Ultrastructure of the sensory palps ofTetranchyroderma papii (Gastrotricha,Macrodasyida)

Summary The sensory palps of the macrodasyoid gastrotrichTetranchyroderma papii contain processes from two types of cell: 22–23 bipolar primary sensory cells and two to three support cells. In the proximal region of the palp each sensory cell contains a short ciliary segment with a basal body and from this ciliary segment a longer distal segment lacking axonemal microtubules extends through the major part of the length of the palp. Each support cell process bears microvilli and contains a conspicuous bundle of microtubules running the entire length of the process. The cell bodies of both cell types are situated in the epidermis of the head region. The palps are interpreted as having a chemosensory function. They are considered to be homologous to the posterior cephalic sensory organ ofTurbanella cornuta, but not the head tentacles ofChordodasys antennatus or nematode amphids.     

Macrodasyida (Gastrotricha): a cladistic analysis of morphology

Abstract. A cladistic analysis based on 33 morphological characters was performed for the 31 genera currently assigned to the order Macrodasyida (Gastrotricha). Outgroup analysis indicated that the order is monophyletic and that it is defined by the structure of the pharynx and the complex distribution of duo-gland adhesive organs. Of the 6 currently recognized families in Macrodasyida, our analysis confirmed that 4 families are monophyletic: Dactylopodolidae, Macrodasyidae, Thaumastodermatidae and Turbanellidae. Dactylopodolidae was further confirmed as the most basal family within the order based on the retention of several plesiomorphies. The other three families have well-defined autapomorphies but will require further investigation to increase inter- and intrafamilial phylogenetic resolution. Planodasyidae appeared to be a paraphyletic taxon with no obvious autapomorphies; genera clustered among members of a polyphyletic family, Lepidodasyidae. We recommend that future research on macrodasyidan phylogeny focus on issues of comparative morphology and ultrastructure in lesser-known taxa such as the Dactylopodolidae, and on the taxa Lepidodasyidae and Planodasyidae.     

Functional morphology of the muscles in Philodina sp. (Rotifera: Bdelloidea)

Whole-mounts of Philodina sp., a bdelloid rotifer, were stained with fluorescent-labeled phalloidin to visualize the musculature. Several different muscle types were identified including incomplete circular bands, coronal retractors and foot retractors. Based on the position of the larger muscle bands in the body wall, their function during creeping locomotion and tun formation was inferred. Bdelloid creeping begins with the contraction of incomplete circular muscle bands against the hydrostatic pseudocoel, resulting in an anterior elongation of the body. One or more sets of ventral longitudinal muscles then contract bringing the rostrum into contact with the substrate, where it presumably attaches via adhesive glands. Different sets of ventral longitudinal muscles, foot and trunk retractors, function to pull the body forward. These same longitudinal muscle sets are also used in `tun' formation, in which the head and foot are withdrawn into the body. Three sets of longitudinal muscles supply the head region (anterior head segments) and function in withdrawal of the corona and rostrum. Two additional pairs of longitudinal muscles function to retract the anterior trunk segments immediately behind the head, and approximately five sets of longitudinal retractors are involved in the withdrawal of the foot and posterior toes. To achieve a greater understanding of rotifer behavior, it is important to elucidate the structural complexity of body wall muscles in rotifers. The utility of fluorescently-labeled phalloidin for the visualization of these muscles is discussed and placed in the context of rotifer functional morphology.     

Functional morphology of the endomysium in series fibered muscles.

Many skeletal muscles, including the feline biceps femoris, are composed of short, tapered myofibers arranged in an overlapping longitudinal series. The endomysium of such muscles transfers tension between overlapping myofibers, and is thus an elastic element in series with them. The endomysium of the cat biceps femoris contains curvilinear collagen fibrils in an approximately isotropic (random) array. The collagen fibrils undergo only a modest reorientation as the myofibers shorten or lengthen within the physiological range. A geometrical model predicts no change in the thickness of the endomysium on changing muscle fiber length and quantifies the expected collagen fibril reorientation in the endomysium as a function of muscle extension. It is also demonstrated that a high proportion of the collagen fibrils will be curvilinear at all sarcomere lengths. The organization of endomysial collagen is appropriate for the transfer of loads between myofibers by means of shear.     

