Machaeridian locomotion

The discovery that machaeridians (class Machaeridia Withers, 1926) are annelids allows their mode of locomotion to be interpreted in the context of the body plan of this phylum. The Plumulitidae were errant epibenthic forms, moving with parapodia. The body of Turrilepadidae and Lepidocoleidae, however, was enclosed largely within the mineralized plates that make up the skeleton. Articulated specimens indicate that these machaeridians were able to burrow like other annelids using peristaltic locomotion. A lepidocoleid specimen indicates that multiple waves of shortened and contracted regions moved over the body. This is in contrast to the mode of locomotion in earthworms and most polychaetes, but similar to peristaltic progression in Polyphysia (Scalibregmidae). Either the rugose sculpture (turrilepadids) and/or the margins of the overlapping shell plates functioned as a burrowing sculpture, allowing forward movement but preventing backwards slipping. A trace from the Devonian Hunsrück Slate associated with a lepidocoleid indicates that considerable flexing of the skeleton was possible, but this is an escape trace and does not represent normal locomotion. Features of the skeleton of machaeridians are convergent on those of molluscs where the shells likewise function in protection and burrowing.     

A NEW TRAVERSODONTID CYNODONT (THERAPSIDA, EUCYNODONTIA) FROM THE MIDDLE TRIASSIC SANTA MARIA FORMATION OF RIO GRANDE DO SUL, BRAZIL

Abstract:  Remains of a peculiar traversodontid cynodont, Protuberum cabralensis gen. et sp. nov., are described herein. The material was collected from two outcrops representing the Therapsid Cenozone (Middle Triassic) of the Santa Maria Formation, and consists of a cranium with most of its dentition preserved and an associated postcranial skeleton. The upper postcanines have two sharp cusps that are connected by a medial crest on unworn postcanines. The specimens possess several autapomorphies, including: (1) presence of thickened bone on the dorsal surface of the skull; (2) thick dorsal ribs, with remarkable processes situated on their dorsal borders that decrease in size distally; and (3) an iliac blade with a series of rugosities along its dorsal border. The lumbar ribs bear overlapping costal plates and have distally projecting rib shafts that differ from the pattern observed in Thrinaxodon , Pascualgnathus and Cynognathus .     

GROWTH PATTERNS OF THRINAXODON LIORHINUS, A NON-MAMMALIAN CYNODONT FROM THE LOWER TRIASSIC OF SOUTH AFRICA

Abstract:  The growth dynamics of the Early Triassic non-mammalian cynodont Thrinaxodon liorhinus were assessed through bone histology. Several limb bones of various sizes were examined, revealing a rapidly deposited, uninterrupted, fibro-lamellar bone tissue. A region of slowly deposited parallel-fibred bone occurs peripherally in most skeletal elements studied, becoming more extensively developed in the larger limb bones. On the basis of the bone histology, it is proposed that Thrinaxodon liorhinus grew rapidly during early ontogeny, and at a slower rate with increasing age, possibly once sexual maturity was reached. Variation in bone tissue patterns at different stages of ontogeny is noted and discussed. Given that growth rings are generally absent from the skeletal elements studied, and that the environment was seasonal, it appears that Thrinaxodon liorhinus growth was unaffected by environmental fluctuations.     

Nocturnality in synapsids predates the origin of mammals by over 100 million years

Nocturnality is widespread among extant mammals and often considered the ancestral behavioural pattern for all mammals. However, mammals are nested within a larger clade, Synapsida, and non-mammalian synapsids comprise a rich phylogenetic, morphological and ecological diversity. Even though non-mammalian synapsids potentially could elucidate the early evolution of diel activity patterns and enrich the understanding of synapsid palaeobiology, data on their diel activity are currently unavailable. Using scleral ring and orbit dimensions, we demonstrate that nocturnal activity was not an innovation unique to mammals but a character that appeared much earlier in synapsid history, possibly several times independently. The 24 Carboniferous to Jurassic non-mammalian synapsid species in our sample featured eye morphologies consistent with all major diel activity patterns, with examples of nocturnality as old as the Late Carboniferous (ca 300 Ma). Carnivores such as Sphenacodon ferox and Dimetrodon milleri, but also the herbivorous cynodont Tritylodon longaevus were likely nocturnal, whereas most of the anomodont herbivores are reconstructed as diurnal. Recognizing the complexity of diel activity patterns in non-mammalian synapsids is an important step towards a more nuanced picture of the evolutionary history of behaviour in the synapsid clade.     

