sign | A bean-shaped parasite is observed in the abdomen of crab (Fig. 1). |
| Parasitology | This parasite is a parasitic crustacean taxonomically related to acorn barnacle, but lacks appendages and segmentation due to the specialization for parasitism. The body is composed of an externa (sac-shaped outer part of the body) and an interna (root-shaped inner part). The externa is occupied by the ovary. A nauplius or cyprid hatches inside the externa, swims and settles on crab. After penetration into the body of the crab, a tumor-like interna develops following to the formation of the externa in the abdomen of the host. The externa is fertilized followed by settlement of a male larva (Takahashi, 2004). |
| Pathology | Parasitized crab is led to the castration, resulting in loss of reproduction ability. The parasite induces a male host to feminize in morphology, e.g. the larger abdomen and smaller claws (Takahashi, 2004). |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Check the externa of the parasite in the abdomen of crab. |
| Other information | It is considered that behaviors of a host crab are manipulated by the parasite, e.g. the host cleans the surface of an externa and helps the release of the parasite larvae (Takahashi et al., 1997). |
| References |
Takahashi, T. (2004): Rhizocephalan, a parasite manipulating the host sex. Field Parasitology (ed. by Nagasawa, K.), Tokai University Press, Kanagawa, pp. 81-94. (In Japanese)
|
Fig. 1. Rhizocephalans parasitizing the striped shore crab.
(Photo by K. Ogawa)
