Neural mechanism for generating and switching motor patterns of rhythmic movements of ovipositor valves in the cricket

In adult female crickets (Gryllus bimaculatus), rhythmic movements of ovipositor valves are produced by contractions of a set of ovipositor muscles that mediate egg-laying behavior. Recordings from implanted wire electrodes in the ovipositor muscles of freely moving crickets revealed sequential changes in the temporal pattern of motor activity that corresponded to shifts between behavioral steps: penetration of the ovipositor into a substrate, deposition of eggs, and withdrawal of the ovipositor from the substrate. We aimed in this study to illustrate the neuronal organization producing these motor patterns and the pattern-switching mechanism during the behavioral sequence. Firstly, we obtained intracellular recordings in tethered preparations, and identified 12 types of interneurons that were involved in the rhythmic activity of the ovipositor muscles. These interneurons fell into two classes: ‘initiator interneurons’ in which excitation preceded the rhythmic contractions of ovipositor muscles, and ‘oscillator interneurons’ in which the rhythmic oscillation and spike bursting occurred in sync with the oviposition motor rhythm. One of the oscillator interneurons exhibited different depolarization patterns in the penetration and deposition motor rhythms. It is likely that some of the oscillator interneurons are involved in producing different oviposition motor patterns. Secondly, we analyzed oviposition motor patterns when the mecahnosensory hairs located on the inside surface of the dorsal ovipositor valves were removed. In deafferented preparations, the sequential change from deposition to withdrawal did not occur. Therefore, the switching from deposition pattern to withdrawal pattern is signaled by the hair sensilla that detect the passage of an egg just before it is expelled.     

Structure of female genitalia of glassy-winged sharpshooter, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae)

The functional reproductive morphology of the female glassy-winged sharpshooter, Homalodisca coagulata (Say), is described at both light microscopy and scanning electron microscopy levels. The female has nine abdominal segments; the seventh to the ninth abdominal segments are modified for reproduction; the eighth tergite is reduced to two segments, with the ovipositor partially exposed from the modified ninth segment-the pygofer. The pygofer, covered with trichoid and coeloconic sensilla, almost completely encloses the ovipositor, which consists of three pairs of valvulae and two pairs of valvifers. The first and second valvulae function together for oviposition. The first valvulae are located exterior to the second valvulae, both of which bear many trichoid, campaniform, and coeloconic sensilla. The third valvulae, possessing many coeloconic sensilla, envelope the first and second valvulae. Seven major muscles are found to be associated with the ovipositor and the pygofer. The oviposition process is described with respect to the activity of the valvulae and their associated musculature. The female morphology follows the general pattern of cicadellids as a group.     

Abdominal muscle use during quiet breathing and hyperpnea in uninformed subjects

Although there is electromyographic evidence for abdominal muscle activity during quiet breathing in standing subjects, several studies have shown, or assumed, that subjects normally breathe on their relaxation characteristics. This latter observation would by itself suggest that abdominal muscles do not contract during quiet breathing. To test this assumption we observed abdominal and rib cage displacements with magnetometers in 17 uninformed subjects. During quiet breathing most subjects showed evidence of tonic or phasic abdominal muscle contraction while standing and sitting but not supine. Subjects studied during hyperpnea immediately following exercise-showed evidence of greater abdominal muscle contraction than at rest. We conclude that most subjects standing at rest normally contract their abdominal muscles.     

Skeletomuscular development of genital segments in the dragonfly Anax imperator (Odonata, Aeshnidae) during metamorphosis and its implications for the evolutionary morphology of the insect ovipositor

The skeleton-muscular organisation of abdominal segments 7-9 in female Anax imperator L. (Anisoptera, Aeshnidae) was examined in the stages of ultimate larva, teneral imago, and mature imago, with special emphasis on the transformation of the muscle arrangement. The absence of certain muscles in the genital segments compared to the 7th pre-genital segment was noted on all studied stages. Reductions of certain muscles in adults compared to those in larvae are reported. Some of ovipositor's muscles appear already in larvae. Attachment sites of larval muscles are retained in freshly emerged females concurrently with integument transformations. This situation allows for precise determination of the borders of newly differentiated genital sclerites and, therefore, of the possible origin of certain ovipositor elements in odonates. All changes in the segmental sets of studied abdominal muscles during metamorphosis are tabulated, and displacements of muscles are documented and illustrated. Schematic figures illustrating homologies between the parts of larval and imaginal abdominal sclerites are provided. The origins of the components of the endophytic ovipositor in Odonata as well as their implications for the evolutionary morphology of the insect ovipositor are discussed.     