A new galesaurid (Therapsida: Cynodontia) from the Lower Triassic of South Africa

A new galesaurid cynodont, Progalesaurus lootsbergensis gen. et sp. nov., is described on the basis of a well-preserved skull, lower jaw, right scapula and left atlantal neural arch. Autapomorphies of Progalesaurus include postcanine teeth bearing numerous mesial and distal accessory cusps that flank a recurved main cusp, a post-temporal fenestra bordered by the squamosal ventrally and a large external naris. Progalesaurus is similar to Galesaurus in possessing a poorly defined masseteric fossa on the dentary, a strongly recurved main cusp of the postcanine dentition, an incomplete secondary palate and a similar basisphenoid-parasphenoid morphology. A cladistic analysis of ten early cynodont genera resolves a monophyletic Galesauridae encompassing Cynosaurus , Progalesaurus and Galesaurus , although support for this clade is weak. Procynosuchus and Dvinia are placed at the base of Cynodontia whereas Thrinaxodon and Platycraniellus are positioned higher, but outside of Eucynodontia. The holotype and only known specimen of Progalesaurus was collected during systematic prospecting of Permo/Triassic boundary strata at New Lootsberg Pass, Graaff-Reinet District, South Africa. The discovery of Progalesaurus increases the number of valid Early Triassic cynodonts to four and sheds light on the tempo of early cynodont diversification after the end-Permian mass extinction.     

Push and bite: trade‐offs between burrowing and biting in a burrowing skink (Acontias percivali)

Trade‐offs are thought to be important in constraining evolutionary divergence, as they may limit phenotypic diversification. Limbless animals that burrow head‐first have been suggested to be evolutionarily constrained in the development of a large head size and sexual head shape dimorphism because of potential trade‐offs associated with burrowing. Here we use an acontiine skink (Acontias percivali) to test for the existence of trade‐offs between traits thought to be important in burrowing (speed and force). As head size dimorphism has been shown to be limited in acontiine lizards, thus suggesting constraints on head size and shape, we additionally explore the potential for trade‐offs between burrowing and biting. Our data show that A. percivali uses a burrowing style different from those previously described for caecilians and amphisbaenians, which relies on the use of extensive lateral and dorsoventral head movements. Our data also show that animals use their entire bodies to generate force, as peak force was determined by total length only. Additionally, both bite force and the time needed to burrow into the substrate were principally determined by relative head width, suggesting a trade‐off between biting and burrow speed. Performance data were indeed suggestive of a correlation between bite force and the time needed to burrow, but additional data are needed to confirm this pattern. In summary, our data suggests that trade‐offs may exist, and may have been of crucial importance in shaping the evolution of head shape in A. percivali, and burrowing lizards more generally. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 91–99.     

Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi‐arid climate?

Krapovickas, V., Mancuso, A.C., Marsicano, C.A., Domnanovich, N.S. & Schultz, C.L. 2013: Large tetrapod burrows from the Middle Triassic of Argentina: a behavioural adaptation to seasonal semi‐arid climate? Lethaia, Vol. 46, pp. 154–169. We report the discovery of large burrow casts in the early Middle Triassic Tarjados Formation, at Talampaya National Park, north‐western Argentina. Facies analysis indicates the burrows are preserved in sandbars deposited by an ephemeral river under semi‐arid and seasonal climatic conditions. The structures are mostly preserved in longitudinal cross‐section and consist of an opening, an inclined tunnel (ramp), and a terminal chamber. The ramp is 8–14 cm in height, up to 130 cm in length and penetrates 49–63 cm bellow the palaeosurface with an inclination of 22°–30°. We studied burrow cast dimensions, overall architectural morphology, surficial marks, and compared them with other large burrows of both invertebrate and vertebrate origin. A tetrapod origin of the burrow casts was established based on: distinctive architecture, and size, which is more than twice the most common size range for large terrestrial invertebrate burrows. Comparison with other Upper Permian and Triassic tetrapod burrows allows us to identify three general morphological groups: (1) simple inclined burrows; (2) helical burrows; and (3) burrow network complexes, representing different behaviours. A study of tetrapod body fossils preserved within other Upper Permian and Triassic burrows shows that the Tarjados structures were most likely produced by non‐mammalian cynodonts. The environmental and climatic context suggests that aridity and seasonality played a fundamental role selecting burrowing behaviour in therapsids and that by the Early–Middle Triassic their burrowing behaviour attained a complexity comparable to modern mammals. □Argentina, behaviour, palaeoclimate, Permo‐Triassic, Tarjados Formation, Tetrapod burrows.     

