Histology and Ultrastructure of the Body Wall in the Phoronid Phoronopsis harmeri

The histology and ultrastructure of the body wall in Phoronopsis harmeriwere studied using light microscopy and TEM. The ectoderm epithelium of tentacles, anterior body region, and ampulla consists of monociliary cells. Gram-negative bacteria were found between microvilli, in the protocuticle of the anterior region, and in the ampulla. The epithelium of the posterior body region lacks both monociliary cells and bacteria. The bundles of nerve fibers run between the layer of epithelial cells and basal membrane. The musculature of the body wall comprises circular and longitudinal muscles. The circular muscle fibers are applied to the basal membrane and constitute a solid layer extending almost throughout the length of the body. This pattern is broken in the posterior body region, where there is no solid layer of circular musculature, and the latter is arranged in isolated muscle bands. In the ampullar (terminal) body region, the inversion of circular and longitudinal muscle layers takes place, so that the latter appears to be pressed against the basal membrane. The apical surfaces of longitudinal muscle cells bear cytoplasmic processes; some of the cells have a flagellum. The basal portion of the longitudinal muscle cells forms a cytoplasmic process containing bundles of tonofilaments. The processes of all cells making up the muscle bands are interwoven and anchored to the basal membrane.     

The ultrastructure of the marine gastrotrichTurbanella cornuta Remane (Macrodasyoidea) and its functional and phylogenetical importance

Summary The organization of marine gastrotrichs (Macrodasyoidea) is reviewed by ultrastructural analysis of one representative,Turbanella cornuta Remane, and the fine structure of tissues and cells is described. Turbanella cornuta has a mono-layeredcellular epidermis rich withsensory hairs, epidermal bodies, isolatedepidermal glands, glandular adhesive organs belonging to a duo-gland type, andventral ciliated epidermal cells of the multiciliated type. The voluminous neuropil of thebrain consists of a circular commissure which sends out four anterior and posterior longitudinal headnerves. The posterior ones unite on each side to one single longitudinal nerve of the periphery which is occupied with single peripheral neurons and has thin commissures that make it anorthogon. The position and the structure of the neurons indicate their sensitive, associative, motoric, and neurosecretory functions. The different forms of synapses give first hints to neuronal connections within gastrotrichs. There is a big cellularglia around the brain commissure and a small cellular glia within the brain neurons. In between the cross-striated muscle fibrils of thepharyngeal wall there are also nerves and sensory hairs.TheY-organ lies in the interior of the lateral body cavities, which are delimited by an outer musculature of the body wall and an inner musculature of the intestinal tract. In the pharyngeal region, theY-organ fills the body cavities completely and, in the intestinal region, it covers thegonads, which also lie in the lateral body cavities, dorsally. The testicles lie separately in front of the paired ovaries. Single states of oogenesis could be identified as oogonia, and young and old oocytes. There is a paired gland organ in front of the dorsomedian ovary which may produce a mucous cover for the egg.Theintestinal tract is adapted to mechanical stress by a myoepithelium in the pharyngeal region, by various interdigitations, and by narrow intercellular gaps with hemidesmosomal adhesions to the basement membrane. The majority of the resorbing intestinal cells have a high seam of microvilli and contain various numbers of lysosomes. In addition, there are some secerning cells without microvilli, but with a centrically arranged ER and with big secretion granules in the dorsomedian sector.The ultrastructure affirms a close correlation between the conditions of life in the interstitium and structural adaptations, such as may be observed in single structures of the body wall, the y-organ, the intestinal tract and, in some respect, even in the nervous system and in the formerly researched musculature and spermatohistogenesis. On the other hand, for the construction of the glandular adhesive organs, the nervous system, and the formerly investigated body cavities, a phylogenetical relevance is discussed. Thereafter, gastrotrichs have more primitive characters than the closely related nematodes.Abbreviations a sensory hair cells - am ampoule - at outleading tube - b basement membrane - bb basal body - c cilium - cr rootlet of the cilium - cu cuticle - cw cell wall - d d-cells of the brain - de desmosomes - e e-cells of the brain - eb epidermal bodies - ee ripe egg in the dorsomedian ovary - ep epidermis - er endoplasmatic reticulum - ev ventral ciliated epidermal cells - f f-cells of the brain - fr fibrillar structure - g gland cell - ge germ epithelium - gl₍₁₊₂₎ small and big cellular glia of the br - go Golgi-apparatus - gp genital pore - h h-cells of the brain - hf lateral adhesive tubules - hfp posterior adhesive tubules - i intestine - il intestinal lumen - 1 lumen of the organ - li lipid granules - ly lysosomes - m mitochondrium - mb multivesicular body - mc circular musculature - mi microvilli - ml longitudinal musculature - mo mouth opening - mt microtubules - mpl longitudinal muscle fibers of the pharyngeal wall - mpr radial muscle fibers of the pharyngeal wall - n nucleus - nb brain neurons - nc brain commissure - nf nerve fibers - nl lateral headnerve - nm nuclear membrane - nn nucleolus - nv ventrolateral headnerve - nz peripheric neuron - ncp peripheric nerve commissure - nvp longitudinal peripheric nerve - o lateral ovary - oc oocyte - oo oogonium - ow wall cells of the ovary - p secretory pore - ph pharynx - po palpar organ - phb pharyngeal bulbs - phl pharyngeal lumen - phn nerve plexus of the pharynx wall - sa anterior sense organ - sg secretory granules - sh sensory hair cell - sp posterior sense organ - st supporting stick - su supporting cell - sv synaptic vesicles - sy synaptic gap - t testicles - tl testicular lumen - tw wall cells of the testicles and the vas deferens - v ventral - va vacuoles - vd vas deferens - vs vesicles - y y-organ - yc anterior commissure of the y-organ - z yolk granules     