Seasonal change in the spatial utilization of host mussels in relation to ovipositor length by female rosy bitterling Rhodeus ocellatus kurumeus

The seasonal changes in ovipositor length and utilization patterns of mussels for oviposition in the rosy bitterling Rhodeus ocellatus kurumeus (Cyprinidae) were investigated in a field experiment and field surveys during the breeding period (April to August). The mean length of ovipositors at oviposition was short at the start (early April) and end (July) of the breeding period. Females with long ovipositor at oviposition were collected between mid‐April and June. Mark‐and‐recapture data showed that ovipositor length at oviposition changed rhythmically throughout the breeding period, shortening and lengthening as the female entered the spawning and resting phase. The density of rosy bitterling embryos in mussels increased between April and June, peaking in May, but decreasing in July. The position of eggs on mussel gills varied from close to the exhalant siphon to deeper inside the gill during April, and periodically thereafter. There was a positive correlation between ovipositor length at oviposition and the distance from exhalant siphon of mussels to eggs deposited by females, suggesting that ovipositor length at oviposition determined the position of eggs deposited on a mussel gill. Because dissolved oxygen in mussel gills decreased with the density of bitterling embryos, suitable positions for embryo survival in gills changed with embryo density. By changing ovipositor length at oviposition, females might be able to spawn their eggs in a position that maximizes embryo survival. Thus, plasticity in ovipositor length at oviposition may play an important role as an adaptation of rosy bitterling in utilizing mussels when their quality as a spawning substratum fluctuates seasonally.     

Unusual tension reception in an insect

Muscle tension receptors in animals monitor the tension generated by muscles. This information is important for the initiation and control of movements and for muscle tone in relation to spatial orientation and gravity. Vertebrates have tendon organs located at the musculo-tendinous junction. The number of muscle fibers attached to one receptor is in the range of 3 to 25. In insects by contrast, only a few examples are known where muscle tension is measured by only single receptors embedded in the muscle. All other muscle activity is monitored by a range of other receptors that detect strains on the cuticle or movements of the joints. Here we describe a set of approximately 200 receptor cells located on a single insect muscle. These receptor cells are associated with ovipositor muscle fibers and were preferentially responsive to muscle tension and not muscle length. Although single receptors may respond differently, their summed response to altered muscle tension characterized them as phasic-tonic type receptors. Experimental activation of muscle receptors in animals producing a basic oviposition motor pattern inhibited homonymous muscle activity without resetting the phase of the rhythm. These results suggest a potential role of tension receptors in regulating ovipositor muscle activity and in particular preventing excessive muscle tension during oviposition. The muscle receptors presented here provide the first example of tension measurement in insects by a few hundred receptor cells associated with a single muscle. Their role in motor control and relation to other tension receptors in vertebrates and invertebrates are discussed.     

Importance of plant physical cues in host acceptance for oviposition by Busseola fusca

Plant and surrogate stems exhibiting specific combinations of physical cues were used to determine which plant‐related stimuli influence the oviposition of Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The number of eggs and egg batches laid per female increased with an increase in diameter of both natural and artificial stems. Direct observations of the oviposition behaviour (walking, antennating, and sweeping with the ovipositor) indicated that the female moths preferred oviposition supports with a large diameter and non‐pubescent or smooth surfaces over pubescent or rough ones. Pubescence and rough surfaces significantly affected the behavioural steps leading to oviposition by interfering with the ovipositor sweep process necessary to find a suitable oviposition site. Furthermore, more eggs and egg batches were laid on soft than rigid supports. The rigidity of the support affected the proper insertion of the ovipositor for egg deposition. Our results underline the importance of physical stimuli in B. fusca's choice of an oviposition site, which may facilitate the identification of potential host plants or preferred oviposition sites on a plant for this species.     

Functional anatomy of the vagina muscles in the adult western conifer seed bug,Leptoglossus occidentalis (Heteroptera: Coreidae), and its implication for the egg laying behaviour in insects

