A taxonomic study of Enchytraeus japonensis (Enchytraeidae, Oligochaeta): Morphological and biochemical comparisons with E-bigeminus

Abstract

Enchytraeus japonensis, a terrestrial enchytraeid, reproduces asexually by fragmentation and subsequent regeneration. Because of its extreme ability to regenerate, the species has recently been proposed as a new experimental material for regeneration study, and a method has been developed for inducing sexual reproduction in the laboratory. The inducibility of sexual reproduction allowed us to perform, for the first time, a taxonomical analysis of E. japonensis based on the morphology of the genital organs, and to compare it with the morphology of the highly similar E. bigeminus, another fragmenting enchytraeid. Comparisons between the two species were also made for general protein patterns and isozyme patterns of seven enzymes using PAGE-IEF. The morphological investigation revealed that the two species are discriminable by only one character; glandular bodies associated with the male copulatory organs that are present in E. bigeminus but absent in E. japonensis. In contrast to this morphological similarity, protein patterns were highly divergent between the two species; 29 (55%) out of 53 distinguishable bands of general proteins and 25 (86%) out of 29 isozymes of the enzymes examined (EST, MDH, PGM, GPI, LDH, ME, and HE) were species-specific. These results suggest that Enchytraeus japonensis and E. bigeminus are closely related but different species.