Myology of the Feeding Apparatus of Myrmecophagid Anteaters (Xenarthra: Myrmecophagidae)

The musculoskeletal feeding apparatus of anteaters in the family Myrmecophagidae (Eutheria: Xenarthra) is described, compared among the three extant genera (Tamandua, Myrmecophaga, Cyclopes), and interpreted in a phylogenetic framework. Character polarities are assessed with reference to other xenarthrans, eutherians, and didelphid marsupials. Xenarthrans are widely regarded as basal eutherians, and this is reflected in the apparent retention of plesiomorphic character states in jaw and pharyngeal musculature. Jaw closing muscles are architecturally simple, the stylohyoideus is absent, the stylopharyngeus is robust and architecturally complex, and the superior pharyngeal constrictor is weak. At the same time, the highly specialized trophic ecology of myrmecophagids is reflected in derived features of the jaw, tongue, and palatal musculature. The sternomandibularis is present, the tongue is largely composed of a sternog-lossus with no attachments to the hyoid apparatus, other glossus muscles are modified and do not enter the tongue, and the mylohyoideus and stylopharyngeus contribute to the soft palate, while other palatal muscles vary among the myrmecophagid genera. Feeding apparatus mycology provides further support for myrmecophagid monophyly. Documentation of the morphological transformations that lead to the myrmecophagid condition is hampered by incomplete data on feeding apparatus structure in nonmyrmecophagid xenarthrans (sloths and armadillos) but a tentative character mapping onto an independently derived phylogeny is offered.     

Fine structure of the coelomic epithelium of Sagitta elegans (Chaetognatha)

Summary The coelomic space in the trunk of the arrow worm Sagitta elegans is lined by a thin epithelium, which may be termed coelomic epithelium. The visceral part of this epithelium is composed of flat cells characterized by thin and thick myofilaments, which constitute the circular musculature of the gut. In addition mitochondria, rough ER, and smooth walled cisterns, as well as vesicular and granular inclusions occur; the apical and basal plasma membranes exhibit no particular specializations. The parietal epithelium is exceedingly thin and covers the muscle cells of the body wall. In the lateral fields columnar ciliated cells are to be found which are rich in rough ER cisterns and which apparently are also coelomic epithelial cells.     

Anatomy and Ultrastructure of Ventral Pharyngeal Organs and their Phylogenetic Importance in Polychaeta (Annelida). IV. The Pharynx and Jaws of the Dorvilleidae