The anatomy of the female reproductive tract and the nerve-evoked contractions of the vagina muscles and their association with the ovipositor in the western conifer seed bug, Leptoglossus occidentalis (Heidemann) are investigated for the first time. The reproductive tract consists of a set of paired telotrophic ovaries, each containing seven ovarioles, located in the anterior lateral regions of the abdomen. Each ovary is attached to a lateral oviduct which spans most of the abdomen to attach to a relatively short common oviduct that joins the vagina near the rear of the animal. The vagina is associated with a pair of bilaterally symmetrical muscles attached at their posterior ends to lateral extensions of sternite VIII, the valvifer of the Type II ovipositor. From this attachment site, the muscles fan out medially and anteriorly to converge along the dorsal midline of the vagina up to the base of the common oviduct. Vagina muscles respond to a single stimulation of their motor nerves by producing a smooth contraction lasting approximately 1 s. With increasing frequencies of stimulation, the muscle contractions summate to create a tetanic response. The muscles are fatigue resistant being able to maintain the same degree of tension for up to 10 min at 10 Hz stimulation. Visual observation shows that other muscles associated with the valves of the ovipositor behave in a similar fashion to that of the vagina muscles from which the tension recordings were obtained. Fatigue-resistant vagina muscles are discussed in relation to copulation, sperm transport and this insect's ability to deposit a series of eggs directly onto the surface of a conifer needle in a manner by which eight or more blunt-ended eggs are packed end-to-end in a single row.     

A Neuro-Mechanical Model of a Single Leg Joint Highlighting the Basic Physiological Role of Fast and Slow Muscle Fibres of an Insect Muscle System

In legged animals, the muscle system has a dual function: to produce forces and torques necessary to move the limbs in a systematic way, and to maintain the body in a static position. These two functions are performed by the contribution of specialized motor units, i.e. motoneurons driving sets of specialized muscle fibres. With reference to their overall contraction and metabolic properties they are called fast and slow muscle fibres and can be found ubiquitously in skeletal muscles. Both fibre types are active during stepping, but only the slow ones maintain the posture of the body. From these findings, the general hypothesis on a functional segregation between both fibre types and their neuronal control has arisen. Earlier muscle models did not fully take this aspect into account. They either focused on certain aspects of muscular function or were developed to describe specific behaviours only. By contrast, our neuro-mechanical model is more general as it allows functionally to differentiate between static and dynamic aspects of movement control. It does so by including both muscle fibre types and separate motoneuron drives. Our model helps to gain a deeper insight into how the nervous system might combine neuronal control of locomotion and posture. It predicts that (1) positioning the leg at a specific retraction angle in steady state is most likely due to the extent of recruitment of slow muscle fibres and not to the force developed in the individual fibres of the antagonistic muscles; (2) the fast muscle fibres of antagonistic muscles contract alternately during stepping, while co-contraction of the slow muscle fibres takes place during steady state; (3) there are several possible ways of transition between movement and steady state of the leg achieved by varying the time course of recruitment of the fibres in the participating muscles.     

Ecological aspects of the external morphology and functionality of the psychomyiid female ovipositor (Insecta,Trichoptera)

Females of most psychomyiid species bear an elongated ovipositor enabling them to oviposit their eggs into grooves and cavities in different kinds of substrates in freshwaters. Although the preference of psychomyiid species for oviposition into distinct substrates and the subsequent larval life performance in aquatic habitats is already known, the mode of oviposition and the functional morphology of the elongated ovipositor have not been described until now. In this study we present SEM photographs of some psychomyiid species with female ovipositors of different lengths and shapes, explaining their preference for oviposition into distinct substrates. Additionally, we discuss some ecological aspects of the ovipositor shapes and the mode of egg laying for psychomyiids. The female ovipositor consists of two body segments, with an elongated IXth and a distinctly shorter Xth segment, which is flexible and can be pushed up dorsally when releasing the eggs. On the basis of SEM photographs, we suppose that the opening of the channel through which the eggs were released is located ventrally near the ovipositor tip. The ovipositor itself is characterised by a ventral cleft reaching from the gonoporus of segment IX to the tip of the last segment X. We stored adult females abdomina overnight in different aqueous dilutions of ethanol leading to different stages of swelling of the ovipositors (grade of swelling in distilled water >30% ethanol >70% ethanol). Some internal membrane-like structures, normally infolded into the ovipositor, became visible by the swelling of the ovipositor. We discuss the possible rearrangement of the organisation of segment IX resulting in the development of an ovipositor on the basis of SEM photographs of the differently swollen ovipositors.     

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.     

