Muscular waves contribute to gliding rate in the freshwater gastropod Lymnaea stagnalis

This study revises the mechanisms of ciliary locomotion and demonstrates muscular contribution to locomotion rate in Lymnaea stagnalis. L. stagnalis sticks to the substratum by the foot sole and moves smoothly with no visible contractions of the foot. A ciliated epithelium covering the sole is underlain by smooth muscle cells containing giant mitochondria. It is shown here that slow (basal) locomotor activity (measured as the flow rate of physiological saline over isolated sole) appears spontaneously or is induced by 10⁻⁸–10⁻⁷ M 5-HT. 5-HT (10⁻⁷–10⁻⁴ M) facilitates locomotor activity dose-dependently, and KCN (an inhibitor of mitochondrial respiration) decreases these effects to the basal level. 5-HT and KCN have no effect on the frequency of ciliary beat (stroboscopic measurements), and blockers of anaerobic glycolysis inhibit ciliary motility. Under anaerobic conditions locomotion of a snail is slow and insensitive to 5-HT in contrast to that in aerobic environments. It is concluded that glycolysis supplies energy to ciliated cells and respiration to sole muscle cells; 5-HT stimulates ciliary beating in an all-or-none fashion and muscular waves in a dose-dependent manner; cilia provide slow (basal) gliding, and locomotory rate up to 80% above the basal level is determined by muscular waves.     

Burrowing,Locomotion and Other Movements of the Echiuran Ochetostoma caudex

Burrowing, iocomotory and other movements of the echiuran Ochetostoma caudex have been examined and discussed. A continuous body cavity enables the worm to undergo peristaltic waves to pump water through the burrow without causing locomotion. The animal is capable of both forward and backward locomotion in its burrow. During forward locomotion, retrograde peristaltic waves are utilized which advance the animal in a step-wise fashion. Pressure changes within the coelom during burrowing, locomotion and during irrigation movements have been measured with the use of electronic recording techniques and the results interpreted in relation to direct visual observation. The structural and functional specializations for burrowing are discussed and compared with the activities of Priapulus caudatus, Sipunculus nudus and Bonellia viridis.     

Adaptive design of locomotion and foot form in prosobranch gastropods

A comparison of the locomotor types, speed, tenacity, and foot form of nearly 300 species in 52 families of marine prosobranchs has revealed that foot size and shape and even subtle variations of locomotion affect the speed and strength of adhesion to the substratum.Gastropods inhabiting soft substrata move primarily by pedal cilia or by discontinuous locomotion in which shell and foot move alternately. Both types of movement are accompanied by low tenacity. A specialized type of discontinuous locomotion, namely, leaping, surpasses all other methods of movement in speed. Species with ciliary locomotion have a very large foot while those with discontinuous movement have an exceedingly small foot relative to shell size.The majority of prosobranchs inhabit hard substrata, move by continuous pedal muscular gliding, and have moderately high tenacity during movement. Arhythmic pedal locomotion yields lower maximum speeds and tenacities than do rhythmic pedal waves. Foot size and shape relative to shell length in species with arhythmic locomotion vary from very short and broad to long and narrow. Studies of transects at several temperate and tropical marine littoral stations showed that these species are confined to low littoral or sublittoral habitats that are sheltered from heavy wave action. High speed and tenacity are simultaneously attained only by species with rhythmic pedal waves.Speed and tenacity do not represent competing selective pressures on the size and shape of the foot. Speed increases among species as the foot approaches or exceeds shell length and is highest if the foot is also broad; the greatest tenacities are attained by species with a long, broad foot whose dimensions do not exceed that of the shell. The optimal shape for both high tenacity and speed is a broad foot somewhat shorter than the shell; neither speed nor tenacity are much compromised by this form. In general, only species with rhythmic pedal waves whose foot size and shape approximate the optimal form for high tenacity and speed are found in habitats exposed to much wave action. Long rhythmic waves, moving a large proportion of foot area at once, are in theory energetically more economical than small, very rapid waves resulting in the same overall speed, but experiments showed that tenacity is significantly reduced in gastropods which increase speed by enlarging the waves. The optimal wave pattern of a species should be a balance between the demand for speed with the least expenditure of energy, favored by a pattern of many large waves at once, and the demand for tenacity, favored by a pattern of few and small waves.Retrograde ditaxic waves of elongation are the most common pattern encountered among prosobranchs, and are associated with a large range of foot sizes and shapes. Such waves are at least one third as long as the foot, while direct waves and other waves of compression are frequently much smaller. The range of foot forms of species with waves of compression is restricted, tending to be optimal for high tenacity or to be long and narrow. Waves of compression appear to be a specialization with the potential for maintaining high tenacity even at high speeds since the waves can be very small, and for giving superior speed since they can travel very rapidly.     