Burrow morphology and utilization of the goby (Parapocryptes serperaster) in the Mekong Delta,Vietnam

Some fish species living in mudflats construct burrows for dwelling and hiding. The goby Parapocryptes serperaster is a burrowing fish in mudflats of many estuaries in South East Asia. This study was carried out in the Mekong Delta, Vietnam, to examine burrow morphology and usage by this species. Morphology of the burrows constructed by P. serperaster was investigated by resin castings in situ to obtain the physical structure and configuration of each burrow. Fish from the burrows were caught and measured before burrow casts were made. Fish burrows comprised several openings, a few branching tunnels and multi-bulbous chambers. The surface openings were circular, and the shapes of branching tunnels were nearly round. The burrows had interconnected tunnels and various short cul-de-sac side branches. The burrow structure differed between fish sizes, but burrow dimensions were positively correlated with fish size, indicating that larger fish can make larger and more sophisticated burrow. The burrow structure and dimensions were not different between the dry and wet seasons. Laboratory observations showed that P. serperaster used body movements to dig burrows in the sediment. Burrows could provide a low-tide retreat and protection from predators, but were not used for spawning and feeding for this goby species. This study indicates that the burrowing activity of gobies is an important adaptation for living in shallow and muddy habitats.     

Burrow structure and foraging costs in the fossorial rodent,Thomomys bottae

Summary A model for calculating the energy cost of burrowing by fossorial rodents is presented and used to examine the energetics of foraging by burrowing. The pocket gopher Thomomys bottae (Rodentia: Geomyidae) digs burrows for access to food. Feeding tunnels of Thomomys are broken into segments by laterals to the surface that are used to dispose of excavated soil. Energy cost of burrowing depends on both soil type and on burrow structure, defined by the length of burrow segments, angle of ascent of laterals, depth of feeding tunnels, and burrow diameter. In a desert scrub habitat, Thomomys adjust burrow segment length to minimize cost of burrowing. Observed segment lengths (mean=1.33 m) closely approximate the minimum-cost segment length of 1.22 m. Minimizing energy expended per meter of tunnel constructed maximizes efficiency of foraging by burrowing in the desert scrub. Burrow diameter and cost of burrowing increase with body size, while benefits do not, so foraging by burrowing becomes less enconomical as body size increases. Maximum possible body size of fossorial mammals depends on habitat productivity and energy cost of burrowing in local soils.     

The occupation of artificial burrows by Helice tridens (De Haan) and the length of its stay

The mud-crab Helice tridens (De Haan) influences the cycling of matter in salt-marsh ecosystems through its burrowing activity. If the crabs occupy and stay in their burrows for a short time, their burrowing activity will be great, since they will continuously construct new burrows. Therefore, investigation of the relation between the crabs and their burrows is considered to be important. In the present study, the relation between pipes as a form of artificial burrow and their occupation by the crab was analyzed. A close relationship was recognized between the diameter of the pipe opening and the carapace width of the crab which occupied the pipe, while pipes with a length shorter than the depth of the crab burrows were hardly occupied. These results indicate that the diameter and length of an artificial burrow affects the likelihood of its occupation by this species of crab. The length of the crab's stay in this type of artificial burrow was generally 1 day. This result may be related to the field observation that newly made burrows frequently collapse due to water current occurring through tidal action after the crabs have left.     

A versatile laboratory stream with examples of its use in the investigation of invertebrate behaviour

A versatile and simple laboratory stream was designed and used to investigate the burrowing activity of two insects in response to changes in water velocity and substrate type.Aphelocheirus aestivalis adults were unable to burrow into sand, however, a small proportion of juveniles did burrow in this substrate. The presence of sand in gravel reduced the burrowing success of adults. Steady increases in flow stimulated the burrowing response of both adults and juveniles on gravel and sandy gravel.Ephemera danica was unable to burrow in sand alone at the velocities used in the experiment. The presence of particles greater than 2 mm in diameter in the substrate appeared to be essential for successful burrowing under the test conditions. An increase in flow from 3 to 8 cm s^–1 resulted in an increase in burrowing. The time taken for each specimen to burrow varied widely within replicate tests but most specimens had penetrated the substrate within 150 seconds of introduction. The implications of these observations in influencing the microdistribution of these species are discussed.     

