The development of the genital ducts in Limnodriloidinae (Tubificidae, Clitellata)

Abstract

The development of the male duct and spermatheca is studied in three species of the marine Limnodriloidinae (Tubificidae): Limnodriloides rubicundus; Tectidrilus bori; Thalassodrilides ineri. All tubificids are hermaphroditic with paired male ducts, female ducts and, as a rule, spermathecae. The male duct comprises a funnel, followed by a vas deferens, an atrium and, frequently, a copulatory structure. There may also be a diffuse or compact prostate gland in association with the male duct. In the three species studied, the funnel and vas deferens originate from peritoneal (mesodermal) cells in the posterior septa of the testes segment. The atrium develops from an invagination of the epidermis (ectoderm). The vas deferens and atrium subsequently connect to each other, and a continuous duct from the testes segment to the exterior is formed. The prostate gland originates from large peritoneal cells occurring in a delimited area on the outer surface of the atrium; other small peritoneal cells surrounding the whole atrium give rise to muscle fibres. The spermatheca develops from an invagination of the epidermis, and is thus of ectodermal origin. The morphology and position of the genital ducts have been and are important for the classification of the oligochaetes. However, different parts of the male duct have been named without regard to whether they are homologous or not. One way to establish stronger primary hypotheses of homology is to study the detailed morphology and/or the development of the genital ducts.