Region-specific microtubule transport in motile cells

Photoactivation and photobleaching of fluorescence were used to determine the mechanism by which microtubules (MTs) are remodeled in PtK2 cells during fibroblast-like motility in response to hepatocyte growth factor (HGF). The data show that MTs are transported during cell motility in an actomyosin-dependent manner, and that the direction of transport depends on the dominant force in the region examined. MTs in the leading lamella move rearward relative to the substrate, as has been reported in newt cells (Waterman-Storer, C.M., and E.D. Salmon. 1997. J. Cell Biol. 139:417-434), whereas MTs in the cell body and in the retraction tail move forward, in the direction of cell locomotion. In the transition zone between the peripheral lamella and the cell body, a subset of MTs remains stationary with respect to the substrate, whereas neighboring MTs are transported either forward, with the cell body, or rearward, with actomyosin retrograde flow. In addition to transport, the photoactivated region frequently broadens, indicating that individual marked MTs are moved either at different rates or in different directions. Mark broadening is also observed in nonmotile cells, indicating that this aspect of transport is independent of cell locomotion. Quantitative measurements of the dissipation of photoactivated fluorescence show that, compared with MTs in control nonmotile cells, MT turnover is increased twofold in the lamella of HGF-treated cells but unchanged in the retraction tail, demonstrating that microtubule turnover is regionally regulated.     

PALAEOBIOLOGY OF THE CLIMACTICHNITES TRACEMAKER

Abstract:  Trace fossils such as Climactichnites offer rare insights into the palaeobiology of Cambrian soft-bodied animals, especially those that inhabited emergent sand flats and are not known from body fossils. Analysis of field and museum Climactichnites , together with experiments on the preservation of similar modern trails, indicates that the tracemaker was an elongate, bilaterally symmetrical, dorsoventrally flattened, soft-bodied animal with a muscular foot. These characteristics are consistent with the tracemaker being a primitive mollusc or mollusc-like animal. Unlike most Neoproterozoic and Cambrian molluscs, the tracemaker could reach considerable size; at up to c . 69 cm long, it was one of the largest Cambrian animals of its time. When moving on the sediment surface, locomotion resulted from muscular waves generated along the sole of its flexible foot; the foot was extended and then clamped onto the substrate. Contraction of pedal muscles then pulled the body forward. Sedimentary structures associated with Climactichnites  wilsoni , such as polygonal desiccation cracks, raindrop impressions, adhesion structures and gas escape structures demonstrate that the animal inhabited intermittently subaerially exposed environments. The tracemaker's method of locomotion is similar to that employed by modern intertidal gastropods, which make Climactichnites -like trails on exposed sand flats. However, these modern trails are not preserved because of erosion by wind, waves, tides and subsequent bioturbation. Abundant microbial sedimentary structures are associated with C. wilsoni , and together with low levels of vertical bioturbation, intimate that microbial binding may have mediated the preservation of these early mollusc trails.     

Analysis of lateral redistribution of a plasma membrane glycoprotein- monoclonal antibody complex [corrected] [published erratum appears in J Cell Biol 1988 Apr;106(4):following 1403]