Cyclaster danicus, a shallow burrowing non-marsupiate echinoid

The spatangoid Cyclaster danicus has been placed in the genus Brissopneustes by previous authors. The material from the Lower Danian of Denmark includes some abnormal individuals with depressed apical area. These have been previously interpreted as females with a marsupium. A study of both normal and abnormal tests indicates that the depressed apical area is not a marsupium but rather a malformation, possibly caused by adverse environmental conditions or by a parasite. The skeletal morphology indicates that C. danicus was a shallow burrowing form but the malformed individuals probably did not burrow.     

First trace and body fossil evidence of a burrowing, denning dinosaur

A fossil discovery in the mid-Cretaceous Blackleaf Formation of southwest Montana, USA, has yielded the first trace and body fossil evidence of burrowing behaviour in a dinosaur. Skeletal remains of an adult and two juveniles of Oryctodromeus cubicularis gen. et sp. nov. a new species of hypsilophodont-grade dinosaur, were found in the expanded distal chamber of a sediment-filled burrow. Correspondence between burrow and adult dimensions supports Oryctodromeus as the burrow maker. Additionally, Oryctodromeus exhibits features of the snout, shoulder girdle and pelvis consistent with digging habits while retaining cursorial hindlimb proportions. Association of adult and young within a terminal chamber provides definitive evidence of extensive parental care in the Dinosauria. As with modern vertebrate cursors that dig, burrowing in Oryctodromeus may have been an important adaptation for the rearing of young. Burrowing also represents a mechanism by which small dinosaurs may have exploited the extreme environments of polar latitudes, deserts and high mountain areas. The ability among dinosaurs to find or make shelter may contradict some scenarios of the Cretaceous-Paleogene impact event. Burrowing habits expand the known range of nonavian dinosaur behaviours and suggest that the cursorial ancestry of dinosaurs did not fully preclude the evolution of different functional regimes, such as fossoriality.     

Cranial structure and relationships of the Liassic mammal Sinoconodon*

The skull of the 'Rhaeto-Liassic' mammal Sinoconodon changchiawaensis (Young) from the lower Lufeng Series of China is described. It is characterized by a relatively larger and more robust dentary condyle and a greater reduction of the post-dentary bones than are present in the Morganucodontidae, Kuehneotheriidae, and Dinnetherium. In other aspects Sinoconodon is more primitive; precise post-canine occlusion is lacking, the mandibular symphysis is deep, the jaw articulation lies below a line projected through the apices of the teeth, the pterygoparoccipital foramen is large and the post-canine teeth cannot be divided into molars and premolars. The jaw articulation and braincase of Sinoconodon are compared with those of the two cynodont therapsids Probainognathus and Thrinaxodon. It is concluded that in the transition from therapsid to mammal the medial surface of the groove in the squamosal housing the quadrate was lost and, as a result, in Sinoconodon, Morganucodon and Dinnetherium the hollow medial surface of the quadrate abutted directly against the paroccipital process. A definition for the Class Mammalia is given. It is suggested that the three-boned middle ear was present in Cretaceous triconodonts, and that it probably arose independently in the lines leading to multituberculates and Cretaceous therians. The structure of recently discovered 'Rhaeto-Liassic' mammals and that of Sinoconodon indicates that there was greater diversity among the earliest known mammals than was previously thought.     

Application of morphologic burrow interpretations to discern continental burrow architects: Lungfish or crayfish?

A methodology for trace fossil identification using burrowing signatures is tested by evaluating ancient and modern lungfish and crayfish burrows and comparing them to previously undescribed burrows in a stratigraphic interval thought to contain both lungfish and crayfish burrows. Permian burrows that bear skeletal remains of the lungfish Gnathorhiza, from museum collections, were evaluated to identify unique burrow morphologies that could be used to distinguish lungfish from crayfish burrows when fossil remains are absent. The lungfish burrows were evaluated for details of the burrowing mechanism preserved in the burrow morphologies together forming burrowing signatures and were compared to new burrows in the Chinle Formation of western Colorado to test the methodology of using burrow signatures to identify unknown burrows.

