Anatomy and ultrastructure of the reproductive organs in Dactylopodola typhle (Gastrotricha: Macrodasyida) and their possible functions in sperm transfer

Abstract

Abstract. The reproductive anatomy of gastrotrichs is well known for several species, especially for the marine taxon Macrodasyida. However, there is little information on the reproductive organs and the modes of mating and sperm transfer in putative basal taxa, which is necessary for accurate reconstruction of the ground pattern of the Gastrotricha. We present the first detailed morphological investigation of the reproductive system of a putative basal gastrotrich, Dactylopodola typhle, using transmission and scanning electron microscopy, histology, and microscopic observations of living specimens. Dactylopodola typhle is a hermaphrodite that possesses paired female and male gonads, an unpaired uterus with an outlet channel that we call the cervix, and an additional accessory reproductive organ, the so-called caudal organ. We hypothesize that the hollow, secretory caudal organ serves for picking up autospermatozoa (self-sperm), for spermatophore formation, and finally for transferring the autospermatophore to a mating partner. The allospermatophore (foreign spermatophore) is stored within the uterus where fertilization occurs. We think that the mature and fertilized egg is released through the cervix and the dorsolateral female gonopore, and not by rupture of the body wall. Based on the morphology, we provide a plausible hypothesis for spermatophore formation and transfer in D. typhle. Preliminary phylogenetic considerations indicate that the stem species of Macrodasyida, perhaps that of all Gastrotricha, had paired ovaries and paired testes, an unpaired uterus, and only one accessory reproductive organ.

Architecture of the nervous system in two Dactylopodola species (Gastrotricha, Macrodasyida)

“…On the other hand, Kienecke et al (2008) show in their schematic cross sections a and b of Fig. 2 of the region of the testes in D. typhle, where only one paired longitudinal nerve cord is visible in a ventrolateral position.…”

Unusual spermatozoa and reproductive modalities ofXenodasys eknomios(Gastrotricha: Xenodasyidae)

“…A ''receptaculum seminis'' (i.e. a frontal organ) containing sperm and resembling in location and morphology the frontal organ of X. eknomios has been described in Dendrodasys species (Wilke 1954;Schmidt 1974), and a similar structure was reported for a single, unnamed species in the genus Dactylopodola (Ruppert 1991); for a different interpretation of the reproductive system in Dactylopodola see Kieneke et al (2008). No data are available for Dendropodola as the species was described on a single immature specimen (Hummon et al 1993).…”

Reproductive system of the genus Crasiella (Gastrotricha, Macrodasyida)

“…Cephalodasys and Dolichodasys), oocytes mature in a fronto-caudal direction. The dorsal fusion of the two ovaries in order to form an unpaired uterus has been reported in Dactylopodola typhle (Kieneke et al 2008). A connection made of either a solid cell band or an epithelial duct between the ovary and an external, dorsal pore (mating pore?…”

“…A connection made of either a solid cell band or an epithelial duct between the ovary and an external, dorsal pore (mating pore? ), has only been described in Acanthodasys thrinax and Diplodasys ankeli (Thaumastodermatidae), and Dactylopodola typhle, respectively (Ruppert 1978b;Kieneke et al 2008).…”

“…and different species of Thaumastodermatidae. In addition, hypotheses about these processes have been advanced by Teuchert (1968), Balsamo et al (2002), Kieneke et al (2008) and Guidi et al (2009) based upon microscopical and ultrastructural data on species of other families.…”