Body wall muscles in the haplotaxidsHaplotaxis gordioides andPelodrilus leruthi (Annelida,Oligochaeta)

Summary The muscle organization of the body wall in two species of Haplotaxida is described.Haplotaxis gordioides andPelodrilus leruthi show significant differences in the longitudinal muscle layer. The observations suggest that inH. gordioides, the muscle fibres could foreshadow the flat circomyarian organization of microdrile muscles, while theP. leruthi organization recalls the pinnate arrangement of megadrile body wall.     

Myogenesis in two polyclad platyhelminths with indirect development,Pseudoceros canadensis and Stylostomum sanjuania

SUMMARY Myogenesis of two representatives of Platyhelminthes, Stylostomum sanjuania and Pseudoceros canadensis, was followed from egg deposition until well‐differentiated free‐swimming larval stages, using F‐actin staining and confocal laserscanning microscopy. Zonulae adhaerentes are the only structures to stain before 50% of development between egg deposition and hatching in S. sanjuania, and before 67% of development in P. canadenis. Subsequently, irregular fibers appear in the embryo, followed by a helicoid muscle close to the apical pole. Three longitudinal muscle pairs form, of which the dorsal pair remains more pronounced than the others. Gradually, new muscles form by branching or from double‐stranded muscle zones adjacent to existing muscles. This results in an elaborate muscular bodywall that consists of a single helicoid muscle as well as multiple circular and longitudinal muscles. Diverse retractor muscles insert at the sphincter muscles around the stomodeum. The overall arrangement and formation mode of the larval musculature appears very similar in both species, although only P. canadensis has a primary circular muscle posterior to the helicoid muscle. Muscle formation in the apical region of the embryo precedes that at the abapical pole and the primary longitudinal muscles form slightly later than the primary circular muscles. Myogenesis and larval myoanatomy appears highly conserved among polyclad flatworms, but differs significantly from that of other trochozoan clades. Our data suggest that the larval muscular ground pattern of polyclad larvae comprises a bodywall consisting of a helicoid muscle, circular and longitudinal muscles, several retractor muscles, and sphincter muscles around the stomodeum.     

A comparative study of motor patterns during pre-flight warm-up in hawkmoths

Summary Temporal patterns of activation of flight muscles were recorded by means of wires placed extracellularly in thoracic muscles. In the five species of hawkmoths studied, wingstrokes of small amplitude were produced during a preflight warm-up by synchronous contractions of certain groups of muscles which are antagonists in flight. The main depressor muscle, the dorsal longitudinal, was excited in synchrony with some or all of the indirect elevator muscles. Three direct muscles, the subalar, basalar and third axillary muscles, were usually excited out of phase with the dorsal longitudinal muscle. However, details of the motor pattern varied from species to species. During fixed flight phase changes comparable in magnitude to those which occur during the transition from warm-up to flight were observed in Manduca sexta and Smerinthus cerisyi. The results (summarized in Table 2) suggest that a variety of warm-up patterns evolved within the Sphingidae as modifications of a common mechanism generating flight motor patterns.I thank Dr. Harry Lange for assistance in the initial collecting of Manduca sexta and for identifying specimens of this species.     

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.     

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.     

Musculature of the penial complex: A new criterion in unravelling the phylogeny of Hygrophila (Gastropoda: Pulmonata)