Permian lungfish aestivation burrows show simple, nearly vertical, unbranched architectures and relatively smooth surficial morphologies with characteristic quasi‐horizontal striae on the burrow walls and vertical striae on the bulbous terminus. Burrow lengths do not exceed 0.5 m. In contrast, modern and ancient crayfish burrows exhibit simple to highly complex architectures with highly textured surficial morphologies. Burrow lengths may reach 4 to 5 m.

Burrow morphologies unlike those identified in Gnathorhiza aestivation burrows were found in four burrow groups from museum collections. Two of these groups exhibit simple architectures and horizontal striae that were greater in sinuosity and magnitude, respectively. One of these burrows contains the remains of Lysoro‐phus, but the burrow surface reveals no reliable surficial characteristics. It is not clear whether Lysorophus truly burrowed or merely occupied a pre‐existing structure. The other two groups exhibit surficial morphologies similar to those found on modern and ancient crayfish burrows and may provide evidence of freshwater crayfish in the Permian.

Burrows from the Upper Triassic Chinle Formation in western Colorado exhibit simple to moderately complex architectural morphologies, ranging from predominantly vertical, unbranched, with little or no chamber development to predominantly vertical, few branches, and with minor chamber development. Surficial burrow morphologies are moderate to highly textured. The burrows have scrape marks, scratch marks, mud and lag‐liners, knobby surfaces, pleopod striae, and body impressions.

Although no fossil remains of the burrowing organism were found within or associated with the Chinle burrows from western Colorado, the similarity of architectural and surficial burrow morphologies to those in the Chinle of Canyonlands, Utah and to modern crayfish burrows, clearly indicates that the Colorado burrows are the product of burrowing crayfish rather than lungfish. Evaluation of burrowing signatures preserved in the architectural and surficial burrow morphologies is a very useful tool to compare and contrast Chinle burrows from different regions on the Colorado Plateau. Documentation of crayfish burrows in the Chinle of Utah and Colorado strongly suggests that other large‐diameter Chinle burrows elsewhere on the Colorado Plateau and in stratigraphically equivalent units may also be the product of crayfish activity.     

Evolution of African mole-rat sociality: burrow architecture, rainfall and foraging in colonies of the cooperatively breeding Fukomys mechowii

African mole rats (Bathyergidae) offer an excellent system with which to test theories relating to the evolution and maintenance of sociality in mammals. The aridity food distribution hypothesis (AFDH) suggests that, within the bathyergids, sociality has evolved in response to patterns of rainfall, its effects on food distribution, and the subsequent costs and risks of foraging and dispersal. Here, in the first detailed study of burrow architecture in a social mole-rat species, with data from 32 burrows, we show that in the giant mole-rat Fukomys mechowii burrow fractal dimension increases with colony size and is higher during the rainy season than during the dry season. The mass of food in the burrow increases with fractal dimension and is higher during the rainy season than during the dry season. These results link for the first time colony size, burrow architecture, rainfall and foraging success and provide support for two assumptions of the AFDH, namely that (1) in arid conditions burrowing may be severely constrained by the high costs of digging; and (2) the potential risks of failing to locate food may be mitigated by increases in colony size.     

Correlation with a limited set of behavioral niches explains the convergence of somatic morphology in mygalomorph spiders

Understanding the drivers of morphological convergence requires investigation into its relationship with behavior and niche space, and such investigations in turn provide insights into evolutionary dynamics, functional morphology, and life history. Mygalomorph spiders (trapdoor spiders and their kin) have long been associated with high levels of morphological homoplasy, and many convergent features can be intuitively associated with different behavioral niches. Using genus-level phylogenies based on recent genomic studies and a newly assembled matrix of discrete behavioral and somatic morphological characters, we reconstruct the evolution of burrowing behavior in the Mygalomorphae, compare the influence of behavior and evolutionary history on somatic morphology, and test hypotheses of correlated evolution between specific morphological features and behavior. Our results reveal the simplicity of the mygalomorph adaptive landscape, with opportunistic, web-building taxa at one end, and burrowing/nesting taxa with structurally modified burrow entrances (e.g., a trapdoor) at the other. Shifts in behavioral niche, in both directions, are common across the evolutionary history of the Mygalomorphae, and several major clades include taxa inhabiting both behavioral extremes. Somatic morphology is heavily influenced by behavior, with taxa inhabiting the same behavioral niche often more similar morphologically than more closely related but behaviorally divergent taxa, and we were able to identify a suite of 11 somatic features that show significant correlation with particular behaviors. We discuss these findings in light of the function of particular morphological features, niche dynamics within the Mygalomorphae, and constraints on the mygalomorph adaptive landscape relative to other spiders.     

