Spermiogenesis in Phyllobothrium lactuca Beneden, 1850 begins with the formation of a differentiation zone bordered by cortical microtubules and containing a nucleus and two ccntrioles separated by an intercentriolar body and disposed one in the prolongation of the other. Later, formation of flagellar buds, striated roots and a median cytoplasmic extension takes place. Each centriole gives rise to a flagellimi that rotates and fuses with the median cytoplasmic extension. At this stage, arched membranes appear at the front of the differentiation zone. The nucleus elongates, becomes filiform and migrates between the striated roots into the spermatid. After the migration of the nucleus, the old spermatid separates from the residual cytoplasm by strangulation of the ring of arched membranes. Absence of striated roots, right at the beginning of spermiogenesis has never been described before in the Tctraphyllidea. Likewise, centrioles made up of doublets of microtubules and spermatids with two axonemes have never been reported before during spermiogenesis of a Phyllobothriidae. In this work we show, for the first time, the existence in cestodes of thick-walled microtubulcs surrounded by a layer of electron-dense material. In addition, we describe, for the first time, the existence of an accumulation of electron-dense granules around striated roots and an hour-glass-shaped constriction at the anterior extremity of a median cytoplasmic extension in a platyhelminth.
The ‘buccal complex’ of Pricea multae Chauhan, 1945 consists of two buccal suckers, the pharynx, a putative taste organ and the mouth cavity. The two suckers are dorsal to the mouth cavity, and the pharynx posterior to them. The septum in each sucker consists of connective tissue containing muscle filaments, lined by tegument with short irregular microvilli. The mouth cavity and the lumen of the suckers are lined by tegument with short irregular lamellae and by tegument with long bulbous, interconnected lamellae, separated from each other and from the body surface tegument by septate junctions. A ventral extension of the mouth cavity is also lined by tegument with short irregular lamellae. An anterior ‘taste organ’ is lined by ‘normal’ (body) tegument and tegument with short irregular lamellae. Glandular ducts open into it, and it contains many small uni-ciliate and multiciliate receptors, as well as two receptor complexes each consisting of a large non-ciliate receptor surrounded by small and large uniciliate receptors, with multiciliate receptors closeby. The four types of receptors are described in detail. The anterior part of the pharyngeal lumen is lined by an epithelium with dense surface lamellae and is penetrated by non-ciliate receptors. Attention is drawn to significant differences between the buccal complexes of the polyopisthocotylean monogeneans Pricea multae (Gastrocotylidae), Gotocotyla secunda (Tripartii, 1956) (Gastrocotylidae), Pulylabroides australis (Murray, 1931) (Microcotylidae), Zeuxapia serialae (Meserve, 1938) (Axinidae) and Diclidophora merlangi (Kuhn, 1832) (Diclidophoridae).
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).
The ultrastructure of the scolex tegument, bothridial pits (“ciliated pits) and rhyncheal system of Otobothrium mugilis Hiscock, 1954 is described from plerocerci collected from the teleosts Arius graeffei Kncr ct Steindachner and Mugil cephalus Linnaeus. Scanning electron microscopy revealed that filamentous microtriches with shortened caps are abundant across the entire surface of the tegument. Palmate microtriches are dominant on the bothridia and their margins. The surfaces of bothridial pits were covered with large bifid microtrichcs. The bothridial pits arc strongly muscularised invaginations of the tegument. Nervous tissues were not observed within the pits and it is probable that these structures function as accessory attachment structures. The wall of each tentacle sheath consists of one to three bands of fibrils, lined internally by a thin cytoplasmic layer. The tentacular walls are cellular, containing myofilaments. The fibrils of the tentacular walls are arranged into discrete blocks of parallel fibrils and appear to be intracellular. Tentacular walls are lined externally by a modified membrane with an external glycocalyx. Tentacular hooks arc solid, bound externally by a membrane. The body of the hook contains numerous longitudinal canaliculi and an elcctron-opaquc medulla lies at the centre of the hook.