The taxonomy of freshwater pulmonates (Hygrophila) has been in a fluid state warranting the search for new morphological criteria that may show congruence with molecular phylogenetic data. We examined the muscle arrangement in the penial complex (penis and penis sheath) of most major groups of freshwater pulmonates to explore to which extent the copulatory musculature can serve as a source of phylogenetic information for Hygrophila. The penises of Acroloxus lacustris (Acroloxidae), Radix auricularia (Lymnaeidae), and Physella acuta (Physidae) posses inner and outer layers of circular muscles and an intermediate layer of longitudinal muscles. The inner and outer muscle layers in the penis of Biomphalaria glabrata consist of circular muscles, but this species has two intermediate longitudinal layers separated by a lacunar space, which is crossed by radial and transverse fibers. The muscular wall of the penis of Planorbella duryi is composed of transverse and longitudinal fibers, with circular muscles as the outer layer. In Planorbidae, the penial musculature consists of inner and outer layers of longitudinal muscles and an intermediate layer of radial muscles. The penis sheath shows more variation in muscle patterns: its muscular wall has two layers in A. lacustris, P. acuta, and P. duryi, three layers in R. auricularia and Planorbinae and four layers in B. glabrata. To trace the evolution of the penial musculature, we mapped the muscle characters on a molecular phylogeny constructed from the concatenated 18S and mtCOI data set. The most convincing synapomorphies were found for Planorbinae (inner and outer penis layers of longitudinal muscles, three-layered wall of the penis sheath). A larger clade coinciding with Planorbidae is defined by the presence of radial muscles and two longitudinal layers in the penis. The comparative analysis of the penial musculature appears to be a promising tool in unraveling the phylogeny of Hygrophila.     

The pregenital abdominal musculature in phasmids and its implications for the basal phylogeny of Phasmatodea (Insecta: Polyneoptera)

Recently several conflicting hypotheses concerning the basal phylogenetic relationships within the Phasmatodea (stick and leaf insects) have emerged. In previous studies, musculature of the abdomen proved to be quite informative for identifying basal taxa among Phasmatodea and led to conclusions regarding the basal splitting events within the group. However, this character complex was not studied thoroughly for a representative number of species, and usually muscle innervation was omitted. In the present study the musculature and nerve topography of mid-abdominal segments in both sexes of seven phasmid species are described and compared in detail for the first time including all putative basal taxa, e.g. members of Timema, Agathemera, Phylliinae, Aschiphasmatinae and Heteropteryginae. The ground pattern of the muscle and nerve arrangement of mid-abdominal segments, i.e. of those not modified due to association with the thorax or genitalia, is reconstructed. In Timema, the inner ventral longitudinal muscles are present, whereas they are lost in all remaining Phasmatodea (Euphasmatodea). The ventral longitudinal muscles in the abdomen of Agathemera, which span the whole length of each segment, do not represent the plesiomorphic condition as previously assumed, but might be a result of secondary elongation of the external ventral longitudinal muscles. Sexual dimorphism, common within the Phasmatodea, also applies to the muscle arrangement in the abdomen of some species. Only in the females of Haaniella dehaanii (Heteropteryginae) and Phyllium celebicum (Phylliinae) the ventral external longitudinal muscles are elongated and span the length of the whole segment, possibly as a result of convergent evolution.     

Reconstruction of the musculature of <Emphasis Type="Italic">Magelona</Emphasis> cf. <Emphasis Type="Italic">mirabilis</Emphasis> (Magelonidae) and <Emphasis Type="Italic">Prionospio cirrifera</Emphasis> (Spionidae) (Polychaeta,Annelida) by phalloidin labeling and cLSM

Recent investigations have suggested that a lack of circular muscle fibers may be a common situation rather than a rare exception in polychaetes. As part of a comparative survey of polychaete muscle systems, the F-actin musculature subset of Magelona cf. mirabilis and Prionospio cirrifera were labeled with phalloidin and three-dimensionally analyzed and reconstructed by means of cLSM. Obvious similarities are sublongitudinal lateral, circumbuccal, palp retractor, dominating dorsal longitudinal, perpendicular lateral and ventral transverse muscles. Differences between M. cf. mirabilis and P. cirrifera are: (1) two types of prostomial muscles (transversal and longitudinal) in M. cf. mirabilis versus one type (diagonal) in P. cirrifera; (2) one type of palp muscles (longitudinal) in M. cf. mirabilis versus three types (longitudinal, diagonal, circular) in P. cirrifera; (3) five ventral longitudinal muscles (ventromedian, paramedian, ventral) in M. cf. mirabilis versus four (two paramedian, two ventral) in P. cirrifera. Ventral and lateral transverse fibers are present in the thorax, but absent in the abdomen of M. cf. mirabilis. The triangular lumen of the pharynx in M. cf. mirabilis is surrounded by radial muscle fibers; three sets of pharynx diductors attach to its dorsal side. The unique features of P. cirrifera are one pair of brain muscles and segmentally arranged dorsal transverse muscles, the latter located outside the longitudinal muscles. The transverse lateral muscles are restricted to the sides and lie beneath the longitudinal muscles, a pattern described here for the first time. A true, outer layer of circular fibers is absent in both species of Spionida that were investigated.     

