| Parasite | Nymphonella tapetis |
|---|---|
| Taxonomy | Arthropoda, Pycnogonida, Pantopoda |
| Hosts | Manila clam (Ruditapes philippinarum), Jedo Venus clam (Protothaca jedoensis), Theora fragilis, Hiatella orientalis, etc |
| Infection site | Pallial cavity |
| Clinical sign | One to several tens of Nymphonella tapetis (0.5-5 mm) are observed in the pallial cavity, gill and lavial palp of bivalves (Figs. 1 and 2). |
| Parasitology | Larvae of Nymphonella tapetis suck nutrients from bivalves by proboscis borrowing into the host tissue and grow (Ogawa & Matsuzaki, 1985). It was considered that the adult is free-living and burrows into the sand, but Taru et al. (2007) reported that some larvae developed to adults in the clam. The parasite is probably a euryhaline organism because it lives in the intertidal zone. In addition, it may show a tolerance to the low temperature (13 C) (Taru et al., 2007). |
| Pathology | Parasite adversely affects not only the ingestion, but also the respiratory system of the host because the parasite occupy the pallial cavity, resulting in inhibition of water flow inside the shell (Taru et al., 2007). Infested fish are often led to the death. |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. In addition, Infected bivalves are not toxic (neither diarrhetic nor paralytic). |
| Diagnosis | Spider-shaped parasites can be visually observed in the pallial cavity. The body of N. tapetis is composed of the head, thorax consisting of 4 segments and shrunken abdomen. Each segment of the thorax has a pair of long appendages. |
| Other information | In July 2007, the local fishermen at Chiba Prefecture, Japan gave up the fishing of Manila clam, because a mass mortality of the clam caused by the parasite occurred from the end of June in the Banzu-Tide-Land in Tokyo Bay. It is unknown why so many parasites appeared at that time. There is a possibility that the parasite was introduced from other areas (Taru et al., 2007). |
| References |
Ogawa, K. and K. Matsuzaki
(1985): Discovery of bivalve-infesting Pycnogonida, Nymphonella tapetis, in a new host, Hiatella orientalis. Zool.
Sci., 2, 583-589. Taru, M., S. Nakayama, H. Takasaki and T. Komai (2007): Circumstances that vivalves are infested by Nymphonella tapetis at the Banzu-Tide-Land in Tokyo Bay. Umiushi Tsushin, 56, 4-5 (In Japanese). |
Fig. 1. Manila clam parasitized by a sea-spider.
Fig. 2. Nymphonella from Manila clam.
(Photos by K, Momoyama)