Sinneseinrichtungen beiTurbanella cornuta Remane (Gastrotricha)

Zusammenfassung Es wurde die Feinstruktur von drei Sinneseinrichtungen untersucht, die am Vorderende vonTurbanella cornuta (Gastrotricha) liegen.DieSinneshaare sind primÄre und bipolare Sinneszellen mit einer apikalen Zilie, die von Stereozilien umgeben wird. Dashintere Kopfsinnesorgan enthÄlt 12–14 primÄre, bipolare Sinneszellen, die mit einigen Becherzellen gemeinsam ein extrazellulÄres Organlumen umstellen. In das Lumen münden die an ihren Enden aufgezweigten Dendriten ein. Bei demvorderen Kopfsinnesorgan münden zwei Dendriten in ein Organlumen ein und spalten sich in viele regelmÄ\ige Mikrovilli auf, die jeweils einen Innentubulus enthalten. Die Dendriten der beiden letzteren Sinnesorgane besitzen eine Züienregion.Es ist anzunehmen, da\ die drei Arten von Sinneseinrichtungen verschiedene Funktionen haben. Es wird diskutiert, ob den Sinneshaaren möglicherweise eine mechanorezeptive Funktion, den hinteren Kopfsinnesorganen eine chemorezeptive Funktion und den vorderen Kopfsinnesorganen eine Lichtsinnesfunktion zukommt.

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Sensory devices inTurbanella cornuta remane (Gastrotricha)

Summary At the head ofTurbanella cornuta (Gastrotricha) three types of sensory devices are recognized.Thesensory hairs are primary and bipolar cells with an apical cilium that is surrounded by sterocilia. Theposterior sense organ of the head contains 12–14 primary and bipolar sensory cells. These cells and some secretory cells form an extracellular lumen, where the dendrits of sensory cells penetrate with several swallen terminals. Concerning theanterior sense organ of the head two dendrits penetrate into a common lumen and branch out into a lot of regular microvilli, each of which contains one single microtubule. The dendrits of the anterior and posterior sense organs are separated into an inner and an outer segment by a ciliar region.Probably the described sensory devices are coordinated to different functions. It is discussed wheather the sensory hairs have a mechanical function, the posterior sense organs of the head have a chemical function and the anterior sense organs of the head are sensitive to light.

     

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.     

Functional morphology of the tongue muscles of some Indian insect-eating birds

In the complex feeding apparatus of birds, the tongue muscles also play an important role like the jaw muscles. Among the passerine birds, the tongue muscles exhibit greater structural uniformity than the jaw muscles. The elaborate system of extrinsic tongue musculature brings about all necessary movements of the tongue. The intrinsic tongue musculature in all the birds studied is extremely weak and reduced. The principal tongue muscles are better developed in Turdoides and Copsychus than in the other birds. However, in Orthotomus, Anthus, Dicrurus, and Merops, some of the tongue muscles are quite well developed, perhaps compensating for the deficiencies of the other muscles. The origin of M. branchiomandibularis posterior from the outer mandibular ramus in Orthotomus, Dicrurus, and Merops is remarkable, but its occurrence may not be unusual among the passerine birds. Some variations are also observed in the origin and insertion of M. genioglossus in Turdoides, Copsychus, and Anthus. The correlations between the structures and functions of the tongue muscles are not always possible without considering the synergistic actions of the other muscles.     

Global diversity of gastrotrichs (Gastrotricha) in fresh waters

The global diversity of inland water Gastrotricha is poorly known, and information is extremely heterogeneous. Gastrotricha have been studied most widely in Europe and America, whereas data from the other continents are scattered or not even available. This scanty information is related to several reasons, first of which is the technical difficulty in collecting and studying microscopic and soft-bodied species. In addition, the research has been limited mostly to the epibenthos and periphyton in lentic waters, and the gastrotrich taxonomy is still under discussion mainly because of the great intraspecific variability. Three of the five freshwater families are widespread or cosmopolitan, and most genera have been reported from at least two continents. There is strong evidence of a high diversity in genera and species in tropical areas. Nearly a half of the freshwater species are known from only one country or even only from one site, but the insufficient faunistic knowledge does not allow defining them as endemic. The phylogenetic relationships and possible evolutionary trends of inland water species of Gastrotricha are outlined. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

The Behavior of Heterolepidoderma sp. (Gastrotricha)

The behavior of Heterolepidoderma sp. was studied with the same approach as those already used for many species of ciliates. The ethogram we drew comprehends both helicoidal swimming (n = 20, r = 52.5 +/-12.2 mum, pitch = 512 +/- 101 mum, v--> = 215 +/- 43 mum/sec), periodically interrupted by irregular patterns changing the direction of the swimming of random angles and creeping on the substrate. The latter behavioral state, very common for the species we studied, occurs along tracks formed by successive elements (circular, C, vs linear segments, S) joined to each other by two kinds of reactions, which change their trajectory. The surprising similarities and the unexpected differences between the behavior of this gastrotrich and those of the ciliates already studied from this point of view are discussed, on the basis of the dimensional ranges and ecological niches shared by these two, definitely unrelated groups of organisms.     

