On a New Species of Malacobdella 

 (M. japonica). 

 By U. Takakura. 



Zool. Institute, Imp. University, Tokyo. 

 With Pl. VU. 



Since last April I have devoted myself to the investigation of a 

 Malacobdella, which lives in the mantle cavity of Mactra sachalinensis, 

 Japanese name, " Ubagai" or " Hokkigm", and. have found out that 

 notwithstanding a close resemblance of its external form to that of M. 

 grossa, Müller, its internal structure presents some features sufficiently 

 different from that of the latter species, to justify its separation into a 

 distinct species. 



M. japonica, as I propose to call our species, lives in the mantle 

 cavity of Mactra sachalinensis, which is found in the northern part of 

 our country. The specimen I used were all collected on the shore of 

 Kujükuri on the Pacific coast of the province Shimousa. Almost every 

 individual of Mactra from that locality contains the parasite. Of the 

 56 shells, which I examined, 54 were found to he infected. As v. 

 KENNEL found in Cj/prina islandica, adult worms live always single 

 in one shell, while if two or more live together in one shell these 

 are invariably young individuals. Of the 54 shells, which contained the 

 parasite, one was infected by 7, and two by 4, individuals which were 

 all very young. 



The longest specimen of M. japonica is about 45 mm. long and 

 4 mm. broad when fully extended, and the oesophageal region is broader 

 than the posterior. When contracted, its length is reduced to nearly 

 one-half, and the posterior part of the oesophageal region is slightly 

 concave. The ground color is dark yellow. 



