Ultrastructure of the neodermal sclerites of Gyrocotyle urna Grube and Wagener, 1852 (Gyrocotylidea, Cestoda)

Abstract

Body sclerites of Gyrocotyle urna Grube and Wagener, 1852, parasites of Chimaera monstrosa L., were studied by transmission electron microscopy. Each sclerite consists of ten to 15 concentric layers varying in electron density and thickness. The sclerites insert in pockets whose epithelia are continuous with the body neodermis but are 14 times thinner. The pocket neodermis bears surface projections with an inner electron-dense cylinder and a small electron-dense cap at their tip. It is surrounded by a well-elaborated basement lamina and bundles of musculature; the perikarya of this part of the neodermis lie underneath the basement membrane. The luminal plasma membrane of the pockets is covered by a coat originating from vesicles and dense bodies most probably discharged from the pocket neodermis, supporting the assumption that the deposition of this material builds up the sclerites. Therefore, sclerites are derivatives of the neodermis. With regard to their ultrastructure, sclerites resemble the calcareous corpuscles of other cestode taxa. They represent a useful phylogenetic character and are an autapomorphy of the Gyrocotylidea.

Ultrastructure of the anterior organ and posterior funnel-shaped canal of Gyrocotyle urna Wagener, 1852 (Cestoda: Gyrocotylidea)

“…The aim of the present study is to provide data on the ultrastructure of the anterior organ at the anterior end and the funnel-shaped canal of the posterior attachment organ of Gyrocotyle urna Wagener, 1852. This account is a follow-up of our previous ultrastructural studies on these enigmatic flatworms (Poddubnaya et al 2006, 2008, 2009, Xylander and Poddubnaya 2009, helping to obtain additional ultrastructural characters suitable for the reconstruction of the evolutionary history of basal tapeworms and their functional morphology.…”

“…The ultrastructural investigations on G. urna have highlighted some ultrastructural characters that may be useful for unravelling the evolutionary history of the Gyrocotylidea and their phylogenetic relations with other parasitic flatworms (Neodermata). These characters of potential phylogenetic importance include: (i) capilliform filitriches on the body surface of gyrocotylideans and 'true' tapeworms (Eucestoda); (ii) laminate nature of gyrocotylidean neodermal sclerites that somewhat resembe calcareous corpuscles of eucestodes; (iii) similarity between secretory glands of the posterior rosette of G. urna and those in the anterior attachment glands of monogeneans; (iv) the structural arrangement of the protonephridial terminal organ in gyrocotylideans and some monogeneans; (v) apical structures of protonephridial canal walls of gyrocotylideans and spathebothriidean tapeworms; (vi) cellular nature of protonephridial ducts in gyrocotylideans, monogeneans and trematodes; (vii) the similarity in the degree of division of the ovary and arrangement and structure of associated ducts in G. urna and the early derived monogenean genus Chimaericola Brinkmann, 1942; (viii) discriminatory characters of the cytoarchitecture of the vitelline follicles of gyrocotylideans and eucestodes; (ix) unique uterine ultrastructural pattern with the cellular nature of the uterine tube of gyrocotylideans, monogeneans and trematodes; (x) uterine glands of the middle portion of the uterine tube in gyrocotylideans and spathebothriideans; and (xi) spermatozoon with mitochondria in gyrocotylideans, monogeneans and trematodes (Xylander 2001, Poddubnaya et al 2006, 2008, 2009, Xylander and Poddubnaya 2009.…”