The ptychoid defensive mechanism in Euphthiracaroidea (Acari: Oribatida): A comparison of muscular elements with functional considerations

Ptychoidy is a mechanical predator defence in some groups of Oribatida (Acari), where the animals can retract their legs into the idiosoma and encapsulate. This mechanism is enabled by a number of morphological adaptations. We used the non-invasive technique of synchrotron X-ray microtomography to compare muscular elements involved in ptychoidy of two species from the Euphthiracaroidea (Oribotritia banksi and Rhysotritia ardua) which differ in a number of cuticular elements involved in ptychoidy. We hypothesize that a strong functional correlation exists between these cuticular structures and their corresponding musculature. We found a number of distinct differences concerning quantitative and qualitative muscle morphology. For testing the functional impact of different muscle configurations we simulated two conditions in silico (encapsulated / opened) and analysed the spatial relative force vectors of the prodorsum lateral adjustor muscles (pla) which are responsible for retraction and adjustment of the prodorsum during encapsulation. We show that the functional morphology of these muscles strongly differs between the two species and that this can be explained by the structure of corresponding cuticular elements. Furthermore, the dynamics of pla, as measured by the extent of contraction during encapsulation, is more than two times higher in R. ardua than in O. banksi.     

Internal and external morphology of the deutonymph of Caloglyphus boharti (Arachnida: Acari)

A band of flexible cuticle encircles the deutonymph, separating the dorsal and ventral plates. The coxae are large, flat and fused with one another to form most of the ventor. Individual coxal margins are redefined as sternites, epimerites or simply apodemes according to which margins fuse with which others. A given area of cuticle may have patches of dark or light cuticle not corresponding to particular structures or cuticular contours; this is a source of confusion to taxonomists. Each leg has a dicondylic coxal-trochantal (adduction-abduction) and trochantal-femoral (promotion-remotion) joint with opposing muscles. The three more distal monocondylic joints (flexion-extension) have only flexor muscles; extension is by increased haemolymph pressure. The five apodemes of the sucker plate provide rigidity; the four suckers attach by a flexible cuticular ring to a solid flange or socket in the sucker plate. The sucker muscles attach to the center of each sucker. The flat, external face of the sucker plate apodemes may complement sucker action by adhesion. Coxal discs and sucker plate discs are identical, contain birefringent cuticular elements, and are considered modified setae. Functional mouthparts and a pharynx are lacking, but a cheliceral anlage is present. The esophagus, midgut and caecae, and malpighian tubules are lumenless and the cells small. The hindgut has a lumen, larger cells and opens externally via the anus. Whereas the digestive tract is regressed, the reproductive system is yet incompletely developed. In older deutonymphs anlagen of ducts, accessory glands and gonads are discernible. The nature of the haemocoel and peritoneum remains nuclear. The central nerve mass is conspicuously large for the size of the deutonymph. The supraesophageal ganglion gives rise to the cheliceral nerves; all other nerves arise from the subesophageal ganglion. Most major nerves were traced to the effector organs. The muscles are divided into leg, dorso-ventral (derived from coxal muscles), dorsal, sucker, and anogenital muscles. The trochantal adductor muscles originate on an endosternite, which is supported by muscles running to the dorsal hysterosoma. The dorso-ventral and propodosomal retractor muscles affect haemolymph pressure. The massive sucker retractor muscles are unique to this instar. Anogenital muscles are not well developed.     

Tinaminyssus juxtamelloi sp. n. (Acari: Dermanyssidae; Rhinonyssinae) from the nasal passages of the band-tailed pigeon, Columba fasciata, in New Mexico.

Tinaminyssus juxtamelloi sp. n. is described from the nasal passages of Columba fasciata in New Mexico. The new species is most similar to Tinaminyssus melloi (Castro) 1948 and T. turturi (Fain) 1962, but differs in (1) possessing only 5 pairs of ventral opisthosomal setae, (2) presence of 3 pairs of enlarged setae on the dorsal opisthosoma at the posterolateral margin of the podosomal plate (1 pair) and at the lateral margins of the opisthosomal plate (2 pairs), (3) elongate shape and larger size of the poststigmatic plates, and (4) chaetotaxy and solenidiotaxy of the legs, especially tarsus I with a cluster of 4 solenida and 1 club-shaped solenidion on the apex of the dorsum. The relationships of this with allied species of the genus Tinaminyssus from columbiform birds are briefly discussed.     

