Relating divergence in polychaete musculature to different burrowing behaviors: A study using opheliidae (Annelida)

Divergent morphologies among related species are often correlated with distinct behaviors and habitat uses. Considerable morphological and behavioral differences are found between two major clades within the polychaete family Opheliidae. For instance, Thoracophelia mucronata burrows by peristalsis, whereas Armandia brevis exhibits undulatory burrowing. We investigate the anatomical differences that allow for these distinct burrowing behaviors, then interpret these differences in an evolutionary context using broader phylogenetic (DNA‐based) and morphological analyses of Opheliidae and taxa, such as Scalibregmatidae and Polygordiidae. Histological three‐dimensional‐reconstruction of A. brevis reveals bilateral longitudinal muscle bands as the prominent musculature of the body. Circular muscles are absent; instead oblique muscles act with unilateral contraction of longitudinal muscles to bend the body during undulation. The angle of helical fibers in the cuticle is consistent with the fibers supporting turgidity of the body rather than resisting radial expansion from longitudinal muscle contraction. Circular muscles are present in the anterior of T. mucronata, and they branch away from the body wall to form oblique muscles. Helical fibers in the cuticle are more axially oriented than those in undulatory burrowers, facilitating radial expansion during peristalsis. A transition in musculature accompanies the change in external morphology from the thorax to the abdomen, which has oblique muscles similar to A. brevis. Muscles in the muscular septum, which extends posteriorly to form the injector organ, act in synchrony with the body wall musculature during peristalsis: they contract to push fluid anteriorly and expand the head region following a direct peristaltic wave of the body wall muscles. The septum of A. brevis is much thinner and is presumably used for eversion of a nonmuscular pharynx. Mapping of morphological characters onto the molecular‐based phylogeny shows close links between musculature and behavior, but less correlation with habitat. J. Morphol. 275:548–571, 2014. © 2014 Wiley Periodicals, Inc.     

Oligochaetes (Naididae, Tubificidae, Opistocystidae, Enchytraeidae, Sparganophilidae and Alluroididae) of Guyana

About 50 species in more than 20 genera of the microdrile oligochaete families Tubificidae, Naididae, Opistocystidae, and Enchytraeidae and the freshwater megadrile families Sparganophilidae and Alluroididae were identified in recent collections made in Guyana. Only seven species in these families were previously recorded from Guyana. The aquatic oligochaete fauna has similar components to those of the southeastern United States, other locations in South America, and across lower latitudes in the northern hemisphere. A high diversity of species is found in the naidids especially in the genera Pristina and Pristinella, especially considering the small number of locations that have been sampled. The collections include approximately 12 new species of rhyacodrilines (Tubificidae), Dero, Pristina, Pristinella (Naididae), Brinkhurstia (Alluroididae), Hemienchytraeus and Aspidodrilus (Enchytraeidae). This is the first record of Aspidodrilus from outside of Africa and the first new record since 1952.     

External sense receptors in microdrile oligochaetes (Annelida,Clitellata) as revealed by scanning electron microscopy: Typology and patterns of distribution in the main taxonomic groups

This work summarizes the observations on 30 species of microdriles belonging to the families Naididae (Rhyacodrilinae, Pristininae, Naidinae, Phallodrilinae, and Tubificinae), Phreodrilidae, Lumbriculidae, and Enchytraeidae using scanning electron microscopy. The lumbricid Eiseniella tetraedra, a megadrile species common in typical microdrile habitats, was used for comparison. Microdriles display external ciliate sense structures along the entire body; even at the clitellum and in budding and regeneration zones. According to the shape of the cilia, these sense structures can be divided into receptors of blunt cilia, receptors of sharp cilia, and composed receptors. Sense receptors can be morphologically unconspicuous or clearly defined on sensory buds or papillae. All microdriles studied have receptors of blunt cilia. Enchytraeids have characteristic receptors of short cilia. Pristina (Pristininae), Chaetogaster, Ophidonais, and Stylaria (Naidinae) have receptors of long blunt cilia. Composed receptors were found only in some microdriles and E. tetraedra. Receptors of sharp cilia have been found in most microdriles. Enchytraeids might be the only exception, but sharp cilia are probably present in the amphibiotic Cognettia sphagnetorum. Sensory cells with long sharp cilia might play a rheoreceptor role, and their presence in E. tetraedra and C. sphagnetorum would imply the reappearing of an ancient character that was probably lost with the transit from aquatic to terrestrial habitats. Some lumbriculids have ciliated fields. Anatomically, these structures appear as intermediate between the typical isolate sensory structures of microdriles and the sensillae of the hirudineans. The general pattern in microdriles is that uniciliate receptors and multiciliate receptors are separated, which supports the presumed aquatic origin of the clitellates. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Marine Oligochaeta from the Koster Area, West Coast of Sweden, with Descriptions of Two New Enchytraeid Species