An anatomical and ultrastructural investigation of the ventral pharyngeal organ, jaws and replacement of jaws was carried out in Ophryotrocha gracilis and Protodorvillea kefersteini (Dorvilleidae). The pharynx exhibits the following features: jaw apparatus present, consisting of paired mandibles and rows of maxillary plates, the latter are fused to form a single piece; cuticular jaws electron-dense, in P. kefersteini with collagen fibres; muscle bulbus solid, composed of muscle cells only; parallel running myofilaments, centrally located mitochondria and nuclei, bulbus epithelium containing the mandibles and gland cells, maxillary plates lying on folds corresponding to a tongue-like organ, connected with mandibles by longitudinal investing muscles; numerous gland cells not united to distinct salivary glands. Development of jaw replacements occurs in epithelial cavities beside the functional maxillae. Shape of maxillary plates is preformed by microvilli carrying cell processes. Maxilloblasts change their shape during the development. Synapomorphic structures occurring in ventral pharyngeal organs of other species outside the Eunicea are not present and even the closely related Dinophilidae exhibit a completely different pharyngeal organ. Therefore, convergent evolution of these organs is the most probable explanation. These findings do not agree with the hypothesis of the homology of the ventral pharyngeal organs in the Polychaeta.     

Histological study of odontogenesis in the pharyngeal jaws of Trachinotus teraia (Cuvier et valenciennes, 1832) (Osteichthyes,Teleostei, Carangidae)

A histomorphological study of the development of the pharyngeal jaws in the Carangid fish Trachinotus teraia shows that they transform progressively from tiny organs with sharp superficial teeth, to thick ones with rounded teeth embedded in bony tissue. The morphological transformations take place simultaneously with a shift to a diet based on molluscs. Though odontogenesis takes place deep in the pharyngeal jaws, at all developmental stages, pharyngeal epithelium participates to the formation of teeth. Long epithelial strands penetrate in the depth of the bony jaw and here induce differentiation of “bell organs.” As the young teeth migrate passively toward the occlusal surface, while the jaw grows, the pharyngeal jaws of Trachinotus teraia almost behave like the “coalesced” teeth of the Tetraodontidae with respect to the morphogenetic processes of their growth. The developmental phenotypic plasticity of the pharyngeal jaws of Trachinotus teraia then may be compared to that of various mollusicivore cichlids. © 1994 Wiley-Liss, Inc.     

The Ultrastructure of the Proboscis in Psammorhynchus tubulipenis Karling, 1964 and Cytocystis clitellatus Karling, 1953 (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in two species of free-living Platyhelminthes, Psammorhynchus tubulipenis and Cytocystis clitellatus is very alike but differs from previously described species. Both sheath and cone epithelium are composed of two circumferential belts. Only the basal cone epithelium is syncytial, while no nuclei were found in the distal belt of the sheath epithelium. The sheath epithelium is characterized by numerous infoldings of the basal plasma membrane. The nuclei present in the bulb belong to the proximal belt of the sheath epithelium and the apical cone epithelium. Nuclei of the basal cone epithelium are located insunk behind the proboscis bulb. The insunk cell parts pierce the septum of the bulb laterally near the proximal end. Different types of gland necks and sensory cells pierce the epithelia. Associated with the distal belt of the sheath epithelium, two sensory organs are found, containing multiciliary receptors with modified axonemata. Differences in organization of the proboscis musculature are described and compared with the organization in other species. The systematic position of both species is discussed in the light of the new findings.     

Anatomy and ultrastructure of the proboscis in Mesorhynchus terminostylis (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in Mesorhynchus terminostylis is distinctly different from that in other members of the Polycystididae in which it is currently classified. The sheath epithelium is formed by three belts, all with intra-epithelial nuclei. The apical belt of the bipartite cone epithelium has a single intrabulbar nucleus, and the basal belt possesses five insunk nucleiferous cell parts behind the bulb. Six types of glands surface through the epithelia; the three types emerging through the cone epithelium can be homologized with those described for Polycistis naegelii. Only uniciliary receptors are found in the epithelium. The musculature in the bulb has a very loose appearance, and the bulbar septum appears to be a bipartite basement membrane. The septum can be considered the basement membrane of the cone epithelium as if the contractile portion of the inner longitudinal muscles have invaded the epithelium and come to lie between the epithelial cells and the basement membrane. Thus the inner musculature of the bulb is entirely intraepithelial as is the case for Psammorhynchus tubulipenis and Cytocystis clitellatus. The systematic position of M. terminostylisremains uncertain but seems to lie between Psammorhynchus and Cytocystis on one hand and Koinocystididae and Polycystididae on the other.     