Jaw muscle fiber type distribution in Hawaiian gobioid stream fishes: histochemical correlations with feeding ecology and behavior

Differences in fiber type distribution in the axial muscles of Hawaiian gobioid stream fishes have previously been linked to differences in locomotor performance, behavior, and diet across species. Using ATPase assays, we examined fiber types of the jaw opening sternohyoideus muscle across five species, as well as fiber types of three jaw closing muscles (adductor mandibulae A1, A2, and A3). The jaw muscles of some species of Hawaiian stream gobies contained substantial red fiber components. Some jaw muscles always had greater proportions of white muscle fibers than other jaw muscles, independent of species. In addition, comparing across species, the dietary generalists (Awaous guamensis and Stenogobius hawaiiensis) had a lower proportion of white muscle fibers in all jaw muscles than the dietary specialists (Lentipes concolor, Sicyopterus stimpsoni, and Eleotris sandwicensis). Among Hawaiian stream gobies, generalist diets may favor a wider range of muscle performance, provided by a mix of white and red muscle fibers, than is typical of dietary specialists, which may have a higher proportion of fast-twitch white fibers in jaw muscles to help meet the demands of rapid predatory strikes or feeding in fast-flowing habitats.     

The musculature of Draculiciteria tessalata (Chaetonotida, Paucitubulatina): implications for the evolution of dorsoventral muscles in Gastrotricha

The muscular system of the marine interstitial gastrotrich Draculiciteria tessalata (Chaetonotida, Paucitubulatina) was analyzed with fluorescent phalloidin. Muscles in circular, longitudinal, helicoidal and dorsoventral orientations were found. Circular muscles were present as discreet rings on the pharynx only. Five pairs of longitudinal muscles were found in dorsal, lateral and ventral positions. One of the two pairs of lateral muscles is newly described for the species. Helicoidal muscles, external to the circular muscles and some longitudinal bands, spiraled around the pharynx and anterior portion of the intestine. Two pairs of segmentally-arranged dorsoventral muscles were also present. Lateral dorsoventral muscles extended from the base of the pharynx to the anterior part of the caudal furca. Medial dorsoventral muscles extended from the pharyngeal-intestinal junction into each ramus of the caudal furca. A hypothesis on the evolution of dorsoventral muscles in D. tessalata is proposed which includes a splitting of circular muscles into separate somatic and splanchnic components with a further displacement of both muscle sets into a dorsoventral orientation.     

Development and embryonic pattern of body wall musculature in the crassiclitellate Eisenia andrei (Annelida,Clitellata)

During early development of Eisenia andrei (Crassiclitellata), a loose arrangement of primary circular and longitudinal muscles encloses the whole embryo. Circular muscles differentiate in an anterior–posterior progression creating a segmental pattern. Primary circular muscles emerge at the segmental borders while later in development the central part of each segment is filled with circular strands. Longitudinal muscles develop in an anterio‐posterior manner as well, but by continuous lengthening. Muscle growth is not restricted by segmental boundaries. The development begins with one pair of prominent longitudinal muscles differentiating ventrally along the right and the left germ band. These first muscles provide a guiding structure for the parallel organization of the afterwards differentiating longitudinal musculature. Additional primary longitudinal muscles emerge and form, together with the initial circular muscles, the primary muscle grid of the embryo. During the following development, secondary longitudinal muscle strands develop and integrate themselves into the primary grid. Meanwhile the primary circular muscles split into thin strands in a ventral to dorsal progression. Thus, a fine structured mesh of circular and longitudinal muscles is generated. Compared to other “Oligochaeta”, embryonic muscle patterns in E. andrei are adapted to the development of a lecithotrophic embryo. Nevertheless, two general characteristics of annelid muscle development become evident. The first is the segmental development of the circular muscles from a set of initial muscles situated at the segment borders. Second, there is a continuous development of primary longitudinal muscles starting at the anterior pole. At least one pair of main primary longitudinal strands is characteristic in Annelida. The space between all primary strands is filled with secondary longitudinal strands during further development. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Musculature in polychaetes: comparison of Myrianida prolifera (Syllidae) and Sphaerodoropsis sp. (Sphaerodoridae)