Zur fortpflanzung und entwicklung der macrodasyoidea (Gastrotricha)

Comparative investigations of the reproduction and development of the Macrodasyoidea are made on the species Turbanella cornuta, Macrodasys caudatus, Cephalodasys muximus, Dactylopodalia baltica and some others.The Macrodasyoidea have a direct development. The divisions of the best studied species, Turbanella cornuta, is total, equal and bilateral. The cell-lineage produces a 30-cell stage in which gastrulation by invagination of two entoderm cells followed by mesodermal cells occurs. Two compact mesodermal strands segregate the germ cells and give rise to the muscular system and the y-organ. Agreements in the embryology of the gastrotrichs and the nematodes support the postulation of a close relationship between them.     

Ultrastructure of the protonephridial system in Neodasys chaetonotoideus (Gastrotricha: Chaetonotida) and in the ground pattern of Gastrotricha

The taxon Neodasys has a basal position within Gastrotricha. This makes it very interesting for phylogenetic considerations in this group. To complete the reconstruction of the nephridial system in the stem species of Gastrotricha started earlier, we have studied the whole protonephridial system of Neodasys chaetonotoideus by means of complete sets of ultrathin sections and TEM. In many characters, protonephridia of N. chaetonotoideus resemble those of macrodasyidan gastrotrich species. For example, each of the six protonephridia, arranged in three pairs, consists of three distinct cells that constitute the continuous protonephridial lumen. Especially, the terminal cell of the protonephridia of N. chaetonotoideus shows a striking pattern: The perforation of the filter region is a meandering cleft that is continuous with the seam of the enfolded lumen of that cell. With the results presented here and that of former TEM studies, we give a comprehensive idea of the excretory organs in the ground pattern of Gastrotricha. Moreover, we can elaborate on the hypothesized protonephridial system in the stem species of Bilateria. We suggest that a meandering filtration cleft is a feature of the ground pattern of the Bilateria.     

暗纹东方鲀应激胀气行为功能形态学观察

该文以四齿鲀科(Tetraodontidae)的暗纹东方鲀(Takifugu obscurus)为对象,采用形态学解剖、X光透视和骨骼神经染色等方法,对其胀气行为的功能形态学进行研究。其结果发现,暗纹东方鲀腹部受到刺激后,口腔小幅高频将水或空气吞咽进入由食道腹壁特化成的气囊里,气囊与消化道的前后结合处由括约肌控制,腹壁肌呈束状,与此同时,高弹性的皮肤、脊柱和神经都会发生相应的位移变化,以保证胀气行为的快速完成。通过对暗纹东方鲀胀气行为及其吸、排水机制的深入了解,为进一步研究胀气行为的神经机理奠定基础,也将会丰富动物警戒逃避行为的理论。     

Functional morphology of locomotion in Derocheilocaris typica (Crustacea,Mystacocarida)

Summary The crustacean class Mystacocarida is restricted to the interstitial marine sand environment. A cinemicrographic analysis of the functional morphology of locomotion in the mystacocarid D. typica was undertaken to demonstrate how this species progresses through the interstitial spaces. Locomotion is completely dependent on the presence of dorsal and ventral substrates. The biramous second antennae and mandibles are the force-generating appendages. During a locomotory cycle, the exopods of the second antennae and mandibles are directed dorsolaterally against a dorsal substrate. This creates a downward force enabling the endopods to gain purchase on the ventral substrate. The second antennae and mandibles undergo coordinated cyclic movements. Each cycle results in two power and two recovery strokes. The animals undergo approximately 4 complete cycles per second. The calculated maximum rate of locomotion is 420 m/s. The measured rate under test conditions is 250 m/s. A turning-escape reaction in response to air bubbles and other factors results in a 180° turn in a confined space within 1.5 s. These data are discussed in relation to the morphological conservatism of mystacocarids, their presumed neotenic origin and their observed migration over a tidal cycle. It is proposed that all crawling interstitial animals will have developed specific mechanisms to increase frictional forces between their locomotory appendages and the surrounding substrate.This investigation was supported in part by a National Science Foundation grant # DEB-7823395 to E. Ruppert. Contribution # 442 of the Belle W. Baruch Institute for Marine and Coastal Research     