The fine structure of Gnathostomulid reproductive organs

Summary The male copulatory organs of five species of Gnathostomulida Scleroperalia have been studied by TEM techniques. These observations provide a more solid basis for classification in the light microscope: inLabidognathia longicollis (fam. Mesognathariidae) the stylet is composed of eight, and inSemaeognathia sterreri, Gnathostomula jenneri, Gnathostomula mediterranea andGnathostomula microstyla (Gnathostomulidae) of ten stylet rods. Each rod consists of a microtubule-filled inner rod, and of an outer rod, filled with crystallized inclusions. The inner rods are continuous with eight — or ten — rod formation cells which are located in the proximal stylet sack. Bipartition of rods occurs by a longitudinal invagination of the basement lamina, underlying the rod cells and the gland cells and continuous with that of the body wall epithelium. InLabidognathia, the outer rods are interlocked, in Gnathostomulidae, the stylet rods are surrounded by an extracellular (cuticular) tube-like stylet sheath of variable fine structure, which is believed to provide extra rigidity. In the species investigated, one single stylet gland, consisting of a monolayered epithelium showing different gland cell types, surrounds the stylet. In the apical gland cell portions, medially and distally membrane-bound secretory granules lie adjacent to the stylet sheath. In Gnathostomulidae, two anterior gland cells are seen in connection with the formation of the stylet sheath. In the muscular sheath the cross-striated fibers, basically derived from the longitudinal body wall musculature, show a tendency towards helical and circumferential arrangement. Musculature is especially prominent in the proximal stylet sack, which is rather a propulsive element than a sperm-storing vesicle, and lacks glands. InGnathostomula species, atrial cells underlie the distal tip of the stylet. The entrance into the male opening is lined with ciliary receptor cells and specialized gland cells.Stylet evolution in Scleroperalia is characterized by progressive differentiation of the muscular sheath, in particular of the proximal stylet sack, and of the stylet — the occurrence of a stylet sheath is seen in connection with increasing diversity of stylet shape.Abbreviations ac atrial cell(s) - ag anterior gland cell(s) - b bursa - bl basal lamina - c rod-crystal in outer rod - cj cuticle of jaw - d desmosome - di dictyosome - e body wall epithelium - ej pharyngeal epithelium - g stylet gland (cell) - gm median gland cell - i gut (cell) - ir inner rod - jc junctional complex - m muscular layer - mo male opening - mv microvillar protrusions - nu nucleus - o ovary - or outer rod - po proximal opening of the proximal stylet sack - ps proximal stylet sack - r stylet rod - rc rod cell - sg secretory granule - sj septate junction - sp sperm - ss stylet sheath - st stylet - te testes - v ventral - z centriole     

Organisation of the praesoma in Acanthocephalus anguillae (Acanthocephala, Palaeacanthocephala) with special reference to the muscular system

The organisation of the praesoma in the parasite Acanthocephalus anguillae was studied on the light and electron microscopic level, with emphasis on the morphology of the musculature. The study was compiled to add new data to the ground pattern of the Acanthocephala for analysis of the phylogenetic relationships within the Gnathifera. In A. anguillae the praesomal epidermis and lemnisci form a coherent syncytium, separated from the epidermis of the trunk. Hooks are seen to be derivatives of the subepidermal basal lamina and are covered by the praesomal epidermis. The praesomal circular body wall musculature forms a network of anastomosing muscle fibres that lines the proboscis; a praesomal longitudinal body wall musculature does not exist. The truncal circular and longitudinal body wall musculature rise up to the praesomal proboscis. The unpaired proboscis retractor, consisting of longitudinal circomyar fibres, forms an outer and an inner concentric tube; the latter extends through the entire praesoma and penetrates the receptacle wall. The sack-like receptacle is surrounded by a receptacle constrictor. The nervous system of the praesoma consists of a prominent cerebral ganglion, three nerves which extend anteriorly, ramify and end within the praesomal musculature, and two strong lateral posterior nerves. A. anguillae lacks an apical organ, lateral organs and a support cell. Many of the features present in the praesoma of A. anguillae can be assumed as ground-pattern characteristics of the Acanthocephala. Accepted: 22 January 2001     

Musculature of the facultative parasite Urastoma cyprinae (Platyhelminthes)