Abstract. The relationship of the polychaete taxa Syllidae and Sphaerodoridae within Phyllodocida is still unresolved: phylogenetic analyses either show them as sister groups or more widely separated. The present article aims to provide information about the structure of the muscular system that could be essential for understanding their relationship. A crucial point is whether the body wall contains circular muscles, which has recently been shown to be absent in more taxa than previously known. The F-actin filaments in members of Myrianida prolifera (Syllidae) and Sphaerodoropsis sp. (Sphaerodoridae) were labeled with phalloidin and their three-dimensional relationships reconstructed by means of confocal laser scanning microscopy. Among the noteworthy differences that emerged between the species are (1) members of M. prolifera possess four, those of Sphaerodoropsis sp. eight, longitudinal muscle strands; (2) the body wall in M. prolifera contains transverse fibers in a typical, supralongitudinal position, while in Sphaerodoropsis sp., corresponding fibers lie beneath the longitudinal strands; (3) pro- and peristomium in M. prolifera have no distinct F-actin fibers, while five longitudinal pairs and three single transverse muscular fibers shape the anterior end in Sphaerodoropsis sp.; (4) the proventricle of M. prolifera comprises primarily radial muscle fibers arranged in distinct rows, while in Sphaerodoropsis sp. the axial proboscis consists of longitudinal and circular fibers and radial fibers are lacking; (5) in M. prolifera, the proximal and distal sections of the two anteriormost pairs of dorsal cirri possess longitudinal myofilaments, which are separate from the body wall musculature; by contrast, all appendages in Sphaerodoropsis sp. do not; (6) both species have bracing muscles: in M. prolifera they are positioned above the longitudinal fibers, whereas in Sphaerodoropsis sp. they are uniquely positioned between longitudinal and sublongitudinal transverse fibers. These results do not support a sister-group relationship of Syllidae and Sphaerodoridae. In addition, Sphaerodoropsis sp. is yet another example in the list of polychaetes lacking typical circular muscles in the body wall.     

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.     

Evolutionary aspects of pattern formation during clitellate muscle development

As a taxon of the lophotrochozoans, annelids have re-entered scientific investigations focusing on plesiomorphic bilaterian features and the evolutionary changes therein. The view of a clitellate-like plesiomorphic muscle arrangement in annelids has been challenged by recent investigations of polychaete muscle organization. However, there are few investigations of muscle formation in clitellate species that address this problem. Direct comparison of potential homologous muscles between these annelid groups is thus hampered. Somatic muscle formation during embryogenesis of two clitellates-the oligochaete Limnodrilus sp. and the hirudinean Erpobdella octoculata-occurs by distinct processes in each species, even though they share a closed outer layer of circular and an inner layer of longitudinal muscles characteristic of clitellates. In E. octoculata, the first emerging longitudinal muscles are distributed irregularly on the body surface of the embryo whereas the circular muscles appear in an orderly repetitive pattern along the anterioposterior axis. Both primary muscle types consist of fiber-bundles that branch at both their ends. This way the circular muscle bundles divide into a fine muscle-grid. The primary longitudinal muscles are incorporated into a second type of longitudinal muscles, the latter starting to differentiate adjacent to the ventral nerve cord. Those secondary muscles emerge in a ventral to dorsal manner, enclosing the embryo of E. octoculata. In Limnodrilus sp., one dorsal and one ventral bilateral pair of primary longitudinal muscles are established initially, elongating toward posterior. Initial circular muscles are emerging in a segmental pattern. Both muscle layers are completed later in development by the addition of secondary longitudinal and circular muscles. Some features of embryonic longitudinal muscle patterns in Limnodrilus sp. are comparable to structures found in adult polychaete muscle systems. Our findings show that comparative studies of body-wall muscle formation during clitellate embryogenesis are a promising approach to gain further information on annelid muscle arrangements.     