A new non-naked species of Ptychostomella (Gastrotricha) from Brazil

A new species of marine Gastrotricha from Brazil is described and discussed. Ptychostomella lamelliphorasp. n. is one of the several new taxa that were found during an extensive survey of the gastrotrich fauna carried out in 2002 and 2003 along the coastline of the State of São Paulo. The new species is unique in that it possesses cuticular ornamentations in the form of plate-like structures (scales) along the lateral borders of the body and two massive clusters of densely packed adhesive tubes on the ventral surface, near the ano-genital opening. Both these features appear to be adaptations to challenge the high energy waters that characterize the species’ microhabitat: the coarse sublittoral sand in the channel between the mainland and the largest island in the State, Ihlabela. Additionally, a key to the described Ptychostomella species of the world is provided.     

Functional morphology of the Conus proboscis (Mollusca: Gastropoda)

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

Functional forewing morphology and stridulation in crickets (Orthoptera, Grylloidea)

Forewing morphology and infrastructure are analysed in three cricket species ( Gryllus campestris, Oecanthus pellucens and Lerneca fuscipennis ) and checked in 20 other genera. A strong dorsoventral asymmetry is demonstrated for the first time. The upper side of the tegmina is covered with hexagonal, more or less high crests forming reliefs. On the lower side, annulate, flat and thick veins exist. The distribution of the hexagons and that of the different vein types is uneven on the forewing surfaces. Their significance in forewing functional morphology is discussed in relation to stridulation and to current knowledge on cricket sound production mechanisms. Their extent and distribution, together with the number and strength of the veins and the surface of wing cells, could account for the vibrational characteristics of the cricket forewing and explain the diverse results obtained by several authors on Gryllus and Oecanthus .     

Functional morphology of bite mechanics in the great barracuda (Sphyraena barracuda)

The great barracuda, Sphyraena barracuda, is a voracious marine predator that captures fish with a swift ram feeding strike. While aspects of its ram feeding kinematics have been examined, an unexamined aspect of their feeding strategy is the bite mechanism used to process prey. Barracuda can attack fish larger than the gape of their jaws, and in order to swallow large prey, can sever their prey into pieces with powerful jaws replete with sharp cutting teeth. Our study examines the functional morphology and biomechanics of 'ram-biting' behavior in great barracuda where the posterior portions of the oral jaws are used to slice through prey. Using fresh fish and preserved museum specimens, we examined the jaw mechanism of an ontogenetic series of barracuda ranging from 20 g to 8.2 kg. Jaw functional morphology was described from dissections of fresh specimens and bite mechanics were determined from jaw morphometrics using the software MandibLever (v3.2). High-speed video of barracuda biting (1500 framess(-1)) revealed that prey are impacted at the corner of the mouth during capture in an orthogonal position where rapid repeated bites and short lateral headshakes result in cutting the prey in two. Predicted dynamic force output of the lower jaw nearly doubles from the tip to the corner of the mouth reaching as high as 58 N in large individuals. A robust palatine bone embedded with large dagger-like teeth opposes the mandible at the rear of the jaws providing for a scissor-like bite capable of shearing through the flesh and bone of its prey.     

Functional morphology of dewlap extension in the lizard Anolis equestris (Iguanidae)

The dewlap is an extendible flap of skin ordinarily folded under the throat. Lizards, particularly those in the genus Anolis, extend their dewlaps during interactions with conspecifics, other lizards, and potential predators. Dewlap extension is effected by movements of elements of the hyoid apparatus. This paper describes the anatomy of the hyoid and associated musculature in Anolis equestris, a large arboreal lizard with a prominent dewlap. A mechanism for dewlap extension is proposed based on results of morphological and experimental techniques. Specializations of the hyoid skeleton for dewlap extension include elongated second ceratobranchials and highly movable joints between the ceratohyals and the hypohyals and between the first ceratobranchials and the body of the hyoid. A well developed M. ceratohyoideus extends between the ceratohyals and the first ceratobranchials of the hyoid apparatus. During dewlap extension, the hyoid apparatus acts as a first order lever. Contraction of M. ceratohyoideus pulls the ceratohyals posteriorly causing the hypohyals and the body of the hyoid to rotate dorsally around the first ceratobranchial/body joints. This movement results in the second ceratobranchials swinging forward and down, unfolding the dewlap. The relative immobility of the first ceratobranchials provides stability to the hyoid apparatus during dewlap extension. A comparison is made of dewlap extension and other hyoid displays.