U-shaped Burrows Research Articles

Macrofauna on flood delta shoals in the Wadden Sea with an underground association between the lugwormArenicola marina and the amphipodUrothoe poseidonis

Living conditions for macrofauna on flood delta shoals are determined by surf, strong currents and sediment mobility. Thus, a unique assemblage of invertebrate species colonize these far off-shore, low intertidal flats. We here describe the macrobenthic fauna of emerging shoals in the Wadden Sea between the islands of Römö and Sylt. Besides ubiquitous macroinvertebrates of the intertidal zone and species which attain their main distribution in the subtidal zone, the flood delta shoals are characterized by organisms adapted to live in these highly unstable sediments, like the polychaetesSpio martinensis, Streptosyllis websteri, Magelona mirabilis, Psammodrilus balanoglossoides, the pericarid crustaceansCumopsis goodsiri, Tanaissus lilljeborgi, Bathyporeia sarsi and a few others. Average abundance (1440 m−2 of ind >1 mm) and biomass (12.9 g AFDW m−2) were low compared to other intertidal habitats in the Wadden Sea. Biomass was dominated by largesized individuals of the lugwormArenicola marina. The U-shaped burrows of these polychaetes were inhabited by high numbers ofUrothoe poseidonis. Maximum densities of these amphipods occurred in the deepest parts of the burrows. Sampling at approximately montly intervals revealed no apparent seasonality ofU. poseidonis abundance. Together with smallCapitella capitata, these amphipods constitute a deep-dwelling component of the macrofauna associated with lugworms, which is separated from all other macrofauna living at the sediment surface. As a response to rising sea level and increasing tidal ranges, we expect the unstable sandy shoals, inhabited by numerousSpio martinensis andUrothoe poseidonis, to expand within the Wadden Sea at the cost of stable sandy flats with abundant macrofauna.

Behaviour and tolerance to hypoxia in juvenile Norway lobster ( Nephrops norvegicus ) of different ages

The annual occurrence of hypoxia ( 80% oxygen saturation, pO2 > 16.7 kPa), moderate hypoxia (30% oxygen saturation, pO2 = 6.3 kPa) and hypoxia (25% oxygen saturation, pO2 = 5.2 kPa). The experiments were run for a maximum period of 24 h or until individuals died. Behaviour was studied using sequential video recordings of four behavioural activities: digging, walking, inactivity or flight (escape swimming up into the water column). Behaviour and mortality changed with lowered oxygen concentrations; energetically costly activities (such as walking) were reduced, and activity in general declined. In normoxia, juveniles initially walked and then burrowed, but when exposed to hypoxia they were mainly inactive with occasional outbursts of escape swimming. To increase oxygen availability the juveniles were observed to raise their bodies on stilted legs (similar to adults in hypoxic conditions), but oxygen saturations of 25% were lethal within 24 h. The results suggest that the main gas exchanges of early postlarval stages occur over the general body surface. Burrowing behaviour was tested in Postlarvae 1 and 2 of different ages held in >80% oxygen saturation for 1 wk. The difference in time taken to complete a V-shaped depression or a U-shaped burrow was measured. The results showed a strong negative relationship between postlarval age and burrowing time, but all individuals made a burrow. Juveniles were more sensitive to hypoxia than adults. Thus, the possible consequences of episodic hypoxia for the recruitment of Nephrops norvegicus and for the recolonization of severely affected areas are discussed.