Origin and development of unusual insect muscle tension receptors

This work describes the origin and development of about 200 tension receptor cells located around the anterior attachment site of the locust ovipositor muscle and their migration to their final position on the muscle fibres. The locust ovipositor muscle is the only insect system in which more than 100 tension receptor cells are associated with a single muscle. Neuronal precursors of tension receptors are first detectable by horseradish peroxidase immunohistochemistry in fourth instar larvae. Precursors consist of cell clusters (doublets, triplets and quadruplets) located on the anterior attachment site of the muscle. In the early fifth larval stage, cell clusters are absent, although a few sensory neurons that lie embedded between the muscle fibres are apparent. These neurons send their dendrites towards the anterior end of the muscle fibres and their axons posteriorly. By the fourth day of the fifth larval stage, a large number of cell clusters appears on the anterior muscle attachment site. In addition to these assemblies, cells have been identified that extend long processes running exactly along the lateral margin of the attachment site. These cells are thought to provide navigating cues for migrating tension receptors, since they are absent in later stages. By the end of the fifth larval stage, most of the clusters gradually disappear and increasing numbers of differentiated neurons embedded between the muscle fibres become visible. We conclude that the majority of tension receptors develop during the last larval stage from precursors situated on the muscle apodeme. They then migrate from the apodeme to their final place on the muscle fibres where they assume an appropriate orientation.     

The number of sarcomeres and architecture of the M. gastrocnemius of the rat

The aim of this study was to investigate the number of sarcomeres of different regions (proximal, intermediate and distal third) of the M. gastrocnemius of the rat and compare them with in vivo measurements of the length of the most proximal and distal muscle bundles. These lengths were measured with the aid of dividers at the muscle resting length. The number of sarcomeres was calculated from the length of fibres (measured at 20 times enlargement) tested from HNO3-treated muscle and the average sarcomere length (determined from 80 microns samples taken along the fibres every 800 microns). Ten fibres were isolated from each of three regions of six muscles. All muscles showed the smallest number of sarcomeres in the proximal region of the muscle and increasingly higher numbers in the intermediate and distal parts. The number of sarcomeres in the proximal region is significantly (p less than 0.01) smaller than that of the distal region. These results agree with the results of in vivo length measurements of the most proximal and distal bundles (resp. 31 and 36% of the muscle resting length), the former being significantly (p less than .01) smaller. As there is no significant difference (p less than 0.01) in the length of the treated fibres of the three regions it is concluded that HNO3 treatment does affect the fibres of the muscle in the different regions in a non uniform fashion.     

Host-handling behavior of the parasitoid,Diglyphus minoeus [Hym.: Eulophidae], parasitizing the honeysuckle leaf-miner,Phytomyza lonicerae [Dipt.: Agromyzidae]

The host-handling behavior of individual female waspsDiglyphys minoeus which attack the larvae of the honeysuckle leaf-miner,Phytomyza lonicerae, include 4 types of behavior: probing, ovipositor insertion, host-feeding, and resting. Ovipositor insertion may either be injection of venom, probing of the host by the sensilla on the ovipositor's tip or egg laying. Three types of attacks were distinguished: oviposition attack for unparasitized larvae, host-feeding attack for unparasitized host larvae and host rejection for previously parasitized host larvae. Oviposition attack was characterized by frequent alternation between probing and ovipositor insertion, long duration of ovipositor insertion and resting, and the long duration of host-handling. Resting behavior is thought to protect the progeny against superparasitism, host-feeding by other wasps or hosts' recovery from paralysis. Host-feeding attack was characterized by frequent alternation between host-feeding and ovipositor insertion and long duration of host-feeding. Host rejection was composed mainly of probing and ovipositor insertion and short handling time.      

On a phenomenological model for fatigue effects in skeletal muscles

This work deals with the development and implementation of a new fatigue model for simulating fatigue effects in skeletal muscles. Basic idea of this modelling strategy is an approach that divides the fibres of a muscle into three groups: fibres in the active state, those that are already fatigued and fibres in the resting state. All fibres are able to switch between the different groups by defining adequate rates. In this way a continuous transfer of fibres between those three states has been described. Rooted on an incompressible, hyperelastic constitutive law with transversely isotropic characteristics the fatigue model has been implemented in the framework of the finite element method. Numerical examples are given in order to illustrate the ability of this model. Further, we validate the model by fatigue experiments of the rat soleus muscle. In doing so, it proves that the model is able to predict physiological observations and mechanical test results.     

Isolation of the abdomen releases oviposition behaviour in females of the cricket, Acheta domesticus

Upon isolation, abdomens of adult female house crickets (Acheta domesticus) produced abdominal and ovipositor movements characteristic of normal oviposition. Oviposition behaviour was thus released even in reproductively mature or immature virgins where under normal conditions it was never observed. Decapitation was not sufficient to release oviposition behaviour but transection of the ventral nerve cord between the thorax and the abdomen of immobilized females evoked the response. These observations indicate that the motor programmes for certain components of the oviposition sequence reside in the abdominal ganglia. Moreover, the prerequisite circuitry for ovipositional posturing of the abdomen and ovipositor appears to be functional prior to sexual maturity and insemination, primed by mating, and subject to inhibition by the thoracic ganglia.     