The lateral redistribution of a major murine glycoprotein, GP80, was studied on locomoting fibroblasts, using rhodamine-conjugated mAbs and ultralow light level digitized fluorescence microscopy. Confirming an earlier study (Jacobson, K., D. O'Dell, B. Holifield, T.L. Murphy, and J. T. August. 1984. J. Cell Biol. 99:1613-1623), the distribution of GP80 was coupled with cell locomotion; motile cells exhibited a gradated distribution of the GP80-mAb complex over the cell surface, increasing from the front to the rear, whereas stationary cells exhibited a nearly uniform GP80 distribution. By monitoring locomoting single cells, we found the gradated fluorescence distribution to be maintained as an approximate steady state. Newly extended leading edges were almost devoid of the fluorescence labeling. This was strikingly demonstrated in prechilled cells in which the extension of fluorescence-free leading edges caused a pronounced boundary between fluorescent and nonfluorescent zones. Subsequently this boundary eroded gradually in a manner consistent with diffusional relaxation. Evidence indicated that the GP80 redistribution was primarily caused by the lateral motion of GP80 in the plasma membrane and not via intracellular membrane traffic. Two cell locomotion models which, in principle, could account for the GP80 redistribution were tested: the retrograde lipid flow (RLF) model (Bretscher, M. S., 1984. Science (Wash. DC). 224:681-686) and an alternative hypothesis, the retraction-induced spreading (RIS) model. The predictions of these models were stimulated by computer and compared with experiment to assess which model was more appropriate. Whereas both models predicted steady-state gradients similar to the experimental result, only the RIS model predicted the lack of retrograde movement of the fluorescent boundary.     

Mechanics of torque generation during quadrupedal arboreal locomotion

Quadrupedal animals moving on arboreal substrates face unique challenges to maintain stability. The torque generated by the limbs around the long axis of a branch during locomotion may clarify how the animals remain stable on arboreal supports. We sought to determine what strategy gray short-tailed opossums (Monodelphis domestica) use to exert torque and avoid toppling. The opossums moved across a branch trackway about half the diameter of their bodies. Part of the trackway was instrumented to measure substrate reaction forces and torque around the long axis of the branch. Kinematic analysis was used to estimate the center of pressure of the manus and pes; from center of pressure and vertical and mediolateral forces, the torque generated by substrate reaction forces versus muscular effort could be determined. Forelimbs generated significantly greater torque than hindlimbs, which is probably explained by the greater weight-bearing role of the forelimbs. Fore- and hindlimbs generated torque in opposite directions because contralateral fore- and hindlimbs typically contacted the branch. Torque generated by muscular effort, however, was often in the same direction in both fore- and hindlimbs. The muscle-generated torque is likely the result of mediolateral movement of the center of mass caused by mediolateral undulation of the torso. These results bear an important implication for the study of arboreal locomotion: center of mass dynamics are at least as important as static positions. M. domestica is a good representative for a primitive mammal, and comparisons with arboreal specialists will shed light on how proficient arboreal locomotion evolved.     

Functional morphology of the ear in fossorial rodents, Microtus arvalis and Arvicola terrestris

Functionally relevant features and parameters of the outer, middle, and inner ear were studied morphologically and morphometrically in two species of voles, smaller Microtus arvalis and larger Arvicola terrestris. The findings in these fossorial (i.e., burrowing) rodents with components of surface activity were compared with respective findings reported for taxonomically related muroid rodents representing the same size classes but different eco-morphotypes: obligate subterranean rodents (Ellobius talpinus and Spalax ehrenbergi superspecies) and generalized rodents (Mus domesticus and Rattus norvegicus). The ear in voles was characterized by traits reported for subterranean rodents. The eardrum was round, without a distinct pars flaccida, and had an area of 5.4 mm2 in M. arvalis and 9 mm2 in A. terrestris. The middle ear exhibited reduced goniale, enlarged incus nearly parallel to the manubrium of the malleus. The malleus-incus lever ratio amounted to 2.1 (M. arvalis) and 2.0 (A. terrestris). The malleus-incus complex weighed about 0.8 mg in both vole species. The stapedial footplate had an area of 0.3 mm2 in M. arvalis and 0.4 mm2 in A. terrestris. The cochlea had 2.3 coils in both vole species; the basilar membrane was 8.5 mm and 10.5 mm long in M. arvalis and A. terrestris, respectively. There were on average 1,030 (M. arvalis) and 1,220 (A. terrestris) inner hair cells, and 3,760 (M. arvalis) and 4,250 (A. terrestris) outer hair cells in the organ of Corti. In quantitative terms, all these (as well as some further) traits and parameters were intermediate (related to body size) between those reported for generalized rodents on the one hand and subterranean ones on the other. The sound transmission system of the ear seems to be best tuned to frequencies of about 8-16 kHz with a high-frequency cut-off at about 50-60 kHz. The ear of A. terrestris seems to be tuned to somewhat lower frequencies than that in M. arvalis. In this aspect as well as regarding hearing sensitivity (as judged from the mechanical transmission parameters), voles can be considered intermediate not only in their lifestyle but also in their hearing abilities between the subterranean rodents (mole-vole and blind mole-rat) and the surface dwellers (house mouse and Norway rat).     

