Redescription of Fridericia heliota (Annelida, Clitellata: Enchytraeidae), a luminous worm from the Siberian taiga, with a review of bioluminescence in the Oligochaeta

The Siberian enchytraeid Fridericia heliota Zalesskaja, 1990 has so far been known only through a paper in Russian briefly describing its luminescence and the major external and internal morphological features. The present study expands that preliminary description, amending it as regards the chaetal formula, the clitellar pattern, the form of the nephridia and the occurrence of glands at the spermathecal orifices, and providing a more comprehensive taxonomic characterization of the species. More detailed information is also given on its habitat and geographical range as well as on its unusual luminous properties. In F heliota, the production of light is confined to the body wall with a pattern corresponding to that of the epidermal gland cells, although it does not involve discharge of luminous mucus. This contrasts with observations on other enchytraeids and on the oligochaetes in general. Records of luminosity in the Oligochaeta are reviewed with comments.