Ultrastructure of the subepidermal musculature of Xenoturbella bocki, the adelphotaxon of the Bilateria

 Xenoturbella bocki is the only species of the high-ranked taxon Xenoturbellida. The species lives on marine mud bottoms at a depth of 20–120 m and moves extremely slowly by ciliary gliding. Nevertheless it possesses a well-developed body wall musculature with outer circular muscles, a prominent layer of inner longitudinal muscles and radial muscles that extend from the outer circular myocytes to the musculature surrounding the gastrodermis. The longitudinal myocytes are not compact cells, but form fascicles of fibrils running parallel to each other. Fine cytoplasmic cords connect the fibres of a cell to each other and with its nuclear region. The muscles are embedded within a sometimes expansive extracellular matrix (ECM) that lacks any fibrillar components. All muscle cells display conspicuous and numerous cytoplasmic extensions that are intermingled with each other. Tight coupling between adjacent cell membranes is not found, but zonula adhaerens-like junctions exist. Fibrils belonging to different myocytes, but also fibrils of the same cell, are coupled by such cytoplasmic extensions. Circular, radial and at least the peripheral longitudinal myocytes display cell-matrix connections with the internal lamina, a component of the subepidermal ECM. This internal lamina projects down into the centres of the fascicles with longitudinal muscle fibrils and forms extensive attachment zones with the muscle cells, reminiscent of focal contacts. For the ingestion of food, X. bocki opens the simple mouth pore and protrudes the aciliated gastrodermis. The body wall musculature is responsible for this protrusion and also for the withdrawal of the gastrodermis. In the past, possible phylogenetic kinships with the Acoelomorpha (Plathelminthes) or the Enteropneusta and Holothuroidea were discussed, but, on the basis of all information available, X. bocki is hypothesized to be the sister taxon of the Bilateria. Accepted: 2 April 1997     

The musculature of three species of gastrotrichs surveyed with confocal laser scanning microscopy (CLSM)

The muscular system of gastrotrichs consists of circular, longitudinal and helicoidal bands that when analysed with confocal laser scanning microscopy, provide new insights into their functional organization and phylogenetic importance. We therefore undertook a comparative study of the muscle organization in three species of Gastrotricha from the orders Macrodasyida (Paradasys sp., Lepidodasyidae; Turbanella sp., Turbanellidae) and Chaetonotida (Polymerurus nodicaudus, Chaetonotidae). The general muscle organization of the marine interstitial macrodasyidans, Paradasys and Turbanella, not only confirms earlier observation on other species but also adds new details concerning the organization and number of helicoidal, longitudinal and other muscle bands (e.g. semicircular band). The freshwater, epibenthic–epiphytic chaetonotid, Polymerurus nodicaudus, has a similar muscular organization to other species of Chaetonotidae, especially species of Chaetonotus, Halichaetonotus and Lepidodermella. Perhaps unique to Polymerurus is the combined presence of an unbranched Rückenhautmuskel (also in Halichaetonotus and Lepidodermella) and a specialized dorsoventral caudal muscle, which flank the splanchnic component of the longitudinal muscles (only in Chaetonotus and Lepidodermella). This combination, together with the presence of splanchnic dorsoventral muscles, known only in Xenotrichulidae, implies a unique phylogenetic position for Polymerurus, and indicates a potential basal position of this taxon among the Chaetonotidae studied so far (i.e. Aspidiophorus, Chaetonotus, Halichaetonotus and Lepidodermella).     

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.     

