Spermiogenesis and the spermatozoon were studied in the digenean Mesocoelium monas Rudolphi, 1819 (from the toad Bufo sp. in Gabon). An ultrastructural study revealed that spermiogenesis follows the usual pattern found in digeneans, i.e. proximo-distal fusion of axonemes with a median cytoplasmic process followed by elongation. The spermatozoon has two fully incorporated axonemes with the 9 +“1” trepaxonematan pattem. Indirect immunofluorescence localization of tubulin and fluorescent labelling of the nucleus were used to obtain additional information on the structure of the spermatozoon. It was thus shown that one of the axonemes is slightly shorter than the other (190 versus 220 pm) and that the filiform nucleus (65 pm in length) is located at the distal extremity of the spermatozoon (220 pm in length). Various monoclonal and polyclonal antibodies, specific to alpha, beta, acetylated-alpha, or general tubulin, were used and produced similar labelling.
Subepidermal glands of the body of Troglocaridicola sp. (from the cavemicolous shrimp Troglocaris sp. in eastern Italy) were observed by transmission electron microscopy. The reservoir and duct of the glands arc lined with longitudinal microlubulcs. Membrane-bound granules inside the gland show a distinctive pattern: they contain fibres, 18 nm in diameter, regularly arranged in bundles with a 5 nm space between libres. From a survey of the available literature on glands of Platyhelminthes, it is concluded that this structure is known only in this species. Glands with regularly arranged 18 nm fibres, if characteristic for the Scutariellidae, could be considered an autapomorphy of this family, distinguishing it from other members of the Temnocephalida.
While the majority of polyopisthocotylean monogeneans feed on blood, some polystomatids infecting chelonians do not. This study examined the gastrodermis of two polystomatids, one - Neopolystoma spratti Pichelin, 1995 - from the conjunctival sac of a chelonian and the other - Concinnocotyla australensis (Reichenbach-Klinke, 1966) - from the oral cavity, gill arches and primary gill lamellae of a fish, and also found no evidence of blood feeding. However, the gastrodermal architecture in both species basically resembles that found in blood feeding polyopisthocotyleans, with alternation of lamellated digestive cells and an intervening syncytium. In C. australensis, oesophageal secretion appeared to be responsible for initial extracellular digestion and this was followed by pinocytotic uptake of partly degraded material in pits between the numerous apical lamellae of digestive cells. Posterior dorsolateral gut pockets unique to C. australensis were shown to be blind sacs separated from the external environment by a narrow cytoplasmic bridge, composed of a thin layer of tegument apposed to a thin layer of pocket syncytial epithelium. The pockets are lined with greatly folded syncytium and set in a “capsule” of tissue in which numerous pro-tonephridial flame cells are embedded. It is suggested that the pockets have an osmoregulatory function related to the particular environment and evolutionary history of the host, the primitive lung fish (Dipnoi) Neoceratodus forsteri (Krefft, 1870).