Amino acid and metal content ofCrassostrea gigasshell infested byPolydorasp. in the prismatic layer insoluble matrix and blister membrane

Resume The spionid polychaete Polydora sp. can live and reproduce inside the oysters' shell, excavating a U-shaped burrow the central portion of which is filled with detritus and particles of dissolved shell. The oyster responds by secreting an organic layer, confining the worm, and later covering it with calcitostracum. This process creates a characteristic blister. Cra.s.sostrea gigus werc analysed for the organic matrix amino acid content and 14 metals of the whole shell of normal oystcrs and severely Polydora infested ones. Amino acid, DOPA and FI'-Raman analyses wcre also performed on isolated membranes from the characteristic mud blister and on prismatic layer insoluble matrix (PLIM) of infested oysters, with the aim of detecting any differences between the two organic matrices. Membranes and PLIM composition differ from whole normal shell organic matrix by having lower aspartate and glycine and higher levels of virtually al1 hydrophobic amino acids, especially alanine. There are no signifiant differences between membranes and PLIM in the ratio of charged to non-polar amino acids, respectively 0.54 and 0.59. L-DOPA content is also sirnilar in the two matrices with 0.45 (k0.18) and 0.57 (f 0.30) ng.rng-' protein for PLIM and membranes respectively. The FT-Raman spectra of membranes is very similar to that of PLIM, suggesting that they have identical composition. Zinc, iron and manganese are significantly higher in infested than in normal shells. Infested oysters can provide an excellent opportunity for investigating normal biological calcification processes.

Trace fossils indicating bottom aeration changes: Folusz Limestone, Oligocene, Outer Carpathians, Poland

Abstract Bioturbation sequences in the pelagic Folusz limestone indicate deposition under decreasing bottom aeration, possibly in association with the development of microbial mats. U-shaped burrows Diplocraterion and Arenicolites exclusively were produced in the laminated limestone, and they represent the only colonizers (sessile suspension feeders) of the oxygen-deficient sediment.

Commensalism of a Bivalve, Peregrinamor Ohshimai, With a Thalassinidean Burrowing Shrimp, Upogebia Major

Ecological, behavioural and anatomical observations of a commensal bivalve, Peregrinamor ohshimai (Mollusca: Galeommatoidea), were carried out in a tidal mudflat in the Seto Inland Sea, Japan. The bivalve attached specifically to the longitudinal groove of the ventral side of the cephalothorax of thalassinidean burrowing shrimps, Upogebia major and Lf. narutensis (Crustacea: Decapoda), singly, dorso-ventrally and longitudinally, using its byssus, with its anterior part towards the head of the host. The mantle of the commensal bivalve has wide anterior (branchio-pedal) and narrow posterior (exhalant) apertures. In the living organism, the extended anterior edges of the mantle protrude from the shell and are inserted into the host's filtering basket, which is formed by the setal rows of the first two pairs of pereiopods and utilized for intercepting suspended matter. By beating its pleopods in a U-shaped burrow, the filter-feeding Upogebia shrimp creates water currents, which are also utilized by the commensal bivalve for filter-feeding. The shell length of the commensal bivalve was in proportion to the host's carapace length. This suggests that the veliger larva attaches to a young host and grows, thus maintaining the host-commensal morphological matching. The bivalve is a hermaphrodite and individuals of >8–5 mm in shell length were already producing eggs. Anatomical observations suggest that P. ohshimai is most closely related to the Montacutidae in Galeommatoidea.

The burrows and physiological adaptations to a burrowing lifestyle of Natatolana borealis (Isopoda: Cirolanidae)

The isopod Natatolana borealis Lilljeborg constructs U-shaped burrows in soft mud, the bore of which closely approximates the width of the occupant. Within artificial burrows, the isopods are largely quiescent and often adopt a position close to one of the burrow openings. Conditions within burrows constructed in the laboratory are moderately hypoxic [11.7 to 14.9 kPa (88 to 112 torr)], with isopods showing discontinuous irrigation behaviour (pleopod beating). Rates of oxygen consumption \((\dot M_{O_2 } )\) (measured at 10°C) are maintained approximately constant over a wide range of oxygen partial pressure (PO2) due, in part, to a pronounced increase in pleopod beat rate. Values for the “critical” partial pressure of oxygen (Pc), the PO2 at which \(\dot M_{O_2 } \) can no longer be maintained independent of PO2, were 2.0 to 3.3 kPa (15 to 25 torr). N. borealis can survive lengthy periods (65 h at 5°C) of anoxia, during which there is a significant reduction in the carbohydrate concentration and an increase in the l-lactate concentration of the tissues. The oxygencarrying capacity of the haemolymph of N. borealis was low. The haemocyanin showed a relatively high oxygen affinity [P50=0.39 kPa (2.99 torr) at 10°C at the in vivo pH of 7.80] and a pronounced Bohr effect (-1.22). These characteristics may be advantageous to a burrowing mode of life and also for the conditions likely to be encountered in fish carcasses into which they burrow en masse to feed.