In an effort to understand how the feeding motions of Urastoma cyprinae are generated, the arrangement of its musculature was studied using fluorescence microscopy of phalloidin‐linked fluorescent stains and conventional light histology and transmission electron microscopy. BODIPY 558/568 phalloidin and Alexa 488 phalloidin resolved a meshwork of ribbon‐shaped body‐wall muscles as well as inner‐body musculature associated with the pharynx and male copulatory organ. The general pattern of body‐wall muscles in U. cyprinae is similar to that of other rhabdocoel turbellarians in consisting only of circular, longitudinal, and diagonal fibers; the arrangement of these muscles readily correlates with the bending motions the animal undergoes as it feeds at the surface of gills in bivalves it parasitizes. The orogenital atrium of U. cyprinae lies at the posterior apex of the body, opening at a terminal pore. As evidenced by the arrangement of its epithelium and musculature, it appears to be an invagination of the body wall and comes closest of any such duct studied in turbellarians to satisfying the hypothetical model of a “pseudopharynx,” ostensibly adapted as an organ for swallowing and so supplementing the ingestive role of the animal's true pharynx. J. Morphol. 241:207–216, 1999. © 1999 Wiley‐Liss, Inc.     

Protective buttressing of the hominin face

When humans fight hand‐to‐hand the face is usually the primary target and the bones that suffer the highest rates of fracture are the parts of the skull that exhibit the greatest increase in robusticity during the evolution of basal hominins. These bones are also the most sexually dimorphic parts of the skull in both australopiths and humans. In this review, we suggest that many of the facial features that characterize early hominins evolved to protect the face from injury during fighting with fists. Specifically, the trend towards a more orthognathic face; the bunodont form and expansion of the postcanine teeth; the increased robusticity of the orbit; the increased robusticity of the masticatory system, including the mandibular corpus and condyle, zygoma, and anterior pillars of the maxilla; and the enlarged jaw adductor musculature are traits that may represent protective buttressing of the face. If the protective buttressing hypothesis is correct, the primary differences in the face of robust versus gracile australopiths may be more a function of differences in mating system than differences in diet as is generally assumed. In this scenario, the evolution of reduced facial robusticity in Homo is associated with the evolution of reduced strength of the upper body and, therefore, with reduced striking power. The protective buttressing hypothesis provides a functional explanation for the puzzling observation that although humans do not fight by biting our species exhibits pronounced sexual dimorphism in the strength and power of the jaw and neck musculature. The protective buttressing hypothesis is also consistent with observations that modern humans can accurately assess a male's strength and fighting ability from facial shape and voice quality.     

Ectodermal Wnt signaling regulates abdominal myogenesis during ventral body wall development

Defects of the ventral body wall are prevalent birth anomalies marked by deficiencies in body wall closure, hypoplasia of the abdominal musculature and multiple malformations across a gamut of organs. However, the mechanisms underlying ventral body wall defects remain elusive. Here, we investigated the role of Wnt signaling in ventral body wall development by inactivating Wls or β-catenin in murine abdominal ectoderm. The loss of Wls in the ventral epithelium, which blocks the secretion of Wnt proteins, resulted in dysgenesis of ventral musculature and genito-urinary tract during embryonic development. Molecular analyses revealed that the dermis and myogenic differentiation in the underlying mesenchymal progenitor cells was perturbed by the loss of ectodermal Wls. The activity of the Wnt-Pitx2 axis was impaired in the ventral mesenchyme of the mutant body wall, which partially accounted for the defects in ventral musculature formation. In contrast, epithelial depletion of β-catenin or Wnt5a did not resemble the body wall defects in the ectodermal Wls mutant. These findings indicate that ectodermal Wnt signaling instructs the underlying mesodermal specification and abdominal musculature formation during ventral body wall development, adding evidence to the theory that ectoderm-mesenchyme signaling is a potential unifying mechanism for the origin of ventral body wall defects.     

Anatomy and ultrastructure of ventral pharyngeal organs and their phylogenetic importance in Polychaeta (Annelida)

