The musculature of the praesoma in Macracanthorhynchus hirudinaceus (Acanthocephala, Archiacanthocephala): re-examination and phylogenetic significance

The endoparasitic Archiacanthocephala (Acanthocephala) consist of the Aporhynchida, Moniliformida, Gigantorhynchida and Oligacanthocephala. In the present study the organisation of the praesoma in Macracanthorhynchus hirudinaceus (Archiacanthocephala, Oligacanthorhynchida) was investigated by light microscopy based on series of semithin sections (5 µm) with special emphasis on the musculature. The study was carried out to substantiate the ground pattern of the Acanthocephala and to elucidate the phylogenetic relationships within the Archiacanthocephala. A comparison of the presented morphology in M. hirudinaceus with literature data leads to the assumption that the muscle plate and the midventral longitudinal muscle evolutionarily originated from the circular musculature of the praesoma and the receptacle, respectively. Whereas the midventral longitudinal muscle probably represents an autapomorphy of the taxon Oligacanthorhynchida, a muscle plate can be regarded as an autapomorphy of a monophylum consisting of the Moniliformida, Gigantorhynchida and Oligacanthorhynchida. Moreover, the outer wall in species with a double-walled receptacle probably corresponds to the receptacle protrusor or receptacle constrictor in species with a single-walled receptacle, and thus not only a receptacle but also an additional surrounding muscle can be assumed for the ground pattern of the Acanthocephala. For a better comparability the discussion includes a tabular survey of the synonyms used in the literature.     

A morphological study of the anterior nervous system of the praesoma of Neoechinorhynchus cylindratus (Acanthocephala: Neoechinorhynchidae)

The nerve pathways in the praesoma, based on light microscopy of serial transverse, sagittal, and longitudinal sections stained with Ehrlich's acid hematoxylin are described for the first time for a memeber of Neoechinorhynchus. The route from the cerebral ganglion to the musculature and sense organs of the proboscis and body wall for 11 nerves, five pair and one single, the presence and structure of the Stutzzelle (support cell) and its association with the neck sense organs are described. A comparison with the nervous system in the praesoma of Paulisentis fractus is discussed.     

A morphological study of the nervous system of the praesoma of Octospinifer macilentus (Acanthocephala: Noechinorhynchidae)

The nerve pathways in the praesoma are described for the first time for a member of the genus Octospinifer. Eleven nerves, five paired, and one single, are traced from the cerebral ganglion to their associations with the musculature of the body wall, neck sense organs, and the musculature of the proboscis wall and the invertor muscles of the proboscis. The structure and location of the Stützzelle (support cell) and its association with the neck sense organs are described. A comparison with the nervous system in the praesoma of Noechinorhynchus and Paulisentis is discussed.     

A morphological study of the nervous system of the praesoma of Paulisentis fractus (Acanthocephala: Neoechinorhynchidae)

The nerve pathways in the praesoma are described for a member of the class Eoacanthocephala for the first time. Eleven nerves, five paired and one single, are traced from the cerebral ganglion to their associations with the musculature of the body wall, neck sense organs, and the musculature of the proboscis wall and the invertor muscles of the proboscis. The structure and location of the stutzzelle and series of nerve endings in the hypodermis of the body wall and at the apex of the proboscis are described.     

The nervous system in the praesoma of Echinorhynchus salmonis (Acanthocephala: Echinorhynchidae)

Based on light microscopic observations, nerve pathways are described for the first time in the praesoma of a species of the Echinorhynchidae. The pathways are described for 18 nerves, 8 paired and 2 single, which originate from the cerebral ganglion and a post-ganglionic cell and terminate in the body wall musculature and the proboscis. The location of two commissures formed by these nerves is also described.     

Praesomal nerves in Leptorhynchoides thecatus (Acanthocephala: Rhadinorhynchidae).

Investigated by light microscopy, the nerve pathways are described for the first time in the praesoma of a species of Rhadinorhynchidae. The pathways are described for 18 nerves, eight paired and two single, which originate from the cerebral ganglion and a post-ganglionic cell and terminate in the body wall musculature and the proboscis. The location of three commissures formed by these nerves is also described.     

