The classification of land snails of the genus Trishoplita is difficult due to large intraspecific variation in the shell and internal morphology. We studied geographic variation in four subspecies of T. eumenes (mainly T. eumenes cretacea) and T. pallens, using statistical analyses of the shell morphology and character comparisons of the soft body. Overall, three types (Groups A–C) were distinguished in the shell morphology of T. eumenes cretacea. Among them, Groups A and B also had similar characteristics in terms of the branch number of the mucous gland and the shape of the love dart. However, more black spots were present on the mantle of individuals in Groups A and C than in Group B. Based on these characteristics, geographic differentiation of the three groups of T. eumenes cretacea is discussed. The subspecies T. eumeneseumenes and the related species T. pallens share similar morphological characters.
Allozyme variability in the androgenetic freshwater clams Corbicula leana from Japan and the exotic C. fluminea were investigated. A total of 462 individuals of C. leana from 19 localities throughout the distribution range of the species were monomorphic at three allozyme loci as well as in purple inner shell color. Corbicula fluminea from three localities, on the other hand, was variable in shell color; with white, purple, white with purple flash, or deep purple examples. The present results suggest that they may include several clonal lines with different shell colors and allozyme genotypes. We discuss possible diversification of freshwater clams among bisexual species and hermaphroditic clones through clonal capture, genome capture, or ploidy elevation.
We examined the effects of the anesthetic agent MS-222 on glochidial viability in Anodonta japonica, the parasitization rate of the glochidia on the host fish Gymnogobius urotaenia and the metamorphosis rate into juveniles in vitro. Snap frequency of the glochidial valves decreased with an increase in MS-222 concentration. Likewise, parasitization success of the larvae on the gills of G. urotaenia was reduced when the host fish was exposed to an MS-222 solution(150 mg-1L)for five minutes prior to introducing the glochidia to the fish. Metamorphosis success(juveniles/free-living larvae ratio)was reduced by 50% when the host fish was anesthetized with MS-222, though the effect of the anesthetic agent was not detectable statistically. These suggest that glochidial viability and parasitization rate data obtained from previous studies using MS-222 may have contained an artifact. Therefore, future studies on the parasite-host relationship between unionid glochidia and host fishes when MS-222 is used should consider the effect of the anesthetic agent on unionid glochidia.