Musculature of the ovipositor of <Emphasis Type="Italic">Oxyna parietina</Emphasis> (Linnaeus, 1758) (Diptera,Tephritidae) and its relation to the larval habits

The structure of the ovipositor sclerites and muscles was studied in the tephritid fly Oxyna parietina (Linnaeus, 1758) inducing galls on the stems of Artemisia vulgaris. Adaptations of the ovipositor structure associated with changes of the oviposition substrate due to new larval habits are analyzed. The ovipositor muscles of Oxyna parietina are compared to those of Campiglossa. The genera Oxyna Robineau-Desvoidy, 1830 and Campiglossa Rondani, 1870 belong to the same genus-group of Tephritini, but differ in their host associations and oviposition habits: the larvae of Campiglossa plantaginis (Haliday, 1833) develop in the capitula of Aster tripolium and other asters (Asteraceae). The ovipositor sclerites and muscles are similar in the two genera. Progression of hemolymph into the membranous sheath of the ovipositor and protraction of the aculeus are necessary conditions for laying eggs into the capitula of Asteraceae (Campiglossa plantaginis), as well as for insertion of eggs into the axils of Artemisia leaves (Oxyna parietina). The most significant characters of Oxyna and Campiglossa include the presence of the hyaline apodeme and associated muscles MVM 6 and MVM 7 (instead of the median apodeme in Urophora). Thus, in other tephritid flies similarity in the structure of the ovipositor muscles may reflect similar morphofunctional adaptations to laying eggs into similar substrates, but similarity of Campiglossa and Oxyna in the structure of the ovipositor muscles is due to their close relations.     

Peculiarities of muscles and skeleton structure in <Emphasis Type="Italic">Campiglossa plantaginis</Emphasis> (Haliday, 1833) ovipositor (Diptera,Terthritidae) in association with larval mode of life

Sclerites and muscles of the ovipositor in the tephritid fly Campiglossa plantaginis (Haliday, 1833), with phytophagous larvae developing in inflorescences of Aster tripolium L. and other Asteraceae, were examined. Structural adaptations of the ovipositor, providing oviposition into different substrates, are discussed in relation to different trophic specialization of larvae.     

Host location and oviposition in a basal group of parasitic wasps: the subgenual organ, ovipositor apparatus and associated structures in the Orussidae (Hymenoptera, Insecta)

Anatomical studies and behavioural observations indicate that representatives of the Orussidae use vibrational sounding to detect suitable oviposition sites. During host location, vibrations generated by tapping the tips of the antennae against the wood are picked up by the fore legs through the basitarsal spurs, transmitted along the basitarsi to thin-walled areas on the tibiae and through haemolymph to the subgenual organs, where they are transduced into nerve impulses. The apical antennomeres are distinctly shaped and have the cuticle thickened distally. The fore basitarsi have weakly sclerotised basitarsal lines proximally and membranous basitarsal spurs distally. The external wall of the fore tibiae have thin-walled areas distally on their posterior parts. Internally, large subgenual organs are situated opposite the thin-walled areas and each organ consists of 300–400 scolopidial units suspended between a lateral cuticular spine, a ventral sheet and a median ridge. The ovipositor is several times the length of the body of the wasp. When at rest, it extends all the way into the prothorax, where it is coiled before extending posteriorly to lie between the third valvulae distally. The ovipositor lies in a membranous ovipositor sac attached posteriorly to the proximal parts of the ovipositor apparatus and the posterior margin of sternum 7. In the ovipositor apparatus, the anterior parts of the second valvifers are displaced and expanded anterodorsally, inverting the first valvifers and the base of the ovipositor. When in use, the ovipositor is extended and retracted by median apodemes situated on the anterior margins of abdominal sterna 3–7. Longitudinal muscles between the apodemes allow the latter to grip the ovipositor in troughs between them. The ovipositor extends from the abdomen at the tip of sternum 7, and an internal trough on sternum 7 serves to guide the ovipositor into the wood. Despite the alterations observed in the ovipositor apparatus in the Orussidae, the musculature is almost complete and the mode of operation presumably not much different from that of other representatives of the Hymenoptera. The different ways parasitic wasps with very long ovipositors handle and accommodate these and the implications for the evolutionary history of Hymenoptera are discussed. Accepted: 14 March 2001     

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.