1959 年 24 巻 4 号 p. 487-497
1. The chromosomes of six Melaniid snails have been studied. The chromosome numbers of the various forms are as follows.
Melania crenulata _??_ 2n=34+X=35
Paludomus tanschaurica _??_ 2n=36+XY=38
Melanoides tuberculatus (diploid race) _??_ 2n=32
Melanoides tuberculatus (polyploid race) _??_ and_??_ 90-94
Melanoides lineatus _??_ and _??_ .............71-73
Melanoides scabra _??_ ..................76-78
2. The chromosomes of all the Melaniids studied are metacentric and in this respect their chromosome complements are similar.
3. All the Melanoides except the diploid race of M. tuberculatus are high polyploids and these add to the only one instance of polyploidy so far known in Molluscs.
4. The co-existence of parthenogenesis and polyploidy may account for the numerous forms of Melanoides, their variability, wide distribution and consequent taxonomic difficulty. In view of the prevailing confusion in identification and nomenclature of the Melaniids in general, a cytotaxonomical approach seems imperative. An indication of this is provided by the two races of M. tuberculatus.
5. The two cytologically distinct races of M. tuberculatus though not markedly different with respect to size and external morphology do show ecological physiological and biochemical differences. Polyploidy seems to confer hardiness and selective advantage.