A total of 28 species of marine Oligochaeta (belonging to the families Naididae, Tubificidae and Enchytraeidae) are reported from eulittoral and sublittoral sediment samples taken in the Koster area on the Swedish West Coast. Lumbricillus algensis sp.n. and Grania ovitheca sp.n. are described and their morphological and taxonomical relations to other enchytraeids are discussed. L. algensis is characterized mainly by its spermathecae, which project into segment VI, and by its very large penial bulbs. G. ovitheca possesses no dorsal setae, the ventral setae being present posterior to the clitellum only, and its spermathecae consist of a narrow duct and a large egg-shaped to oval ampulla, filling most of the coelom of segment V. Four sublittoral species, Limnodriloides barnardi (Tubificidae), Lumbricillus semifuscus, Marionina sublitoralis and Grania roscoffensis (all Enchytraeidae) are reported as new to the Swedish fauna.     

Cutinsomes as building‐blocks of Arabidopsis thaliana embryo cuticle

Cutinsomes, spherical nanoparticles containing cutin mono‐ and oligomers, are engaged in cuticle formation. Earlier they were revealed to participate in cuticle biosynthesis in Solanum lycopersicum fruit and Ornithogalum umbellatum ovary epidermis. Here, transmission electron microscopy (TEM) and immunogold labeling with antibody against the cutinsomes were applied to aerial cotyledon epidermal cells of Arabidopsis thaliana mature embryos. TEM as well as gold particles conjugated with the cutinsome antibody revealed these structures in the cytoplasm, near the plasmalemma, in the cell wall and incorporated into the cuticle. Thus, the cutinsomes most probably are involved in the formation of A. thaliana embryo cuticle and this model plant is another species in which these specific structures participate in the building of cuticle in spite of the lack of the lipotubuloid metabolon. In addition, a mechanism of plant cuticle lipid biosynthesis based on current knowledge is proposed.     

Genetic variation and phylogeny of Scandinavian species of Grania (Annelida: Clitellata: Enchytraeidae), with the discovery of a cryptic species

Individuals of five nominal species of Grania (Annelida: Clitellata: Enchytraeidae) were collected from locations in Sweden, Norway and France, for studies on the intraspecific variation at the Cytochrome Oxidase I (COI) locus of mitochondrial DNA and internal transcribed spacer (ITS) region of nuclear DNA. It was found that the previously described morphospecies in general contain low variation compared to the between‐species variation in both loci. In one instance, however, an individual morphologically indistinguishable from G. ovitheca was found to be deviant and instead cluster with G. postclitellochaeta both by COI and ITS. We describe this individual as a new species: G. occulta sp.n. Furthermore, phylogenetic analyses were conducted, showing a close relationship between G. variochaeta, G. occulta, G. ovitheca and G. postclitellochaeta, as well as between G. pusilla and G. maricola. Using the results from the phylogenetic analyses, we discuss the evolution of morphological characters in Scandinavian species of Grania.     