Aerobic Respiration during Sulfide Exposure in the Marine Echiuran WormUrechis caupo

Urechis caupo inhabit U-shaped burrows in mudflats where they are exposed to toxic hydrogen sulfide. During tidal exposure sulfide levels average 27μM and oxygen levels average 77 mmHg. The oxygen consumption rate (V̇o2) of U. caupo was measured at varying partial pressures of oxygen and with and without sulfide to investigate whether aerobic respiration is maintained during tidal exposure. Animals exposed to PO₂'s as low as 32 mmHg and sulfide concentrations of less than 30 μM did not significantly change V̇o2 (mean V̇o2 = 0.039 ± 0.016 mL O₂·g⁻¹·h⁻¹), although there was a general trend of increased V̇o2 with increased sulfide. We investigated whether this animal avoids sulfide toxicity by oxidation of sulfide catalyzed by coelomic fluid hematin. A positive correlation was found between V̇o2 and hematin concentration for animals exposed to 4-29 μM sulfide. The V̇o2 of coelomic fluid samples measured in vitro showed a peak V̇o2 and positive correlation with hematin concentration at 17 μM sulfide. Oxygen consumption rates of hematin isolated from the coelomic fluid showed a positive correlation between V̇o2 and sulfide concentration at 1.0 and 1.8 mM hematin, and V̇o2 was significantly greater at 1.8 mM hematin in the presence of sulfide. These results suggest that oxygen consumption in U. caupo is not inhibited at environmental oxygen and sulfide levels and that the elevation in V̇o2 observed in the presence of sulfide in vitro may be due to oxidation of sulfide by coelomic fluid hematin.

Morphological adaptations of the respiratory hindgut of a marine echiuran worm.

The echiuran worm Urechis caupo lives in U-shaped burrows in marine mudflats where levels of toxic hydrogen sulfide increase and water becomes hypoxic during low tide. Even in this low oxygen and high sulfide environment, the animal is capable of maintaining aerobic respiration. Gas exchange occures across both the body wall and hindgut. The hindgut functions as a type of water lung and is a thin walled, highly convoluted structure capable of considerable dilatation. It is rhythmically ventilated with water and its role as a respiratory organ becomes increasingly important as ambient pO2 drops. In the deflated hindgut light microscopy reveals a pseudostratified appearing innermost mucosal epithelium composed of columnar cells with nuclei at different levels. When the hindgut is fully inflated, ultrastructural studies show a simple columnar epithelium with the nuclei at the same level. Ultrastructurally, the free surface of the hindgut cells bears numerous microvilli and a few cilia. The lateral cell membranes are highly folded in the deflated hindgut, but these folds are not visible in the fully inflated hindgut. The cytoplasm contains osmiophilic bodies which show a partially lamellated pattern which may be sulfide oxidizing bodies involved in sulfide detoxification. In the fully inflated hindgut, the entire perimeter of the lumenal mucosa is covered by electron dense inclusions, whose exact fuction is unknown. The lack of structural information on the respiratory organ of this echiuran worm renders the interpretation of its morphological and histological features at the ultrastructural level difficult, although the present study has broadened our understanding of the structural adaptations of the hindgut as a respiratory organ. © 1992 Wiley-Liss, Inc.