Morphology of the prosomal endoskeleton of Scorpiones (Arachnida) and a new hypothesis for the evolution of cuticular cephalic endoskeletons in arthropods

Skeletomuscular anatomy of the scorpion prosoma is examined in an attempt to explain the evolution of two endoskeletal features, a muscular diaphragm dividing the prosoma and opisthosoma and cuticular epistomal entapophyses with a uniquely complex arrangement of muscles, tendons and ligaments. Both structures appear to be derived from modifications of the mesodermal intersegmental endoskeleton that is primitive for all major arthropod groups. The scorpion diaphragm is a compound structure comprising axial muscles and pericardial ligaments of segments VI to VIII and extrinsic muscles of leg 4 brought into contact by longitudinal reduction of segment VII and integrated into a continuous subvertical sheet. This finding reconciles a long-standing conflict between one interpretation of opisthosomal segmentation based on scorpion embryology and another derived from comparative skeletomuscular anatomy. A new evolutionary-developmental mechanism is proposed to account for the complex morphology of the epistomal entapophyses. Each entapophysis receives 14 muscles and tendons that in other taxa would attach to the anterior connective endoskeleton in the same relative positions. This observation suggests that the embryological precursor to the connective endoskeleton can initiate and guide ectodermal invagination and thereby serve as a spatial template for the development of cuticular apodemes. This mesoderm-template model of ectodermal invagination is potentially applicable to all arthropods and may explain structural diversity and convergence in cephalic apodemes throughout the group. The model is used to interpret the cephalic endoskeletons of two non-chelicerate arthropods, Archaeognatha (Hexapoda) and Symphyla (Myriapoda), to demonstrate the generality of the model.     

A new genus and species of oribatid mites <Emphasis Type="Italic">Scarabacarus longisensillus</Emphasis> gen. et sp. n. (Acariformes,Liacaridae) from the Caucasus

A new genus and species, Scarabacarus longisensillus gen. et sp. n., of the family Liacaridae are described from the Caucasus (Azerbaijan and Abkhazia): The new genus Scarabacarus is characterized by the highly convex body, straight anterior margin of the notogaster, narrow fusiform sensilla, the lamellae situated on the lateral margins of the prodorsum, the absence of interlamellar and notogastral setae (besides one posterior pair), presence of four pairs of genital setae, and tridactylous leg tarsi.     

Out-of-the tropics or trans-tropical dispersal? The origins of the disjunct distribution of the gooseneck barnacle Pollicipes elegans

Myogenesis is currently investigated in a number of invertebrate taxa using combined techniques, including fluorescence labeling, confocal microscopy, and 3D imaging, in order to understand anatomical and functional issues and to contribute to evolutionary questions. Although developmental studies on the gross morphology of bivalves have been extensively pursued, organogenesis including muscle development has been scarcely investigated so far. The present study describes in detail myogenesis in the scallop Nodipecten nodosus (Linnaeus, 1758) during larval and postmetamorphic stages by means of light, electron, and confocal microscopy. The veliger muscle system consists of an anterior adductor muscle, as well as four branched pairs of striated velum retractors and two pairs of striated ventral larval retractors. The pediveliger stage exhibits a considerably elaborated musculature comprising the velum retractors, the future adult foot retractor, mantle (pallial) muscles, and the anterior and posterior adductors, both composed of smooth and striated portions. During metamorphosis, all larval retractors together with the anterior adductor degenerate, resulting in the adult monomyarian condition, whereby the posterior adductor retains both myofiber types. Three muscle groups, i.e., the posterior adductor, foot retractor, and pallial muscles, have their origin prior to metamorphosis and are subsequently remodeled. Our data suggest a dimyarian condition (i.e., the presence of an anterior and a posterior adductor in the adult) as the basal condition for pectinids. Comparative analysis of myogenesis across Bivalvia strongly argues for ontogenetic and evolutionary independence of larval retractors from the adult musculature, as well as a complex set of larval retractor muscles in the last common bivalve ancestor.     

Two new species of Pergalumna (Acari,Oribatida, Galumnidae) from Costa Rica,including a key to all species of the genus from the Neotropical region

Two new species of oribatid mites of the genus Pergalumna (Oribatida, Galumnidae), P. elongatiporosa sp. n. and P. striatiprodorsum sp. n., are described from leaf litter of a secondary forest in Costa Rica. Pergalumna elongatiporosa sp. n. is most similar morphologically to P. horvathorum P. Balogh, 1997 and P. sura P. Balogh, 1997, however, it differs from both by the body size, body surface ornamentation and morphology of notogastral porose areas A1 and A3. Pergalumna striatiprodorsum sp. n. is most similar morphologically to P. hawaiiensis hawaiiensis (Jacot, 1934) and P. strigulata Mahunka, 1978, however, it differs from P. hawaiiensis by the length of interlamellar setae and surface ornamentation of the prodorsum; from P. strigulata by the surface of ornamentation of the notogaster, length of interlamellar setae and morphology of bothridial setae. An identification key to known species of Pergalumna from the Neotropical region is given.     

