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 (Tubi®cidae): Limnodriloides rubicundus; Tectidrilus bori; Thalassodrilides ineri. All tubi®cids 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 ®bres. 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 classi®cation 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.

Development of the genital ducts in Telmatodrilinae (Tubificidae, Clitellata)

“…The plate will differentiate to form the male funnel and vas deferens. This general description of the development of the vas deferens and funnel has previously been shown for many microdrile oligochaetes (Vejdovsky, 1884; Gatenby, 1916;Mehra, 1924Mehra, , 1925Hrabe, 1939;Gustavsson andErséus, 1997, 1999;Gustavsson, 2002), and only the location varies.…”

“…In other tubificid species studied (e.g., Clitellio arenarius, Tubificoides benedii, Limnodriloides rubicundus, Thalassodrilides ineri, and Tectidrilus bori), the funnel plate is composed of a thick mass of small cells instead of a layer, and an organization into a distinct cell layer does not occur until later in development (Gustavsson and Erséus, 1997;Gustavsson, 2002). This is similar to funnel development in Alexandrovia onegensis, where the early plate is composed of small cells and not organized into any distinct layer.…”

“…However, the development of the atrium in T. tubifex has been studied several times, and whereas Mehra came to the same conclusion as Gatenby (1916), both Vejdovsky (1884) and Hrabe (1939) claimed that the atrium in T. tubifex has an ectodermal origin. All other tubificids studied have been reported to have an atrium of ectodermal origin (Vejdovsky, 1884;Gatenby, 1916;Mehra, 1925;Hrabe, 1939;Gustavsson andErséus, 1997, 1999;Gustavsson, 2002), with the exception of Monopylephorus rubroniveus. The development of the genital ducts in this species was first commented on by Cook (1970), who indicated a mesodermal origin for the atrium and prostate glands.…”

“…Here the funnel begins as a single layer of columnar cells in close contact with the anterior side of septum 10/11, that is, the plate is organized into a distinct layer from the beginning. This description also applies to Heterochaeta costata (Tubificinae) and Rhyacodrilus coccineus (Rhyacodrilinae), both of which have an early organized funnel plate consisting of a single layer of high columnar cells (Gustavsson andErséus, 1997, 1999).…”

“…Thus, close scrutiny of morphological features is necessary before forming primary hypotheses of homology. One way to improve primary hypotheses is to study the development of the genital ducts in representatives of the different subfamilies within Tubificidae, and several species from Tubificinae, Naidinae, Rhyacodrilinae, and Limnodriloidinae have been studied (reviewed in Gustavsson andErséus, 1997, 1999).…”