Recognition of Fifth-Order Cycles in a Biodestratified Shelf Sandstone Parasequence: Olmos Sandstone, South Texas: ABSTRACT

This investigation of the Olmos Sandstone (Upper Cretaceous), A.W.P. field, McMullen County, Texas, demonstrates the utility of using genetic units and sequence stratigraphy to discern the depositional architecture of these enigmatic sand bodies. The Olmos represents a single parasequence within a transgressive systems tract. The parasequence is dated as Maastrichtian UC 15, based on planktonic foraminifera. A transgressive surface marked by submarine erosion caps the Olmos. The overlying glauconitic shale and marl is a regional marker horizon recognizable on seismic profiles and wireline logs and represents the rapid vertical deepening of facies. The Olmos is interpreted as a low-relief sand shoal that accumulated on the middle to outer shelf under low-energy conditions and slow rates of deposition. Internally, the Olmos parasequence is comprised of eight subtle cleaning-upward genetic subunits 10-20 ft thick which formed in response to incremental shallowing/deepening events associated with fifth-order sea level cycles. These in turn constitute the overall shoaling upward Olmos parasequence. Each subunit is comprised of lithofacies A (a relatively clean biodestratified reservoir-quality sandstone with a trace fossil assemblage of robust U-shaped and vertical burrows), lithofacies B (a shaly, biodestratified nonreservoir sandstone and siltstone with small, predominantly horizontal burrows); or a stacked A/B sequence. Subunitmore » contacts are gradational and burrowed; the upper contact is sharp and burrowed. The subunits correlate for 10 to 15 mi in both strike and dip directions except where shaled out or truncated by postdepositional erosion. These depositional concepts were used in conjunction with structure mapping and seismic inversion techniques to drill a successful outpost to A.W.P. field.« less

Burrow constructions during the development of Lumbricus badensis individuals

Juveniles of the anecic earthworm species Lumbricus badensis hatch from cocoon chambers, which the adult has excavated at depths between 0.4 and 1.5 m. After hatching the young animals migrate to the soil surface through the burrow of the adult. Juveniles live epigeically in self-constructed horizontal tubes during the first growing season. After hibernating in the soil at depths between 30 and 50 cm, juveniles make U-shaped burrows in the mineral soil. Later a main tube is constructed penetrating into the soil. This tube is split into two branches forming a V near the soil surface, and resembling the burrow of the adult. The burrow of an adult earthworm may reach a depth of 2.5 m and ramifies into 5–7 outlet tubes near the soil surface. The construction of the burrows during an individual's development, together with the transition from the epigeic to the anecic way of life, shows the close relationship of the anecic Lumbricus species to epigeic types. The feeding behaviour of the adult and the construction of the humic wall confirm this close relationship.

Feeding and digestion in Corophium volutator (Crustacea: Amphipoda)

New observations on the feeding behavior of Corophium volutator, collected from the Menai Strait, Anglesey, UK in 1981, show that detritus drawn into one entrance of the U-shaped burrow is pushed out at the opposing entrance either uningested or as faeces. Periodically, the amphipod turns around in the burrow and recommences feeding, so both the uningested material and the faeces may be reworked by the mouthparts. A feeding individual produces, on average, 16 faecal pellets every 10 min, at a seawater temperature of 18°C. When fed on detritus dyed with azo-carmine, approximately 12 pellets are produced before the foregut, intestine and hindgut are completely clear of previously ingested material and the dye appears in the faeces. Dye which enters the ventral caeca takes between 12 and 48 h to clear this tissue and, furthermore, it is only cleared when the amphipod is feeding. It is concluded that ingested coarse material is subjected only to a primary phase of digestion in the stomach, and that it takes 4 to 24 min to clear the gut. Fine material which enters the ventral caeca is subjected to a secondary phase of digestion and absorption which takes 24 to 48 h. Particles of thorium dioxide and ferritin incorporated in the diet are absorbed by the B- and ageing RF-cells in the ventral caeca. Non-specific esterases occur in the apical regions of the same cells, the mature cells of the anterior dorsal caeca and the cells at the anterior of the intestine. Protease activity is greatest in the lumen of the ventral caeca and the large vacuole of the B-cells. Apart from the lumen of the posterior caeca, there is some protease activity throughout the lumen of the gut. Carbohydrates were localised primarily in the R/F-cells towards the proximal region of the ventral caeca. Lipid was confined to the R/F-cells in the same region.

