Development of the genital ducts and spermathecae in the rhyacodrilines Rhyacodrilus coccineus and Monopylephorus rubroniveus (Oligochaeta, Tubificidae)

The male genital duct in Tubificidae consists of a funnel, a vas deferens, an atrium, and, frequently, a copulatory structure. There may also be a dif fuse or compact prostate gland in association with the duct. The morphogene sis of this duct is described for Rhyacodrilus coccineus and Monopylephorus rubroniveus (Rhyacodrilinae). The funnel and vas deferens in both species originate from peritoneal (mesodermal) cells in the posterior septum in the testis segment. The atrium in R. coccineus develops from a primary epiderm al (ectodermal) invagination. A typical atrium is not formed in hi. rubroni veus; the entire duct is of mesodermal origin. In the latter species, a sha llow epidermal invagination occurs, into which both male ducts open, but it bears resemblance to a copulatory structure, which usually forms from a se condary invagination, rather than to a proper atrium. We therefore conclude that M. rubroniveus lacks an atrium. The copulatory structure is termed th e male bursa. Both species have diffuse prostate glands that differentiate from peritoneal (mesodermal) cells surrounding the male duct. In R. coccine us the cells cover the atrium, whereas in M. rubroniveus they cover only a part of the vas deferens. The development of the spermathecae and female du cts is also examined. The spermatheca is of ectodermal origin in both studi ed species, i.e., it forms as an invagination of the epidermis. The female duct develops from peritoneal (mesodermal) cells in the posterior septum of the ovary segment. However, in M. rubroniveus the first sign of the duct d isappears and a proper duct never develops. (C) 1999 Wiley-Liss, Inc.