The neuroactive substances and associated muscle system in Rhipidocotyle campanula (Digenea,Bucephalidae) from the intestine of the pike Esox lucius

We report about the muscular system and the serotonergic and FMRFamidergic components of the nervous system of the Bucephalidae trematode, Rhipidocotyle campanula, an intestinal parasite of the pike. We use immunocytochemical methods and confocal scanning laser microscopy (CLSM). The musculature is identified by histochemical staining with fluorescently labeled phalloidin. The body wall musculature of R. campanula contains three layers of muscle fibres – the outer thin circular, intermediate longitudinal and inner diagonal muscle fibres running in two opposite directions. The digestive system of R. campanula possess of a well-developed musculature: radial, longitudinal and circular muscle elements are detected in the pharynx, circular and longitudinal muscle filaments seen in the oesophagus, and longitudinal and the circular muscle fibres were found in the intestinal wall. Specific staining indicating the presence of actin muscle filaments occurs in the cirrus sac localized in the posterior body region. The frontal region of anterior attachment organ, the rhynchus, in R. campanula is represented by radial muscle fibres. The posterior part of the rhynchus comprise of radial muscles forming the organ's wall, and several strong longitudinal muscle bundles. Serotonergic and FMRFamidergic structures are detected in the central and peripheral compartments of the nervous system of R. campanula, that is, in the paired brain ganglia, the brain commissure, the longitudinal nerve cords, and connective nerve commissures. The innervations of the rhynchus, pharynx, oesophagus and distal regions of the reproductive system by the serotonergic and FMRFamidergic nervous elements are revealed. We compare our findings obtained on R. campanula with related data for other trematodes.     

The burrowing of Priapulus caudatus

An account is given of the way in which Priapulus caudatus burrows in the muddy sea-bed in which it lives. Three phases are distinguishable in the muscular activity which is responsible for locomotion. During the first phase the animal is able to feed and defaecate, during the second the proboscis becomes invaginated, and during the third the animal moves forward. The power for locomotion is provided by contraction of the longitudinal and circular muscles of the body wall, not, as has been suggested previously, by the retractor muscles of the praesoma. Invagination of the proboscis is apparently stimulated by the arrival of a wave of contraction in the body wall musculature, propagated from the trunk.
In general the animal burrows in a way common for soft-bodied animals; the anterior and posterior extremities acting in turn as "terminal" and "penetration" anchors in the substratum. The muscular activities of the larva are limited by the presence of a lorica which encases the trunk, and the animal's powers of movement at this stage are very restricted.     

Myoanatomy and serotonergic nervous system of plumatellid and fredericellid phylactolaemata (lophotrochozoa,ectoprocta)

The phylogenetic position of the Ectoprocta within the Lophotrochozoa is discussed controversially. For gaining more insight into ectoproct relationships and comparing it with other potentially related phyla, we analysed the myoanatomy and serotonergic nervous system of adult representatives of the Phylactolaemata (Plumatella emarginata, Plumatellavaihiriae, Plumatella fungosa, Fredericella sultana). The bodywall contains a mesh of circular and longitudinal muscles. On its distal end, the orifice possesses a prominent sphincter and continues into the vestibular wall, which has longitudinal and circular musculature. The tentacle sheath carries mostly longitudinal muscle fibres in Plumatella sp., whereas F. sultana also possesses regular circular muscle fibres. Three groups of muscles are associated with the lophophore: 1) Lophophoral arm muscles (missing in Fredericella), 2) epistome musculature and 3) tentacle musculature. The epistome flap is encompassed by smooth muscle fibres. A few fibres extend medially over the ganglion to its proximal floor. Abfrontal tentacle muscles have diagonally arranged muscle fibres in their proximal region, whereas the distal region is formed by a stack of muscles that resemble an inverted ‘V’. Frontal tentacle muscles show more variation and either possess one or two bases. The digestive tract possesses circular musculature which is striated except at the intestine where it is composed of smooth muscle fibres. The serotonergic nervous system is concentrated in the cerebral ganglion. From the latter a serotonergic nerve extends to each tentacle base. In Plumatella the inner row of tentacles at the lophophoral concavity lacks serotonergic nerves. Bodywall musculature is a common feature in many lophotrochozoan phyla, but among other filter feeders like the Ectoprocta is only present in the ‘lophophorate’ Phoronida. The longitudinal tentacle musculature is reminiscent of the condition found in phoronids and brachiopods, but differs to entoproct tentacles. Although this study shows some support for the ‘Lophophorata’, more comparative analyses of possibly related phyla are required. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