Anatomy of the extrinsic gut musculature of Gammarus minus (Crustacea: Amphipoda)

Inserting on the buccal and esophageal foregut of Gammarus minus are numerous pairs of serially arranged dorsal dilator muscles, a single pair of lateral muscles, and two pairs of posterior muscles. Muscles of the cardiac stomach include three dorsal sets, a single pair associated with the pterocardiac ossicles, and two pairs inserting on the ventral aspect. A single pair of muscles inserts on the lateral aspect of the pyloric stomach. The extrinsic muscles of the foregut originate from exoskeletal apodemes of the cephalothoracic cuticle, sockets of the mandible, and a maxillary bridge that lies just ventral to the cardiac stomach. The extrinsic musculature of the hindgut is restricted to the rectal region and consists of paired dorsal and ventral series in an X-configuration. A single unpaired muscle inserts on the ventral midline. Extrinsic muscles of the hindgut originate from the integument of the last pleonic segment. The general arrangement of extrinsic gut muscles in G. minus is similar but not identical to that of other amphipods studied. However, the pattern is quite different from that of other malacostracans.     

Centers of mass and weight distribution in spiders of the family uloboridae

In the Uloboridae, web reduction is accompanied by changes in opisthosomal shape, leg length, and web-monitoring tactics. These morphological changes make reduced-web spiders more cryptic and alter their leg leverage and centers of mass. When compared with the orb-weaver Uloborus glomosus, the irregular, reduced-web spider, Miagrammopes animotus, invests more mass in its prosoma and first legs. However, the latter species' elongate opisthosoma posteriorly shifts this region's center of mass, causing the relative position of its composite center of mass and the distribution of weight between its first and fourth legs to be similar to that of the orb-weaver. Like these species, the opisthosomal center of mass of the triangle-weaver, Hyptiotes cavatus, lies near its midpoint. However, the shorter first legs and rounder, heavier opisthosoma of Hyptiotes posteriorly shift its composite center of mass and distribute more of its weight onto its fourth legs. Consequently, the morphology of M. animotus can be adequately explained by its adaptiveness for web manipulation, balance, and weight distribution and the crypsis that these features confer as an ancillary advantage. In contrast, anatomical changes in H. cavatus are better explained as adaptations for web manipulation and crypsis.     

Oribatid mites (Acari,Oribatida) from the Oumé region (Côte d’Ivoire): list of taxa,new findings,description of a new species

The present study is based on oribatid mite material (Acari, Oribatida) collected from the Oumé region (Côte d’Ivoire, West Africa) in 2007. A list of identified taxa, including 67 species from 50 genera and 31 families, is presented; all species, genera and families are registered in this country for the first time; Kalloia simpliseta, Scheloribates latoincisus and Pergalumna paraelongata are recorded in the Ethiopian region for the first time. One new species of the genus Arcoppia (Oppiidae) is described; A. goulikaoensis Ermilov sp. n. differs from A. robusta Mahunka, 1988 by the well-developed bothridial heads (versus not developed), barbed branches on the bothridial setae (versus smooth) and smooth notogaster surface (versus lineolate).     

THE ADDUCTOR AND RETRACTOR MUSCLES OF THE VELIGER OF PECTEN MAXIMUS (L.) (BIVALVIA)

In Pecten maximus (L.), retractor and adductor muscles becomefunctional in the early veliger larva. The twelve-day-old veligerhas four pairs of velar retractors, three pairs of retractorsattached to the posterior body wall and an anterior adductor.The pediveliger has in addition, pedal retractor muscles anda posterior adductor. The retractors consist of striated muscle:the adductors have both smooth and striated portions. The retractorsattach near the hinge, branch to a greater or lesser extent,then attach to specific areas of the velum, posterior body walland foot. Some features of the branching and of the dispositionof points of attachment form a pattern which exhibits mirrorsymmetry about the plane between the two shell valves. Thispattern is characteristic of the species. It is deduced thatretraction and protraction of the velum result from co-ordinatedsequences of muscle contractions. ^*Present address: Forest Products Research Centre, P.O. Box1358, Boroko, Papua New Guinea. (Received 15 June 1984;     