Hindlimb morphology and locomotor performance in waders: an evolutionary approach

Locomotion performance (measured as stride frequency and stride length) was studied in 16 species of waders. Differences in hindlimb morphology (osteology and myology) were analysed among species. Evolutionary changes in both locomotion and morphological variables were analysed using comparative methods revealing the existence of some ecomorphological patterns relating these two sets of characters. Evolutionary changes in stride frequency were correlated with changes in the muscles M. iliotibialis cranialis, M. iliotibiales lateralis and M. gastrocnemius, whereas changes in stride length showed correlated evolution with changes in the length of distal segments of the leg. We identify two different evolutionary strategies in locomotion of waders. One is a change in distal leg segments (skeletal system), an adaptive modification that increases stride length; the second is a change in the skeletal-muscular system, providing an increase in muscular performance (force or speed of contraction) in several muscles, and is an adaptation that increases stride frequency.     

Patterns in the change in the number of carriers and epizootic activity in a floodplain local natural focus of tularemia in Voronezh Province]

Prolonged study of the population of Arvicola terrestris L. in connection with tularemia epizootic among these animals showed this animal to serve as the principal carrier of tularemia infection in the Povorinsk natural focus. Epizootics proved to originate with a definite threshold count of Arvicola terrestris L.; this threshold constituted about 30% of the trapped animals. Dynamics of the epizootic activity was characterized by alterations of cycles of various duration, coursing by waves, with 2--3-year periods. Reduction of the epizootic intensity coursed during a decade in 2 waves with 3-year periods, and during a 7-year period--in one 3-year wave. During the epizootics with the character of a 2-year wave the population of the principal carrier diminished, and with a 3-year wave the count of Arvicola terrestris L. decreased during the first year, and began to increase during the second year, despite the persistence of the epizootic. Detection of regularities attending the changes in the population of the principal carrier of the infection and its connection with the epizootics permitted to make long-period prognoses of the epizootic activity and to plan antiepidemic measures in the focus.     

Conservation rules, their breakdown, and optimality in Caenorhabditis sinusoidal locomotion

Undulatory locomotion is common to nematodes as well as to limbless vertebrates, but its control is not understood in spite of the identification of hundred of genes involved in Caenorhabditis elegans locomotion. To reveal the mechanisms of nematode undulatory locomotion, we quantitatively analysed the movement of C. elegans with genetic perturbations to neurons, muscles, and skeleton (cuticle). We also compared locomotion of different Caenorhabditis species. We constructed a theoretical model that combines mechanics and biophysics, and that is constrained by the observations of propulsion and muscular velocities, as well as wavelength and amplitude of undulations. We find that normalized wavelength is a conserved quantity among wild-type C. elegans individuals, across mutants, and across different species. The velocity of forward propulsion scales linearly with the velocity of the muscular wave and the corresponding slope is also a conserved quantity and almost optimal; the exceptions are in some mutants affecting cuticle structure. In theoretical terms, the optimality of the slope is equivalent to the exact balance between muscular and visco-elastic body reaction bending moments. We find that the amplitude and frequency of undulations are inversely correlated and provide a theoretical explanation for this fact. These experimental results are valid both for young adults and for all larval stages of wild-type C. elegans. In particular, during development, the amplitude scales linearly with the wavelength, consistent with our theory. We also investigated the influence of substrate firmness on motion parameters, and found that it does not affect the above invariants. In general, our biomechanical model can explain the observed robustness of the mechanisms controlling nematode undulatory locomotion.     