Comparative myoanatomy of cycliophoran life cycle stages

The metazoan phylum Cycliophora includes small cryptic epibionts that live attached to the mouthparts of clawed lobsters. The life cycle is complex, with alternating sexual and asexual generations, and involves several sessile and free‐living stages. So far, the morphological and genetic characterization of cycliophorans has been unable to clarify the phylogenetic position of the phylum. In this study, we add new details on the muscular anatomy of the feeding stage, the attached Prometheus larva, the dwarf male, and the female of one of the two hitherto described species, Symbion pandora. The musculature of the feeding stage is composed of myofibers that run longitudinally in the buccal funnel (two fibers) and in the trunk (variable number of fibers). The mouth opening is lined by a myoepithelial ring musculature. A complex myoepithelial sphincter is situated proximal to the anus. In the attached Prometheus larva, three longitudinal sets of myofilaments run dorsally, laterally, and ventrally along the entire anterior‐posterior body axis. The muscular architecture of the dwarf male is complex, especially close to the penis, in the posterior part of the body. An X‐shaped muscle structure is found on the dorsal side, whereas on the ventral side, longitudinal muscles and a V‐shaped muscle structure are present. These muscles are complemented by additional dorsoventral muscles. The mesodermal muscle fibers attach to the cuticle via the epidermis in all life cycle stages studied herein. The musculature of the female is similar to that of the Pandora larva of Symbion americanus and includes dorsoventral muscles and longitudinal muscles that run in the dorsal and ventral body region. Overall, our results reveal striking similarities in the muscular arrangement of the life cycle stages of both Symbion species. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Cutinsomes and lipotubuloids appear to participate in cuticle formation in Ornithogalum umbellatum ovary epidermis: EM–immunogold research

The outer wall of Ornithogalum umbellatum ovary and the fruit epidermis are covered with a thick cuticle and contain lipotubuloids incorporating ³H-palmitic acid. This was earlier evidenced by selective autoradiographic labelling of lipotubuloids. After post-incubation in a non-radioactive medium, some marked particles insoluble in organic solvents (similar to cutin matrix) moved to the cuticular layer. Hence, it was hypothesised that lipotubuloids participated in cuticle synthesis. It was previously suggested that cutinsomes, nanoparticles containing polyhydroxy fatty acids, formed the cuticle. Thus, identification of the cutinsomes in O. umbellatum ovary epidermal cells, including lipotubuloids, was undertaken in order to verify the idea of lipotubuloid participation in cuticle synthesis in this species. Electron microscopy and immunogold method with the antibodies recognizing cutinsomes were used to identify these structures. They were mostly found in the outer cell wall, the cuticular layer and the cuticle proper. A lower but still significant degree of labelling was also observed in lipotubuloids, cytoplasm and near plasmalemma of epidermal cells. It seems that cutinsomes are formed in lipotubuloids and then they leave them and move towards the cuticle in epidermal cells of O. umbellatum ovary. Thus, we suggest that (1) cutinsomes could take part in the synthesis of cuticle components also in plant species other than tomato, (2) the lipotubuloids are the cytoplasmic domains connected with cuticle formation and (3) this process proceeds via cutinsomes.     

Organization and differentiation of the body-wall musculature in Macrostomum (Turbellaria,Macrostomidae)

We studied the body-wall musculature, its ECM (extracellular matrix), and the junctional complexes between muscle cells and between muscle cells and ECM in Macrostomum hystricinum marinum Rieger, 1977, using Nomarski-contrast and electron microscopy. Differentiation of these body-wall components was followed by monitoring embryonic stages at 52%, 64%, and 82% of the time between egg-laying and hatching and with study of the hatchling and adult stages. For comparison, the body-wall musculature of other macrostomidans has been examined in conventional light-histological sections.Muscles form a grid of longitudinally, diagonally, and circularly oriented fibers beneath the epidermis in M. hystricinum marinum and this orientation of cells can be found already in embryos at 64% development. Younger embryos at 52% development show no muscle differentiation. The ECM forms a net-like arrangement that apparently envelops the individual muscle cells. Characteristic knob-like thickenings of the ECM occur at the base of the epidermis. Muscle cells attach to each other, to the epidermis, and to other cell types through hemidesmosome-like junctions at thickenings of the ECM in the adult and hatchling stages; no true desmosomes exist between muscle cells. Gap junctions occur commonly between longitudinal muscles of adult specimens and between perikarya of muscle cells in embryos at 64% and 82% development.More comparative studies are needed to determine the systematic value of presence or absence of the diagonal muscle fibers in the body wall of turbellarians.     