Quantitative methods in ichnology: spatial distribution among populations

Although patterns of dispersion are a fundamental attribute of modern populations, few attempts have been made to evaluate such spatial patterns in the rock record, evidently because of taphonomic uncertainties concerning in situ preservations of fossils. Unlike body fossils, however, ichnofossils almost inevitably remain in situ, and in some instances are indicative of contemporaneous populations of burrowers. Studies of dispersion among such ichnofossils, by means of the coefficient of dispersion and distance to nearest neighbour techniques, may reveal not only the spacing but also the specific trophic adaptations - and even the general identity - of the tracemakers. In this study, a population of the vertical shaft Skolithos linearis from the Lower Cambrian Bradorc Formation of Labrador exhibits an aggregated or clumped dispersal as a whole; yet individuals within the population exhibit random dispersion at low population densities and uniform dispersion at high population densities. These collective patterns, by analogy with modern tracemakers, suggest suspension feeders, either lophophorate phoronids or tentacular crowned polychaetes, as the ancient tracemaker. In contrast, a S. linearis population from the Middle Silurian Thorold Formation of Ontario exhibits random dispersion at all densities observed, suggesting that the ancient tracemaker was a polychaete that utilized either mucous nets or low, narrow tentacular crowns in suspension feeding. Populations of the vertical U-shaped burrow Diplocraterion sp., from the Thorold Formation, exhibit uniform to random dispersion, suggesting that it represents a dwelling burrow of a suspension-feeding polychaete. The uniform pattern resulted from a competition between individuals for living space. □Trace fossils, spatial distribution, Skolithos, Diplocraterion, trophic analysis. Palaeozoic.

Aspects of the biology of a gutless species of Solemya (Bivalvia: Protobranchia)

A new species of Solemya is found to lack a gut. It has no provision for the collection of food particles. The ciliation of the mantle cavity functions only to cleanse and irrigate the mantle cavity. Assay of glandular tissues and histochemistry reveal no digestive enzymological apparatus. It is inferred that this species obtains nutriment in the form of dissolved organic molecules. The ctenidia provide a large surface area for such a function, and the lamellae are well supplied with blood. This benthic species, which is most common in the vicinity of pulp mills, lives in a U-shaped burrow in soft mud. The burrow is lined with mucus which is secreted by the large pedal gland. The organism is capable of sustained swimming by repeated adduction of the valves, which causes jets of water to issue from the posterior exhalant opening.

Trace fossils from the Cambro-Ordovician cow head group, newfoundland, and their paleobathymetric implication

U-shaped burrows identified as the trace fossil Arenicolites occur in the Cambro-Ordovician Cow Head Group, a series of thin-bedded limestones interbedded with graptolitic shale and thick beds of limestone breccia and conglomerate. The lithology, limestone petrography, and trace fossils indicate deposition on a submarine slope of a slowly submerging carbonate platform. The limestone bed containing Arenicolites probably represents a period of slow deposition. The steeply inclined U-shaped burrows are assumed to have been formed by polychaete worms of the family Mochtyellidae which thrived in an argillaceous carbonate mud bottom of a carbonate platform slope, in depths exceeding 200 m. Although Arenicolites is believed to denote a shallow-water environment, its presence in the Cow Head extends the ecological niche of the Arenicolites-producing organisms into the outer shelf and continental slope. The domichnia of suspension feeders thus extends from shallow- to deep-water environments.