Functional morphology of the Conus proboscis (Mollusca: Gastropoda)

The extended proboscis of the toxoglossan gastropod Conus may exceed four times its contracted length and 1.5 times the shell length. The proboscis wall consists of cuboidal epidermis and circular, crossed helical and longitudinal muscle layers. Between the proboscis wall and its lumen, free longitudinal muscles and nerves course through haemocoel. A thick layer of connective tissue and columnar epithelium surround the proboscis lumen. In C. Catus , muscle comprises about 70% of the volume of the proboscis (exclusive of its lumen) and haemocoel about 20%, in both moderately extended and contracted states. Differentiation along the length of the proboscis includes gradual replacement of muscle by connective tissue distally in the proboscis wall, and a subapical sphincter muscle that probably prevents back-slippage of the detached radular tooth prior to its use in feeding and aids injection of the tooth into the prey during capture.     

Presomal morphology and development of Prosthorhynchus formosus,Prosthenorchis elegans,and Moniliformis dubius (Acanthocephala)

Larvae removed at one-day intervals from laboratory infected intermediate hosts provided material for a comparative study of presomal development in Prosthorhynchus formosus (Van Cleave, '18) Travassos, '26, Prosthenorchis elegans (Diesing, 1851) Travassos, '15, and Moniliformis dubius Meyer, '33. Acanthellae begin development soon after entering intermediate hosts' hemocoels, and by the 18th day all three species possess three nuclear masses representing primordia of the proboscis, proboscis receptacle and ganglion, and trunk musculature and genitalia. Presomal development of P. formosus and P. elegans results in structures concurring with morphology of other adult palaeacanthocephalans and archiacanthocephalans. Development of M. dubius, however, differs from that of other archiacanthocephalans in that the muscular receptacle wall lines the entire surface of the nonmuscular sheath, failing to form a ventral cleft characteristic of other archiacanthocephalans. Unlike receptacle protrusor muscles of other archiacanthocephalan species, those of M. dubius spiral around the receptacle as they extend posteriad to attach individually to a pouchlike, muscular thickening at the receptacle's base. These protrusor muscles are distinct from the receptacle wall, as attested by their development alongside neck retractor muscles, not from the receptacle primordium, and the manner in which they are left to trail behind the receptacle when it is drawn anteriorly into the proboscis during larval development. The proboscis receptacle of M. dubius should not be thought of as being double-walled, as envisioned by previous workers.     

A new genus and species of monostiliferous hoplonemertean (Nemertea: Enopla: Monostilifera) from Japan

A new genus and species of monostiliferous hoplonemertean, Diopsonemertes acanthocephala gen. et sp. nov., is described from Otsuchi Bay, Japan. Significant anatomical features of the new form include a body wall longitudinal musculature anteriorly divided into inner and outer layers by connective tissue, no pre-cerebral septum, the presence of a thin coat of diagonal muscle fibres between the body wall longitudinal and circular muscle layers in the foregut body region, cephalic retractor muscles derived only from the inner portion of the divided longitudinal muscles and a rhynchocoel more than half the body length.     