Three-dimensional morphology and palaeobiology of the trace fossil Dactyloidites jordii nov. isp. from the Carboniferous of England

The diverse ichnological assemblage from the outcrops near Howick (Northumberland, United Kingdom) is exceptionally well-preserved. Among these Carboniferous ichnotaxa is a new ichnospecies of Dactyloidites. Specimens were collected and processed using high-resolution serial grinding and photography to produce an accurate and precise three-dimensional model of these new burrows in full colour. The model produced in association with petrographic thin sections and field observations is used as the basis for comparison between Dactyloidites jordii nov. isp. and other ichnospecies of Dactyloidites. The current taxonomic status of the ichnogenus is examined and reviewed. D. jordii nov. isp. is a broadly bisymmetrical, stellate to palmate burrow composed of numerous long, narrow rays that exhibit three orders of branching arranged into tiered galleries radiating from a central shaft. The trace maker is suggested to be a vermiform organism with an adaptive burrowing strategy that facilitates alteration of its burrow construction to accommodate suboptimal sediment conditions. The adaptive nature of trace-making organisms and the inherent anisotropy of many burrowed media highlight the need for ichnologists to provide a type series rather than a single holotype, in order to capture the inherent range of common burrow morphologies.     

Is communal burrowing or burrow sharing a benefit of group living in the lesser cavy <Emphasis Type="Italic">Microcavia australis</Emphasis>?

Burrow systems play an important role in the life of rodents in arid environments. The objectives of this study were to examine the hypothesis that group living is beneficial to the semifossorial rodent, and determine whether Microcavia australis (Geoffroy and d’Orbigny, 1833) burrows communally and/or shares burrow systems. I related the structure of burrow systems to the number of cavies inhabiting them, in two habitats with different soil hardness and different plant cover (El Leoncito and Ñacuñán). El Leoncito has a harsh climate, with lower plant density and softer soil than Ñacñuán. A total of 18 burrow systems were characterized at Ñacuñán, and 12 at El Leoncito. Social groups at El Leoncito have a higher number of individuals than at Ñacuñán, but the structure of burrow systems in softer soil is narrower (small area size), with fewer holes, less slope and depth of galleries, and with no relationship between the number of holes and burrow area. Therefore, considering the development of the burrow system as an indicator of the cost of burrowing, I conclude that communal burrowing to reduce the energetic cost of burrowing per capita is not the primary cause of cavy sociality. M. australis were not active diggers, because digging behaviour was rarely recorded at either site. Burrow systems of cavies persisted over the years of study, occupied by the same cavies and new offspring, and digging new burrow systems and tunnels was a relatively rare event at both sites. Under the burrow-sharing hypothesis, sociality could prevail in M. australis that regularly dig to build and maintain a burrow system which they use for a long time.     

Responses of <Emphasis Type="Italic">Venerupis philippinarum</Emphasis> (Mollusca: Bivalvia) to Predators and Changes in Hydrodynamics

The rate of burrowing into sand by the bivalve mollusk Venerupis philippinarum was studied under laboratory conditions. It is found that an increase in the intensity of water flow to an average of 1000 ml/min stimulates the burrowing of the mollusk, while higher values suppress burrowing; the threshold values are somewhat different for the young and adult specimens. It is shown that the presence of the starfish Asterias amurensis in the experimental environment decreases the rate of burrowing of V. philippinarum by 10–20% depending upon the sizes of the predator and the potential victim, but the depth of penetration of the mollusks into the sediment increases. It is supposed that in V. philippinarum and other species of bivalve mollusks related to the same life form and characterized by a moderate capability to burrow into the ground, the adaptive strategy of threat avoiding (great wave activity, an approach of a predator) is expressed as burrowing into a depth uncommon for usual situations and waiting. This behavior, to a significant degree, provides the capability of some species to inhabit shallow water areas with poor hydrodynamics inhabited by numerous predators.