Motor supply of the dorsal longitudinal muscles II: Comparison of motoneurone sets in Tracheata

The set of motoneurones (MNs) supplying a specific ensemble of dorsal longitudinal muscles was studied in several segments of a primarily apterygote insect, Lepisma saccharina (Zygentoma), and a centipede, Lithobius forficatus (Chilopoda). In all preparations, a distribution of the MNs in two adjacent ganglia is observed. The cell number and their morphology in the thorax of L. saccharina are similar to the equivalent neural system of two Caelifera species, whereas in the L. saccharina abdomen there is some reduction in cell number. It appears that for both dicondylean insect groups homologous MNs exist. For L. forficatus, 12 MNs are present in the anterior ganglion and 4 in the posterior one. The morphology of these neurones is different compared to the insect MNs supplying an apparently equivalent set of muscles. Additionally, the neural supply of the intersegmental dorsoventral muscle was studied in Schistocerca gregaria, L. saccharina and L. forficatus. Both insect species show a pronounced similarity of the MN set. Again, the neural set in L. forficatus is different from that of the Dicondylia. Our results support the idea that the structure of MNs in the largest present taxon of Insecta, the Dicondylia, is conserved irrespective of crucial changes in the periphery (e.g. primarily apterygote vs oterygote). The muscles and their neurones are probably part of a basic neuromuscular ground pattern. The pronounced differences in a centipede are discussed in phylogenetic terms.Abbreviations DLM dorsal longitudinal muscle - DUM dorsal unpaired median - ISM intersegmental dorsoventral muscle - MN motoneurone - M muscle (number) - N nerve (number)     

The muscular system of Dactylopodola baltica and other macrodasyidan gastrotrichs in a functional and phylogenetic perspective

The gastrotrich muscular system is characterized by band-like muscles arranged in orientations that reflect both function and phylogeny. To better understand the evolution of the Dactylopodolidae, a putative primitive lineage and potential sister group to other extant macrodasyidans, we have used a fluorescent phalloidin stain to visualize muscle patterns in the marine gastrotrich Dactylopodola baltica and eight other species of Macrodasyida from four families. The musculature of D. baltica is arranged as a series of circular, helicoidal and longitudinal bands around the digestive tract. Circular muscles and longitudinal muscles were found in splanchnic and somatic positions. Helicoidal muscles, in 50–60° angles with respect to the longitudinal body axis, surrounded circular and longitudinal splanchnic muscles in a spiralling orientation. The largest longitudinal muscles were the ventrolateral bands composed of numerous cross-striated myocytes arranged in parallel arrays. The overall arrangement of the muscular system of D. baltica showed several similarities to other macrodasyidan gastrotrichs, including the presence and location of circular, helicoidal and longitudinal muscles, their orientation with respect to the longitudinal body axis and their points of insertion. Unique to D. baltica is the anterior and posterior arrangement of the ventrolateral muscles and the orientation of muscle branches that supply the ventral and dorsal aspects of the pharynx. Muscle data from observations of D. baltica and eight additional species were coded as phylogenetic characters, mapped onto a cladogram and compared to an existing phylogeny of the order. The direction of evolutionary change in specific muscle groups was inferred, as was the ground pattern of muscles for the Macrodasyida.     

Catecholaminergic innervation of muscles in the hindgut of crustaceans

Summary The crustacean species Pacifastacus leniusculus and Gammarus pulex were investigated by electron microscopy in a search for possible neuromuscular junctions in the hindgut, which has a rich supply of catecholaminergic fibres. True neuromuscular synapses were found in both species between nerve terminals containing dense-core vesicles (80–110 nm in diam.) and muscle fibres. We suggest that the dense-core vesicle terminals contain a catecholamine, and this is supported by ultrahistochemical tests for monoamines. Two types of junctions are found: one in which the nerve terminal is embedded in the muscle cell (both species) and one in which protrusions from the muscle cell meet nerve terminals (Pacifastacus). Gammarus pulex, which has only circular muscles in the hindgut, has only catecholaminergic innervation, whereas Pacifastacus leniusculus has circular and longitudinal muscles both with at least two types of innervation.The investigation was supported by grants from the Swedish Natural Science Research Council (B 2760-009), the Hungarian Academy of Sciences, the Royal Swedish Academy of Sciences, and the Magnus Bergvall Foundation. We are also indebted to Mrs. Lena Sandell for her skilful technical assistance