Ultrastructure of Epidermis and Sperm of the Turbellarian Syndisyrinx-Punicea (Hickman, 1956) (Rhabdocoela, Umagillidae)

Abstract

Syndisyrinx punicea has an epidermis with intraepidermal nuclei, a thick basal lamina, and microvilli containing an array of densely packed filaments and, in the widened tips, an electron-dense cap. The epidermal cilia posess a widened cytoplasmic portion close to the base and vertical and horizontal cross-striated rootlets; the latter are anchored in the adjacent matrix by means of transverse bars. Basal bodies have a distinct spike opposite the horizontal rootlet. In the tips of epidermal cilia, one of the microtubules disappears first in doublets 7-9 and 1, and gradually all peripheral doublets disappear; there is no electron-dense rod along the central microtubules, but cilia have a terminal electron-dense cap. Spermatozoa have two flagella, much shorter than the sperm (and not incorporated in it); axonemes are of the 9+'1' type; an elongate nucleus, numerous small mitochondria and electron-dense bodies are surrounded by a single peripheral row of microtubules in the thicker parts of the sperm, in the thinner parts (apparently close to the ends) microtubules are also found in the interior; some electron- dense bodies were also seen free between sperm, indicating their secretory function. Ultrastructural evidence does not support the view that Umagillidae (as well as Temnocephalida) are particularly closely related to the Neodermata, the major parasitic groups of Platyhelminthes.