Summary A comparative anatomical and ultrastructural study of ventral pharyngeal organs (pharyngeal bulbs) was carried out in two species of the Dinophilidae: Dinophilus gyrociliatus and Trilobodrilus axi. Special attention was paid to the fine structure of the stomodeal epithelium, cuticle, glands, muscles, and myoepithelial junctions. The differences between the species are very slight. The pharyngeal organ of the Dinophilidae is characterized by the following features: solid muscle bulbus made up of muscle cells only, bulbus muscle cells with two myofilament systems crossing at an angle of about 90°, gap junctions between these muscle cells, bulbus projects into a pharyngeal sac and bears rostrally a specific epithelium and cuticle, no bulbus glands, no investing (= sagittal) muscles, specific cuticle ultrastructure, cilia of ascending oesophagus with asymmetric tips, specific structure and position of salivary gland openings. The phylogenetic importance of these structures is discussed. Some of these characters are clearly autapomorphic features of the Dinophilidae and no common derived structures to other families with a ventral pharyngeal organ are present. Therefore, it is most likely that the dinophilid pharyngeal organ evolved independently. These findings do not agree with the hypothesis of the unity of the archiannelid families (Polygordiidae, Protodrilidae, Saccocirridae, Nerillidae, Dinophilidae, and Diurodrilidae) established on the basis of an assumed structural similarity of their ventral pharyngeal organs.Abbreviations bb basal body - bep bulbus epithelium - bl basal lamina - bm bulbus muscle - c cilium - cc coelenchyme cell - cm circular muscle - cr caudal rootlet - cu cuticle - dblm dorsal bulbus longitudinal muscle - dlm dorsal longitudinal muscle - dsn dorsal stomatogastric nerve - dy dyad - el electron-dense layer - fl fibrous layer - fi filaments - g Golgi apparatus - gl gland cell - hv homogeneous vesicle - l lipid droplet - la external lamina - lal lamellar layer - ll lower lip - lm longitudinal muscle - ly lysosome - m mitochondrion - mo mouth opening - mt microtubule - mv microvillus - mvp microvillar process - n nucleus - nu nucleolus - oes oesophagus - pcom preoral commissure - phf pharyngeal fold - phl pharyngeal lumen - phs pharyngeal sac - pms peripheral myofilament system - r rootletlike structure - rer rough endoplasmic reticulum - rr rostral rootlet - s sarcoplasmic reticulum - sc salivary canal - scom suboesophageal commissure - sd septate desmosome - ser smooth endoplasmic reticulum - sg secretory granule - sgl salivary gland - sn stomatogastric nerve - st stomach - step stomodeal epithelium - tep transitional epithelium - tf tonofilaments - va vacuole - vlm ventral longitudinal muscle - vsn ventral stomatogastric nerve - z z-element - za zonula adherens     

ON THE DEVELOPMENT OF THE ULTIMOBRANCHIAL GLAND IN AN ANURAN,RANA JAPONICA JAPONICA*

The development of the ultimobranchial gland (UBG) was studied from its earliest emergence in Rana japonica japonica. UBG primordia appear at stage 22 as outfoldings of the pharyngeal epithelium of the 6th visceral pouch in both sides of the body. At stage 24, they separate from the pharyngeal wall, and then become follicular at stage 25. During stages 27–30, which are just prior to metamorphic climax, the UBG seems to be activated, as shown by secondary follicle formation and pseudostratification of the follicle epithelium. At and after the completion of metamorphosis, the UBG shows a histological profile indicating low activity.     

Anaerobic reduction of fumarate in the body wall musculature ofArenicola marina (Polychaeta)

Summary The reduction of fumarate, which is a characteristic feature of anoxic catabolism of some invertebrates, was investigated in mitochondria or mitochondrial fragments prepared from the body wall musculature of the lug-wormArenicola marina (Annelida, Polychaeta).A coupling of the reduction of fumarate to succinate to the oxidation of NADH was demonstrated.The pathway of hydrogen transfer from NADH to fumarate was studied by using specific inhibitors of the respiratory chain. From the results it is concluded that parts of the respiratory chain are involved.During anaerobiosis mitochondria formed succinate at a high rate from malate which had been added as substrate. The formation of succinate is coupled to oxidative phosphorylation. The ratio ATP-production/formation of succinate was found to be 0.6 to 0.8.Succinate formation from malate is inhibited by arsenite and monofluoroacetate.TheK _m for fumarate of the fumarate reductase inArenicola body wall musculature is 2.5×10^–5 M.Abbreviations Ap₅A P¹,P⁵-di(adenosine-5-)pentaphosphate - APAD acetylpyridine adenine dinucleotide - DNP 2,4-dinitrophenol - fw fresh weight (of body wall musculature) - NaFAc sodiummonofluoroacetic acid - PCA perchloric acid - PEP phosphoenolpyruvate Supported by Deutsche Forschungsgemeinschaft (Ze 40/13, Ze 40/14 and Gr 456/5)     

Morphology and ultrastructure of the pharynx in Solenofilomorphidae (Acoela)