Skeleto‐musculature of the mandible and its function in podocopid ostracodes exemplified by Loxoconcha pulchra (Cytheroidea: Loxoconchidae) and Fabaeformiscandona tyrolensis (Cypridoidea: Candonidae)

A new anatomical interpretation of the skeleto‐musculature of the mandible in podocopid ostracodes is proposed based on ultrastructural observations of Loxoconcha pulchra Ishizaki, 1968 and Fabaeformiscandona tyrolensis (Löffler, 1963). Attachment cells with their numerous microfibers anchor the sclerotized lamella cuticle (chitinous rod) to the outer lamella cuticle via intracuticular fibers. A pan‐shaped structure develops at the attachment area in the outer lamella cuticle and is responsible for the mandibular scar. The sclerotized lamella cuticle is continuous with the dorsal apex of the mandibular coxa, which touches the fulcral point directly without intermediate epidermis. The calcification of the fulcral point starts immediately after ecdysis and this rapid calcification suggests that the fulcral point must play a significant role in functional morphology of podocopid ostracodes. After 3D‐reconstruction of the set of mandibular extrinsic muscles in a podocopid ostracode, we suggest that the fulcral point is a key character for carapace opening by transmitting the force from the mandibular coxa to the valve and at the same time functions as the stable fulcrum for mandibular movement during mastication. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Comparative study of the cuticle in some aquatic oligochaetes (Annelida: Clitellata)

An examination of the cuticle of six aquatic oligochaete species using transmission electron microscopy revealed a larger morphological variation than previously known. Three freshwater species, Aulodrilus pluriseta, Spirosperma ferox (both Tubificidae), and Pristina breviseta (Naididae), and three marine species, Clitellio arenarius, Heterochaeta costata (both Tubificidae), and Paranais litoralis (Naididae), were investigated. The arrangement of the collagen fibers in the cuticle differs among the studied species. Only S. ferox shows an "orthogonal grid," i.e., layers of parallel fibers perpendicular to each other, as earlier described for lumbricids and enchytraeids. Clitellio arenarius and H. costata have fibers arranged in layers, while A. pluriseta and P. litoralis have irregularly distributed fibers. Pristina breviseta lacks cuticular fibers. The matrix surrounding the collagen fibers (when present) continues outside the fiber layer, making up a thin epicuticle, which has a unique banding in each of the studied species. The external surface of the epicuticle is covered with epicuticular projections. Their number, shape, and attachment to the epicuticle vary among the studied species. Furthermore, a distinctive internal substructure of the projections was observed in H. costata, A. pluriseta, S. ferox, and P. breviseta. Microvilli, extensions from the epidermal cells, penetrate the cuticle and terminate at its outer surface. In three species microvilli were observed to pinch off the epicuticular projections. The size, number, and shape of the latter vary; no typical microvilli were observed in S. ferox.     

Phylogeny of oligochaetous Clitellata

Clitellata, with more than one third of all annelid species described, is briefly introduced, and an overview of the hypotheses of phylogenetic relationships among the groups traditionally referred to as oligochaetes is given. The presentation is placed in a historical context and describes the trend to move from intuitive, narrative approaches to more formal analyses of character patterns. Monophyly of the earthworms (the megadriles, or Metagynophora sensu Jamieson), or at least a major part of them (Crassiclitellata sensu Jamieson), and paraphyly of the ‘microdrile’ largely aquatic, groups are supported by both morphological and molecular data. Further, DNA sequences as well as spermatozoal ultrastructure corroborate that all leech-like taxa (Hirudinida, Acanthobdellida and Branchiobdellida) constitute a clade derived within ‘Oligochaeta’, closely related to the family Lumbriculidae. Molecular systematic studies also support relationships already identified on the basis of morphological data, e.g., the position of Naididae within Tubificidae, the position of Phreodrilidae close to, but outside, the same family, and the putative sistergroup relationship between the newly discovered Capilloventridae and the rest of Clitellata. A recent study using 18S rDNA suggests that Enchytraeidae is closely related to Metagynophora, and that these two taxa, which contain all terrestrial oligochaetous clitellates, form a clade derived from aquatic ‘microdriles’ This refutes a recent hypothesis proposing that the ancestor of Clitellata was terrestrial. To a great extent, however, the basal resolution of the oligochaetous clitellates remains unclear.     