Cell surface receptors transmit sufficient force to bend collagen fibrils

To better understand the dynamic interaction of cells with their surrounding extracellular matrix, chondrocytes and rat embryo fibroblasts were overlaid with individual collagen fibrils and observed with high-resolution video-enhanced differential interference contrast microscopy. Although the cells had a polygonal shape characteristic of nonmotile cells, they used processes usually associated with cell locomotion to acquire the collagen fibrils. Instead of being transported in a retrograde direction, fibrils on the dorsal cell surface were bent, and regions of the bent fibrils were shifted in diverse directions. A blocking antibody to the beta1 integrin subunit significantly inhibited collagen fibril acquisition and bending. Enhanced actin assembly was only occasionally associated with fibrils undergoing rearrangement. Considering that the relatively stiff collagen fibrils require the application of force to be bent, this study shows that cells with a polygonal morphology (as opposed to a polarized, motile shape) are capable of exerting force through the beta1 integrins on the dorsal surface of the cell. Analysis of the bending patterns indicates that fibril buckling was induced by retrograde force combined with regions held stationary and/or the fibrils were bent by forces acting in opposing directions.     

Analysis of the Actin–Myosin II System in Fish Epidermal Keratocytes: Mechanism of Cell Body Translocation

While the protrusive event of cell locomotion is thought to be driven by actin polymerization, the mechanism of forward translocation of the cell body is unclear. To elucidate the mechanism of cell body translocation, we analyzed the supramolecular organization of the actin–myosin II system and the dynamics of myosin II in fish epidermal keratocytes. In lamellipodia, long actin filaments formed dense networks with numerous free ends in a brushlike manner near the leading edge. Shorter actin filaments often formed T junctions with longer filaments in the brushlike area, suggesting that new filaments could be nucleated at sides of preexisting filaments or linked to them immediately after nucleation. The polarity of actin filaments was almost uniform, with barbed ends forward throughout most of the lamellipodia but mixed in arc-shaped filament bundles at the lamellipodial/cell body boundary. Myosin II formed discrete clusters of bipolar minifilaments in lamellipodia that increased in size and density towards the cell body boundary and colocalized with actin in boundary bundles. Time-lapse observation demonstrated that myosin clusters appeared in the lamellipodia and remained stationary with respect to the substratum in locomoting cells, but they exhibited retrograde flow in cells tethered in epithelioid colonies. Consequently, both in locomoting and stationary cells, myosin clusters approached the cell body boundary, where they became compressed and aligned, resulting in the formation of boundary bundles. In locomoting cells, the compression was associated with forward displacement of myosin features. These data are not consistent with either sarcomeric or polarized transport mechanisms of cell body translocation. We propose that the forward translocation of the cell body and retrograde flow in the lamellipodia are both driven by contraction of an actin–myosin network in the lamellipodial/cell body transition zone.     

Entamoeba motility: dynamics of cytoplasmic streaming, locomotion and translocation of surface-bound particles, and organization of the actin cytoskeleton in Entamoeba invadens.

The dynamics of cytoplasmic streaming, retrograde translocation of externally bound particles and locomotion by Entamoeba invadens were compared. Locomoting amoebae were monopodial, exhibited fountain flow cytoplasmic streaming and translocated externally bound erythrocytes to the rear of cells. The rates of rearward flow of peripheral cytoplasmic vacuoles and of the externally bound particles were equal to the rate of cell forward locomotion. Rhodamine-phalloidin staining revealed a distinct cortical polymerized actin cytoskelton. This was least evident about the periphery of the advancing pseudopod, increased in density toward the rear of the cell and was most concentrated in the uroid. A monoclonal anti-eucaryotic actin antibody, which recognized monomeric Entamoeba actin on immunoblots, stained trophozoites by indirect immunofluorescence throughout the cytoplasm, but not in the cortical regions stained by rhodamine-phalloidin. This and other evidence implied that the antibody recognized only unpolymerized actin in Entamoeba. We propose that locomotion, cytoplasmic streaming and translocation of externally bound particles are driven by a common actin-based mechanism in Entamoeba, possibly involving retrograde cortical actin flow and recycling.     

The fine structure of conidial development in the genus Torula. II. T. caligans (Batista and Upadhyay) M. B. Ellis and T. terrestris Mistra.

Conidia of Torula caligans (Batista & Upadhyay) M. B. Ellis comb.nov. and T. terrestris Misra were examined by transmission- and scanning-electron microscopy. Torula caligans produced four-celled conidia in which the central cells were distinctly larger than the basal and apical cells. Conidia of T. terrestris were 4- to 7-celled long and ellipsoidal in shape. Conidiogenous cells in both species developed melanin only within the lowermost part of the lateral walls while the other cells of the conidium were uniformly melanized around the circumference of the cell; melanin in these cells being deposited within, at least, half the width of the cell wall. In both species new conidia arose from evagination of the hyaline apex of the conidiogenous cell and are therefore blastoconidia. The systematic relationships between T. caligans and T. terrestris and other species of the genus Torula are discussed.     