The homology of pharynges within the mostly pharynx-less Acoela has been a matter of discussion for decades. Here, we analyze the pharynges of three members of the Solenofilomorphidae, Myopea sp. and two species of the genus Solenofilomorpha, by means of light and transmission electron microscopy. Special focus is placed on the ultrastructure of the pharyngeal musculature, epidermis surrounding the mouth, pharyngeal epithelium, and junction with the digestive parenchyma. The main goal of this study was to evaluate the usefulness of certain characters for broader comparisons within the Acoela. Among the three species, characters relating to position of the mouth, presence and elaboration of sphincter muscles, presence of pharyngeal glands, and ultrastructure of epitheliosomes proved to be variously species- and genus-specific. The arrangement of pharyngeal muscles and their connection with body wall musculature, ultrastructure of receptor cells, and morphology of a nonciliated glandular region in the posterior pharynx, in contrast, appear to be characteristic of the family Solenofilomorphidae and thus of predominant interest for comparisons with other acoel families.     

The structure of the proboscis musculature in <Emphasis Type="Italic">Baseodiscus delineatus</Emphasis> (Delle Chiaje, 1825) (Heteronemertea) and the comparative analysis of the proboscis musculature in heteronemerteans

The proboscis musculature was studied in the nemertean Baseodiscus delineatus using confocal laser scanning and electron transmission microscopy. Three muscle layers were differentiated in the proboscis wall: the outer-longitudinal, the diagonal, and the inner-circular layer. The endothelium consists of two cell types: apical supportive cells with rudimentary cilia and subapical myocytes making up the inner-circular musculature of the proboscis. The supportive cells have thin processes attached to the basal extracellular matrix and their perikarya are spread over the apical surfaces of myocytes. The endothelium of B. delineatus is characterized by a folded basal layer of the extracellular matrix and by different heights of myocyte processes, giving an impression that the inner-circular musculature is multilayered. Comparative analysis shows that the diagonal musculature of Baseodiscus is not homologous to that of other heteronemerteans. An assumption is made that the inner-circular muscles have endothelial origin in all heteronemerteans.     

Formation of Basal Bodies in Ciliary Epithelium of Molluscs Buccinum undatum L. and Lymnaea stagnalis L.

Electron microscopic studies of the leg ciliary epithelium was carried out in two mollusks. In the epithelium of the leg of adult animals, the centrioles were mostly formed de novo with participation of deuterosomes during the formation of basal bodies. Transformation of the centriolar cylinder in a mature basal body is accompanied by the cylinder elongation and appearance of pericentriolar structures, such as rootlet system, basal legs, and basal plate. Centriolegenesis proceeds in both ciliate and nonciliate (with microvilli) cells of the epithelium. It has been proposed that the cell with microvilli represent a transitional stage in differentiation of the ciliary cells.     

Ultrastructural features of the epidermis in turbellaria from the Lake Baikal Geocentrophora wagini (Lecithoepitheliata, Plathelminthes)

The epidermis of Geocentrophora wagini was studied using transmission electron microscopy. The turbellarian body was entirely covered by cilia, whose density was higher on the ventral surface compared with the dorsal one. In all regions examined, the epidermis was made up of a one-layered insunk epithelium. The basal matrix, underlying the epidermis, was a well developed basement membrane (BM) with bilayered structure, overlying the muscle network of circular and longitudinal fibers. The double plasma membranes, extending from the apical surface of epidermis to BM, were linked by specialized cell junctions. This suggested that epidermis had a cellular rather than a cyncytial arrangement. Each insunk epidermal cell was made of two unequal parts: a comparatively thin surface plate attached to BM by hemiadherens junctions, and a massive nucleated portion located below the body wall musculature in the parenchyma. A thin cytoplasmic bridge connected the epidermal plate with the nucleated cell body. The epidermal plates were joined by belt-like junctions along their adjacent surfaces. Inconspicuous zonula adherens (ZA) had a most apical position, and prominent septate junction was arrayed proximally to this zonula. Except ZA, cell boundaries in epidermis were frequently flanked by rows of light tubules and vesicles. In the basal half of the epithelial sheet, they were occassionally accompanied by single cisternae of rough endoplasmic reticulum (RER). The ultrastructure of the insunk cell body and that of the surface plate showed a considerable similarity. The common features were distinctive profiles of RER and GA, the presence of epitheliosomes, light tubules and vesicles, centrioles and fibrous granules. Thus, ultrastructural features allow a rather reliable identification of epidermal cells in the parenchyma, despite the absence of any visible morphological association between cell body and its epidermal plate.