Biogenic Sedimentary Structures Produced by Crabs in Lagoon Margin and Salt Marsh Environments Near Beaufort, North Carolina

ABSTRACT Intertidal burrowing crabs produce distinctive biogenic sedimentary structures in protected lagoon margin and salt marsh environments in the vicinity of Beaufort, North Carolina. Distribution of crabs is determined primarily by substrate characteristics, salinity, and vegetation cover in the intertidal zone. Protected sand beaches and flats are heavily burrowed by the sand fiddler, Uca pugilator, which produces gently curved J-shaped and sharply curved L-shaped burrows 1 to 2 cm in diameter. Larger Y- and U-shaped burrows are formed by the ghost crab, Ocypode quadrata, in the backshore and foredune ridge zones above the high tide line. Salt marshes influenced by normal to near normal marine salinities are burrowed by U. pugilator, U. pugnax, and Sesarma reticulatum. U. pugnax and S. reticulatum burrow in muddy substrates, particularly along tidal creek banks, whereas U. pugilator is restricted to sandy substrate areas. U. pugnax burrows are 1 to 2 cm in diameter and have complex twisting and turning forms. The larger communal burrows of S. reticulatum consist of a complex of interconnected shafts with several oval-shaped surface openings. Panopeus herbstii is often found inhabiting these burrows. In salt marshes where the influence of fresh water is great, U. minax and U. pugnax are the dominant crabs. U. minax forms burrows 2 to 5 cm in diameter with ho ded entrances and long vertical shafts. Intertidal crabs are important agents of bioturbation in the environments that they inhabit. Their burrows have excellent potential for preservation in the sedimentary record. Recognition of the record of biogenic sedimentary structures produced by intertidal crabs would be of significant value in identifying paleoenvironments, fixing ancient lagoon margin and estuarine shorelines, and determining paleosalinities.

Muddy Sandstone Environments, Powder River Basin, Wyoming and Montana: Outcrop and Core Study: ABSTRACT

In the Powder River basin of Wyoming and Montana deltaic lobes have prograded from the east, northeast, and southwest at various times during the interval of time assigned to the Muddy Formation. Several recognizable sand-body types which yield hydrocarbons are associated with each of these deltas. The major types of reservoir sands are delta-distributary channels, barrier islands and high sand tidal-flat deposits. Each of these environments of deposition can be recognized in outcrop and in slabbed cores. After the environment is identified in a core, log shape is useful to extend the environment laterally. Examples from outcrops and cores from Wyoming and Montana illustrate the features which allow recognition of sands deposited in the various environments. In the barrier-island sands, such as those at Bell Creek field, low-angle crossbedding and a general coarsening upward from shale to silty sand to sandstone is present. Thalassinoides and a few Ophiomorpha burrows are locally present. In the tidal-flat sandstones wave and current ripples predominate. Long vertical burrows designated as Skolithos are prominent and brackish deposits such as coal are locally interbedded. Corophium, a small U-shaped burrow, is present in some of the cleaner intertidal sand bodies. Distributary-channel sandstones are typically medium to large scale trough crossbedded and locally have current ripples, climbing ripples, and interbedded clay drape in natural-levee deposits. Burrowing usually is limited to the upper part of the distributary-channel sands. Locally at the base of the channels is a conglomerate made up of clasts of marine shale. The uppermost part of the distributary-channel sands commonly are reworked and spread laterally as a thin transgressive beach or intertidal sand. A subregional paleogeographic reconstruction can be made utilizing the probable areal distribution and trends of each of the genetic sand limits. Maps of this type aid significantly in improving the success ratio of both exploration and development drilling. End_of_Article - Last_Page 918------------

Biogenic Sedimentary Structures in Facies of Middle Ordovician Black River Group of New York State: ABSTRACT