Entamoeba Motility: Dynamics of Cytoplasmic Streaming, Locomotion and Translocation of Surface-Bound Particles, and Organization of the Actin Cytoskeleton in Entamoeba invadens

ABSTRACT. The dynamics of cytoplasmic streaming, retrograde translocation of externally bound particles and locomotion by Entamoeba invadens were compared. Locomoting amoebae were monopodial, exhibited fountain flow cytoplasmic streaming and translocated externally bound erythrocytes to the rear of cells. The rates of rearward flow of peripheral cytoplasmic vacuoles and of the externally bound particles were equal to the rate of cell forward locomotion. Rhodamine-phalloidin staining revealed a distinct cortical polymerized actin cytoskeleton. This was least evident about the periphery of the advancing pseudopod, increased in density toward the rear of the cell and was most concentrated in the uroid. A monoclonal anti-eucaryotic actin antibody, which recognized monomeric Entamoeba actin on immunoblots, stained trophozoites by indirect immunofluorescence throughout the cytoplasm, but not in the cortical regions stained by rhodamine-phalloidin. This and other evidence implied that the antibody recognized only unpolymerized actin in Entamoeba . We propose that locomotion, cytoplasmic streaming and translocation of externally bound particles are driven by a common actin-based mechanism in Entamoeba , possibly involving retrograde cortical actin flow and recycling.     

Tracking retrograde flow in keratocytes: news from the front

Actin assembly at the leading edge of the cell is believed to drive protrusion, whereas membrane resistance and contractile forces result in retrograde flow of the assembled actin network away from the edge. Thus, cell motion and shape changes are expected to depend on the balance of actin assembly and retrograde flow. This idea, however, has been undermined by the reported absence of flow in one of the most spectacular models of cell locomotion, fish epidermal keratocytes. Here, we use enhanced phase contrast and fluorescent speckle microscopy and particle tracking to analyze the motion of the actin network in keratocyte lamellipodia. We have detected retrograde flow throughout the lamellipodium at velocities of 1-3 microm/min and analyzed its organization and relation to the cell motion during both unobstructed, persistent migration and events of cell collision. Freely moving cells exhibited a graded flow velocity increasing toward the sides of the lamellipodium. In colliding cells, the velocity decreased markedly at the site of collision, with striking alteration of flow in other lamellipodium regions. Our findings support the universality of the flow phenomenon and indicate that the maintenance of keratocyte shape during locomotion depends on the regulation of both retrograde flow and actin polymerization.     

The effect of alkaline earth cations and of ionic strength on the dissociation of earthworm hemoglobin at alkaline pH

1. The effect of alkaline earth cations on the dissociation of the extracellular hemoglobin of Lumbricus terrestris and the effect of ionic strength on the dissociation of the hemoglobins of L. terrestris and Tubifex tubifex at concentrations of ca 2.5 mg/ml, over the pH range 9.0-10.5 was investigated using ultracentrifugation to separate the dissociated from the undissociated molecules. 2. Mg(II), Ca(II) and Sr(II) at concentrations of up to 0.2 M, decreased the dissociation of Lumbricus oxyhemoglobin from 70% at pH 9.0 and 100% at pH 9.5 and higher, to 20-30% at 0.05 M. The three cations were equally effective in decreasing the extent of dissociation of L. terrestris oxyhemoglobin over the pH range 9.0-10.5, with a K1/2 of ca 10 mM. 3. The dissociation of L. terrestris oxyhemoglobin over the pH range 9.0-10.5 was decreased only to 50-60% in the presence of up to 0.5 M NaCl or KCl; there was no further decrease in dissociation at concentrations of the two salts up to 1.5 M. 4. The dissociation of T. tubifex oxyhemoglobin over the pH range 9.0-10.0 was decreased from 100% to ca 40-50% in the presence of 0.5 M NaCl or KCl with little or no change at higher concentrations. At pH 10.5 and 11.0 the decrease in dissociation was more gradual, reaching ca 50% at 1.5 M NaCl.     

The burrowing of Priapulus caudatus

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