Fragmenting oligochaete Enchytraeus japonensis: a new material for regeneration study.

Enchytraeus japonensis, a recently described terrestrial oligochaete, reproduces asexually by fragmentation and subsequent regeneration. Taking notice of its high potential as a new material for regeneration study, detailed studies were undertaken on the regeneration and reproduction of E. japonensis. The full-grown body divided into 6-13 fragments that regenerated into complete individuals in 4 days, grew to full length in 10 days, and then fragmented again. Regeneration of the head and tail was epimorphic, involving blastema formation, while old segments in the regenerating fragment morphallactically transformed into the appropriate segments to retain the proper body proportions, which could be visualized by histochemistry for alkaline phosphatase. Artificially cut fragments regenerated either normally or into dicephalic monsters with biaxial heads depending on the conditions. Fragmentation could be induced by decapitation, and sexual reproduction was also found inducible in the laboratory. These findings, together with its simple metameric morphology and ease of culture and handling, suggest that E. japonensis is an excellent material for studying animal regeneration.