Three-dimensional reconstruction of the musculature of Cossura pygodactylata Jones, 1956 (Annelida: Cossuridae)

The musculature of adult specimens of Cossura pygodactylata was studied by means of F-actin labelling and confocal laser scanning microscopy (CLSM). Their body wall is comprised of five longitudinal muscle bands: two dorsal, two ventral and one ventromedial. Complete circular fibres are found only in the abdominal region, and they are developed only on the border of the segments. Thoracic and posterior body regions contain only transverse fibres ending near the ventral longitudinal bands. Almost-complete rings of transverse muscles, with gaps on the dorsal and ventral sides, surround the terminal part of the pygidium. Four longitudinal bands go to the middle of the prostomium and 5–14 paired dorso-ventral muscle fibres arise in its distal part. Each buccal tentacle contains one thick and two thin longitudinal muscle filaments; thick muscle fibres from all tentacles merge, forming left and right tentacle protractors rooted in the dorsal longitudinal bands of the body wall. The circumbuccal complex includes well-developed upper and lower lips. These lips contain an outer layer of transverse fibres, and the lower lip also contains inner oblique muscles going to the dorsal longitudinal bands. The branchial filament contains two longitudinal muscle fibres that do not connect with the body musculature. The parapodial complex includes strong intersegmental and segmental oblique muscles in the thoracic region only; chaetal retractors, protractors and muscles of the body wall are present in all body regions. Muscle fibres are developed in the dorsal and ventral mesenteries. One semi-circular fibre is developed on the border of each segment and is most likely embedded in the dissepiment. The intestine has thin circular fibres along its full length. The dorsal blood vessel has strong muscle fibres that cover its anterior part, which is called the heart. It consists of short longitudinal elements forming regular rings and inner partitions. The musculature of C. pygodactylata includes some elements that are homologous with similar muscular components in other polychaetes (i.e., the body wall and most parapodial muscles) and several unique features, mostly at the anterior end.     

Muscular system in polychaetes (Annelida)

The structure of the polychaete muscular system is reviewed. The muscular system comprises the muscles of the body wall, the musculature of the parapodial complex and the muscle system of the dissepiments and mesenteries. Various types of organisation of the longitudinal and circular components of the muscular body wall are distinguished. In Opheliidae, Polygordiidae, Protodrilidae, Spionidae, Oweniidae, Aphroditidae, Acoetidae (=Polyodontidae), Polynoidae, Sigalonidae, Phyllodocidae, Nephtyidae, Pisionidae, and Nerillidae circular muscles are lacking. It is hypothesised that the absence of circular muscles represents the plesiomorphic state in Annelida. This view contradicts the widely accepted idea of an earthworm-like musculature of the body wall comprising an outer layer of circular and an inner layer of longitudinal fibres. A classification of the various types of parapodial muscle construction has been developed. Massive and less manoeuvrable parapodia composed of many components like those of Aphrodita are regarded to represent the plesiomorphic state in recent polychaetes. An analysis of the diversity of the muscular structure supports the hypothesis that the primary mode of life in polychaetes was epibenthic and the parapodial chaetae had a protective function.     

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     

A new mangrove-dwelling nemertean from China

Nemertean specimens were collected from the mangrove zone in the estuary of Jiulong Jiang River. Histological studies revealed that they belong to genus Pantinonemertes but differed from the known taxa of the genus. In the present paper they are described as a new species, Pantinonemertes fujianensis sp. nov. The immature specimens, with the body rounded anteriorly and somewhat dorso-ventrally flattened in intestinal region, measured about 85–120 mm long and 1.5–2.0 mm wide. Dark pigment is concentrated along the mid-dorsal line to form a longitudinal stripe that extends for most of the body length. The head possesses a pair of horizontal longitudinal furrows, a pair of oblique lateral furrows and four eyes. A precerebral septum is absent. The proboscis is well developed and possesses 19 large proboscis nerves. The frontal organ is a well-developed tubular structure, with the epithelium regionally differentiated. Cephalic glands are extensive, consisting of faintly stained small glands that open into the frontal organ, large blocks of clear gland and orange-staining glands (stained with Mallory triple method) that open through the ducts penetrating the body wall. The excretory system consists of numerous binucleate flame cells especially in the anterior body region, each flame cell possesses 7–9 transverse cuticular support rings. Excretory tubules either open to exterior via the efferent ducts penetrating the body wall or open into the frontal organ. Lateral nerve cords are without accessory lateral nerves.     

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