Ultrastructural analysis revealed that the spermatozoon of Discocotyle sagittata (Leuckart, 1842) is composed of two parallel axonemes, mitochondrion, nucleus and cortical microtubules. The nucleus, which occupies a central/distal position and has an unusual crescent-shaped profile, is slightly shorter than the mitochondrial rod. The two axonemes, which are of unequal length, and the cortical microtubules (up to 68 forming a continuous ring in the principal region) extend almost the entire length of the spermatozoon. A fold of the plasma membrane creates a unilateral flange or undulating membrane. Epifluorescence microscopy indicated that spermatogenesis gives rise to clusters of 64 spermatids connected to a common cytophore. Spermiogenesis and the structure of the filiform sperm of D. sagittata conform to the typical polyopisthocotylean pattern.
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.
Using scanning and transmission electron microscopy, ultrastructure of the anterior organ and posterior funnel-shaped canal of Gyrocotyle urna Wagener, 1852 (Cestoda: Gyrocotylidea) from ratfish, Chimaera monstrosa (Holocephali), was studied for the first time. The proper anterior organ is localised at a short distance (about 170 µm) from an apical pore surrounded by a receptor field, whereas its distal end is marked by a muscular sphincter. The tegumental surface of this organ is covered with short filitriches of irregular length; large area of muscle layers traverse beneath the tegumental layer. The funnel-shaped canal of G. urna (2.5-3.0 mm long) is a specialised, muscular part of the posterior attachment organ; it opens on the rounded elevation on the dorsal body surface. The tegumental layer bears conical sclerite-like structures (up to 1.5 µm long). It produces electron-dense bodies that are transported into a canal lumen and surrounded thick muscle area mixed with numerous nerve fibres. The present ultrastructural study of G. urna indicates that gyrocotylideans share some ultrastructural characters of the anterior organ with spathebothriidean cestodes with a single anterior attachment sucker-like organ. In contrast, the unique posterior rosette attachment organ with funnel-shaped canal of the Gyrocotylidea resembles the haptor of polyopisthocotylean monogeneans in its position at the posterior end of the body and presumed origin. The above-mentioned features add more clarity to support the basal position of the Gyrocotylidea Poche, 1926 among cestodes. In addition, they also indicate a possible relationship of gyrocotylidean ancestors with monogeneans., Larisa G. Poddubnaya, Roman Kuchta, Glenn A. Bristow, Tomáš Scholz., and Obsahuje bibliografii
In the apical glandular region of the adult Proteocephalus torulosus (Batsch, 1786), two types of eccrine gland cells are present. The first type of unicellular gland produces large electron-dense granules of various sizes. The second type contains small electron-dense granules. Most cells form glands with large granules; glands with small granules are infrequent. The secretion of both types of gland cells is concentrated in the apical parts of the cyton and in the ducts opening to the exterior. On the scolex of P. torulosus, there are regional structural differences of the microthrix border. The apical glandular region bears filamentous microtriches only. On the remaining frontal part, surrounding the glandular region, there are blade-like and filamentous microtriches. The lateral parts of the scolex and suckers bear blade-like microtriches. Possible functions of both types of gland cells and different parts of the scolex microthrix border are discussed. The unique structure of the frontal part of the scolex of P. torulosus and its differences from Proteocephalus macrocephalus, P. longicollis and P. percae correlate well with the putative basal phylogenetic position of P. torulosus among European species of Proteocephalus.
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).
The forebody and foregut of Crepidostomum metoecus Braun, 1900 are invested with a tegument bearing regularly arranged surface tubercles comparable with the aspidogastrean surface structures. The tegument of the ventrolateral lobes and of the prepharynx is penetrated by ducts of eccrine gland cells. The frontal and prepharyngeal gland cells, localised in the parenchyma, discharge electron-dense granules. Their ducts are lined by peripheral microtubules and fixed to the tegument plasmalemma by a septate junction. The functional roles of these glands are discussed.
The frontal gland as a sac-like organ in Prorhinotermes simplex is present only in presoldiers, soldiers, and imagoes, but exists also in nymph-soldier intercastes. The secretory epithelium consists of a single type of secretory cells adhering directly to the cuticular intima. Secretory vacuoles originate in electron dense vesicles, which are transformed into large electron lucent vacuoles. Intermediate vacuoles frequently contain lipid droplets. The frontal gland cells in presoldiers reveal modifications connected with the production of a new cuticle; the new cuticle is thin and compact, whereas the old one is thick, porous, and wrinkled. None of these cuticles is present in soldiers (sic!). In soldiers, the cuticular intima is of endocuticular origin and is formed by dispersed dense material; the apical parts of secretory cells are formed by numerous irregular finger-like projections, true microvilli are completely lacking. In imagoes, the cuticle is composed of an epicuticle, a layer of epicuticular filaments, and one more basal layer; sexual differences were not observed. In nymph-soldier intercastes, the structure of the gland differs in the head and in the metathorax; the head part of the gland resembles the imaginal gland whereas the thoracic part resembles more that of the soldier; the development of secretory vacuoles stops at the stage of presence of lipid droplets. E-1-nitropentadecene was found in the highest amount in soldiers (comparable to P. inopinatus soldiers), in moderate amount in imagoes, and it is missing in both presoldiers and intercastes.
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).
An ultrastructural study of the ovarian follicles and their associated oviducts of the cestode Gyrocotyle urna Grube et Wagener, 1852, a parasite from the spiral valve of the rabbit fish, Chimaera monstrosa L., was undertaken. Each follicle gives rise to follicular oviduct, which opens into one of the five collecting ducts, through which pass mature oocytes. These collecting ducts open into an ovarian receptacle which, in turn, opens via a muscular sphincter (the oocapt) to the main oviduct. The maturation of oocytes surrounded by the syncytial interstitial cells within the ovarian follicles of G. urna follows a pattern similar to that in Eucestoda. The ooplasm of mature oocytes contain lipid droplets (2.0 × 1.8 µm) and cortical granules (0.26 × 0.19 µm). The cytoplasm of primary and secondary oocytes contains centrioles, indicating the presence of the so-called ''centriole cycle'' during oocyte divisions. A morphological variation between different oviducts was observed. The luminal surface of the follicular and the collecting oviducts is smooth. The zones of the septate junctions are present within the distal portion of the net-like epithelial wall of the collecting ducts close to the ovarian receptacle. The syncytial epithelial lining of the ovarian receptacle, oocapt and main oviduct is covered with lamellae and cilia. Cortical granules secreted from mature oocytes occur freely within the lumen of the main oviduct that functions as a fertilisation canal. A division of the ovary into separated parts with their own collecting ducts as that typical of Gyrocotyle has been observed in neodermates, basal monogenean family Chimaericolidae, and Neoophora (some Proseriata and Fecampiidae). Ultrastructural data thus reveal several unique morphological characteristics of gyrocotylideans, the most basal taxon of tapeworms (Cestoda).
Ultrastructure of the primitive epithelium of Echinostoma revolutum (Digenea: Echinostomatidae) cercaria was studied. The germinal balls and developing cercariae are covered with the primitive epithelium in daughter rediae. When the definitive tegument of the cercaria is differentiated, the primitive epithelium degenerates. The last remnants of the primitive epithelium in a cercaria can be detected at the stage when the lateral gland cells have released their secretion into the definitive tegument.