Ultrastructure of phaosomous photoreceptors in Stylaria lacustris (Naididae, ‘Oligochaeta’, Clitellata) and their importance for the position of the Clitellata in the phylogenetic system of the Annelida

Many species of Naididae possess a pair of pigmented eyes. Within Clitellata, eyes are generally present in Hirudinea, whereas Naididae are the only oligochaete taxon having these sense organs. The eyes of Naididae are epidermal structures and consist of a multicellular pigment cup in which a single row of five to six photoreceptor cells is embedded. The sensory cells are typical phaosomes: the photoreceptive structures (microvilli) project into a cavity formed by the sensory cell itself. In Stylaria lacustris this cavity opens to the exterior, clearly documenting that it represents an invagination of the apical cell membrane. The density of sensory microvilli is comparatively low and a central vitreous body is lacking. Similar phaosomous photoreceptors, not associated with either pigmented or unpigmented supporting cells, occur in the epidermis of the anterior end. These photoreceptors correspond to those found in other Clitellata, confirming that phaosomes are the only known type of photoreceptor cell occurring in this taxon. As a result of their simple structure they have been regarded as plesiomorphic for Annelida. However, an out‐group comparison with eyes and photoreceptors occurring in polychaetes and other spiralians reveals that they, in fact, are a rather specialized type of photoreceptor. Despite the simple structure, they most likely represent an autapomorphy of Clitellata. It follows that in all probability, these phaosomes are a secondarily evolved type of photoreceptor, which arose within the oligochaete clade after the primary photoreceptors present in the out‐groups had been lost. This loss might have occurred during evolution of a burrowing life style within the sediment and subsequent invasion of the terrestrial environment.     

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     

Ultrastructure of the lycophora larva of Gyrocotyle urna (Cestoda,Gyrocotylidea)

Summary The fine structure of the ciliated epidermis, the body musculature and the neodermis anlage cells of the free-swimming lycophora larva of Gyrocotyle urna Grube and Wagener, 1852, is described. The epidermis is syncytial and covers the whole body including a caudal cavity into which the larval hooks protrude. It contains several types of vesicles, mitochondria and membrane whorls but lacks nuclei, dictyosomes and endoplasmic reticulum. The locomotory cilia exhibit single rostrally directed rootlets. The body musculature consists of about 25 longitudinal and 42 circular muscles. Their nuclei are located proximally to the contractile elements. The neodermis anlage cells show numerous dictyosomes, elaborated cisternae of endoplasmatic reticulum, typical coated vesicles and membranous bodies. Extrusions of these cells do not penetrate the epidermis but contact it by desmosoms.The evolution of epidermal and neodermal structures of Gyrocotyle and other parasitic Platyhelminthes is discussed. The probable consequences of the lack of some types of organelles in the epidermis of Neodermata are considered.Abbreviations bb basal body - bl basal lamina - ci locomotory cilia - Ce epidermis of the caudal cavity - cr ciliary rootlet - di dictyosome - Ep epidermis - er endoplasmic reticulum - Hm hook musculature - ld lipid droplet - Lh larval hook - Lm longitudinal musculature - mi mitochondria - mt microtubule - mv microvilli - mw membrane whorl - Ne neodermis anlage cell - nu nucleus - Re receptor - Rm circular musculature - ve vesicles     

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     

The adult musculature of two pseudostomid species reveals unique patterns for flatworms (Platyhelminthes,Prolecithophora)

We analyzed the adult musculature of two prolecithophoran species, Cylindrostoma monotrochum (von Graff, 1882) and Monoophorum striatum (von Graff, 1878) using a phalloidin-rhodamine technique. As in all rhabdithophoran flatworms, the body-wall musculature consisted of three muscle layers: on the outer side was a layer of circular muscle fibers and on the inner side was a layer of longitudinal muscle fibers; between them were two different types of diagonally orientated fibers, which is unusual for flatworms. The musculature of the pharynx consisted of a basket-shaped grid of thin longitudinal and circular fibers. Thick anchoring muscle fibers forming a petal-like shape connected the proximal parts of the pharynx with the body-wall musculature. Male genital organs consisted of paired seminal vesicles, a granular vesicle, and an invaginated penis. Peculiar ring-shaped muscles were only found in M. striatum, predominantly in the anterior body part. In the same species, seminal vesicles and penis only had circular musculature, while in C. monotrochum also longitudinal musculature was found in these organs. Female genital organs were only present in M. striatum, where we characterized a vagina interna, and a bursa seminalis. Transverse, crossover, and dorsoventral muscle fibers were lacking in the middle of the body and greatly varied in number and position in both species.