Motor output to the protractor and retractor coxae muscles in stick insects walking on a treadwheel

ABSTRACT. The motor output to the protractor and retractor mucles moving the coxa of the middle leg of Carausius morosus was recorded from the thoracic nerves during walking on a treadwheel. The leg movements on the wheel were generally similar to those found in free-walking animals, but tripod coordination was relatively independent of period, and the coordination of the adult animal on the wheel was most closely related to that found in free-walking first instars. The activity of a common inhibitor and four excitatory axons of the retractor and an excitatory axon of the protractor were followed for 850 steps (in six animals) to give a summary of the behaviour of the different units. The motor activity is less stereotyped than that previously reported for insects. There was strong reciprocity between the antagonists, but this was not directly correlated with the forward and backward movements of the legs. The first part of the stance phase of the leg was accompanied by a strong burst in the protractor nerve and relatively little retractor activity. This was followed by the main retractor burst which occupied the last 60% of the stance phase. The results are compared with motor output records of the locust and with earlier force-plate measurements on the stick insect. It must be concluded that the mesothoracic leg initially resists forward movement of the body by the other legs during a typical walking step.     

Finite element modeling of the left atrium to facilitate the design of an endoscopic atrial retractor

With the worldwide prevalence of cardiovascular diseases, much attention has been focused on simulating the characteristics of the human heart to better understand and treat cardiac disorders. The purpose of this study is to build a finite element model of the left atrium (LA) that incorporates detailed anatomical features and realistic material characteristics to investigate the interaction of heart tissue and surgical instruments. This model is used to facilitate the design of an endoscopically deployable atrial retractor for use in minimally invasive, robotically assisted mitral valve repair. Magnetic resonance imaging (MRI) scans of a pressurized explanted porcine heart were taken to provide a 3D solid model of the heart geometry, while uniaxial tensile tests of porcine left atrial tissue were conducted to obtain realistic material properties for noncontractile cardiac tissue. A finite element model of the LA was constructed using ANSYS Release 9.0 software and the MRI data. The Mooney-Rivlin hyperelastic material model was chosen to characterize the passive left atrial tissue; material constants were derived from tensile test data. Finite element analysis (FEA) models of a CardioVations Port Access retractor and a prototype endoscopic retractor were constructed to simulate interaction between each instrument and the LA. These contact simulations were used to compare the quality of retraction between the two instruments and to optimize the design of the prototype retractor. Model accuracy was verified by comparing simulated cardiac wall deflections to those measured by MRI. FEA simulations revealed that peak forces of approximately 2.85 N and 2.46 N were required to retract the LA using the Port Access and prototype retractors, respectively. These forces varied nonlinearly with retractor blade displacement. Dilation of the atrial walls and rigid body motion of the chamber were approximately the same for both retractors. Finite element analysis is shown to be an effective tool for analyzing instrument/tissue interactions and for designing surgical instruments. The benefits of this approach to medical device design are significant when compared to the alternatives: constructing prototypes and evaluating them via animal or clinical trials.     

Segment-specific retention of a larval neuromuscular system and its role in a new, rhythmic, pupal motor pattern in Manduca sexta

At pupation in Manduca sexta, accessory planta retractor muscles and their motoneurons degenerate in segment-specific patterns. Accessory planta retractor muscles in abdominal segments 2 and 3 survive in reduced form through the pupal stage and degenerate after adult emergence. Electromyographic and electrophysiological recordings show that these accessory planta retractor muscles participate in a new, rhythmic `pupal motor pattern' in which all four muscles contract synchronously at ∼4 s intervals for extended bouts. Accessory planta retractor muscle contractions are driven by synaptic activation of accessory planta retractor motoneurons and are often accompanied by rhythmic activity in intersegmental muscles and spiracular closer muscles. The pupal motor pattern is influenced by descending neural input although isolated abdominal ganglia can produce a pupal motor pattern-like rhythm. The robust pupal motor pattern first seen after pupal ecdysis weakens during the second half of pupal life. Anemometric recordings indicate that the intersegmental muscle and spiracular closer muscle component of the pupal motor pattern produces ventilation. Accessory planta retractor muscle contractions lift the flexible abdominal floor, to which the developing wings and legs adhere tightly. We hypothesize that, by a bellows-like action, the accessory planta retractor muscle contractions circulate hemolymph in the appendages. Morphometric analysis shows that dendritic regression is similar in accessory planta retractor motoneurons with different pupal fates, and that accessory planta retractor motoneurons begin to participate in the pupal motor pattern while their dendrites are regressed. Accepted: 29 March 1998     

The anatomy of the adult uropodid Fuscouropoda agitans (Arachnida; Acari), with comparative observations on other Acari

A thin, compressible, lateral suture and ventral plate overlap permit limited movement of the thick and rigid dorsal and ventral plates of Fuscouropoda agitans. Seven pairs of large dermal glands debouch onto the surface. Trochanteral rotation permits defensive leg adpresion and an insectan type of ambulation. The complex hypopharynx-pedipalpal-coxae has a buccal and cheliceral cavity separated by an atriculated epipharynx. The pharynx is Y-shaped in cross section. Extensive paired salivary glands lie above the very long and dexterous 3-segmented chelicerae, and a large pair of coxal glands debouch on coxae 1. From four blunt-ended tracheae, bundles of unbranching tracheoles extend in specific tracts to all organs. The ventriculus is small with three pairs of large caeca; a tightly packed single layer of digestive cells individually enlarged to absorb-phagocytize and digest the food. A typical mesostigmatid excretory tube is present. A typical acarine synganglion is present; mixed nerves have a basal swelling. A postulated neurosecretory organ arises from the pedipalpal nerve. The oocytes enlarge within funicular stalks from the walls of the small median ovary. A large spermatophore is stored in the seminal vesicle; fertilization occurs during oviposition. A tension hinge partially opens both male and female genital plates; closure effected by muscles acting on very long genital plate apodemes. Within sequentially produced spermatogonial cysts of the testes, meiosis is completely synchronous. A large, multilobed male accessory gland produces a large volume of seminal fluid; a mixture of at least four secretions. The origins and msertions of the body wall, genital organ, digestive tract, mouthpart and leg muscles are listed and illustrated. A comparison of anactinotrichid and actinotrichid mites indicates fundamental and consistent morphological differences in aspects of the cuticle, leg articulations, digestive system, excretory system, reproductive system and coxal glands.     

Avoidance reflexes mediated by contact chemoreceptors on the legs of locusts

Taste receptors, or basiconic sensilla, are distributed over the legs of the locust and respond to direct contact with chemical stimulants. The same chemosensory neurones that responded to contact with salt solutions also responded to particular acidic odours. Odours of food and other chemicals had no effect on the chemosensory neurones. In locusts free to move, an acid odour presented to the tarsus of a hind leg evoked a rapid avoidance movement in which the tarsus was levated, the tibia flexed and the femur levated. Intracellular recordings from motor neurones that innervate muscles of the hind leg showed that when an acid odour was directed towards basiconic sensilla on the leg there was a reciprocal activation of antagonistic motor pools that move the leg segments about each joint. Thus an extensor tibiae motor neurone was inhibited while a flexor tibiae motor neurone was excited, and the tarsal depressor and retractor unguis motor neurones were inhibited while the tarsal levator motor neurone was excited. This method of odour stimulation of taste receptors generates less adaptation than direct contact with chemicals, and therefore represents an ideal method for stimulating taste receptors for further studies on the central pathways processing taste signals. Accepted: 2 June 1998     

Somatic musculature of rotifers <Emphasis Type="Italic">Asplanchna girodi</Emphasis> Guerne, 1888 and <Emphasis Type="Italic">Trichotria pocillum</Emphasis> (Müller, 1776) (Rotifera,Pseudotrrocha, Ploima): Comparative aspect

Comparative study of somatic musculature in illoricate rotifer Asplanchina girodi Guerne, 1888 and loricate Trichotria pocillum (Müller, 1776) has been carried out by the method of phalloidin fluorescence and confocal laser scanning microscopy. Similar layering of muscles is revealed, while significant differences are observed in other aspects. Postcoronal transverse muscle of A. girodi and the dorsal portion of the anterior circular muscle of T. pocillum serve as attachment sites for the refractor muscles. All retractors are formed by smooth muscles or striated muscles, except the lateral retractors of A. girodi, which are formed by the most powerful oblique muscles. In A. girodi there are three pairs of retractors, ten longitudinal muscles, and five circular muscles, with a thick muscular plexus connecting them. In T. pocillum there are four pairs of retractors, five transverse muscles, strong foot retractors, and an arched structure of the head region (new for rotifers). Eight pairs of dorsoventral muscles, as identified in T. pocillum, are completely absent in A. girodi.