This study is based on analysis of 450 large vertical slabs from eight stratigraphic sections in the Black River Group type area, the Black River valley, northwest New York State. The group is underlain by an irregular Precambrian surface, is 90-140 ft thick, and consists of three formations: the basal Pamelia, the Lowville, and the Chaumont. These represent a sequence of six nearshore sedimentologic facies. Superimposed on these are four biogenic sedimentary structure facies, each characterized by particular biogenic structures. The Pamelia Formation consists of buff, algally laminated, fine-scale-mudcracked, supratidal dolomite characterized by rare vertical burrows like those of the succeeding Lowville Formation, and a sparse euryhaline fauna. The lower Lowville consists of lithologic types representing two environments: (1) gray, mudcracked, ripple-marked, thin-bedded, intertidal limestone with a euryhaline fauna, and (2) dark gray, thick-bedded, laminated, subtidal limestone containing algally coated grains and a sparse stenohaline fauna. The intertidal Lowville is characterized by permanent, vertical, and U-shaped burrows which today are most common in intertidal environments. Filter feeders usually construct these burrows for protection in environments characterized by stress at the interface. The subtidal part of the lower Lowville Formation is characterized by complex, irregularly oriented, feeding burrows, and large, concentrically laminated burrows. Today these types of burrows are common in quiet subtidal environme ts where deposit feeders dominate. The upper Lowville Formation represents a wave baffle formed by compound colonies of the spindle-shaped coral Tetradium associated with marginal zones of fallen Tetradium. These rocks are characterized by absence of biogenic structures, probably caused by the mechanical difficulty of burrowing into sediment with such a felted texture. The Chaumont Formation consists of silt-size debris of a diverse stenohaline biota, and is unbedded because of thorough burrowing. It is characterized by small, horizontal, sediment-filled burrows, which today dominate in level-bottom marine environments where a thin oxidized zone favors deposit feeders which cover broad horizontal areas near the sediment surface. Thus, integration of faunal, sedimentologic, and stratigraphic data with information on recent biogenic structures allows ecologic interpretation of Ordovician structures. End_of_Article - Last_Page 554------------

Substrate Selection by Corophium Species: The Particle Size of Substrates

Marine invertebrates which live in sand or mud are often limited to sediments or 'substrates' having a particular range of particle size (Pirrie, Bruce & Moore 1932; Thamdrup 1935; Yonge 1953; Steven 1953; Anon. 1957; Wieser 1959; Aldrich 1961). The amphipods Corophium arenarium Crawford and C. volutator (Pallas) are no exception to this rule: the former lives in sand and the latter in mud (Hart 1930; Thamdrup 1935; Crawford 1937; Beanland 1940; Watkin 1941; Holme 1949; Segerstrale 1959; Stock & de Vos 1960; Gee 1961; Anon. 1963). Both species inhabit permanent U-shaped burrows. The experiments reported below are concerned with why the two species are found in markedly different substrates. They form part of a series which were designed to elucidate the factors affecting substrate selection by C. arenarium and C. volutator (Meadows 1964a, b). Their subject is the influence of particle size. Other characteristics of the substrate which Corophium react to include substrate depth (Meadows 1964b), and the nature of naturally occurring films on substrate particles (Meadows 1964a).

FEEDING MECHANISM OF THE ECHIUROID, OCHETOSTOMA ERYTHROGRAMMON LEUCKART & RUEPPELL, 1828

1. Ochetostoma erythrogrammon built U-shaped burrows between mean low water neaps and mean low water springs in the intertidal sandy mud of Singapore and neighboring islands. 2. At ebb tide the proboscis emerged from the burrow in wet beaches to collect and swallow sand grains and detritus from the surface of the shore. 3. The ciliary currents on the proboscis and the course of the accepted and rejected particles were described. 4. The feeding mechanism of Ochetostoma erythrogrammon was compared with those of Echiurus echiurus and Urechis caupo.

The behaviour of polydora ciliata (Johnst.). Tube-building and burrowing

SUMMARYPolydora ciliata is a spionid polychaete found below mid-tidal level burrowing in a variety of rocks all of which contain calcium carbonate. It can also penetrate some non-calcareous materials such as rotten wood. It excavates a U-shaped burrow which it lines with a tube composed of mucoprotein and sand grains. This tube has a smooth inner lining of mucoprotein. Both food and tube-building material is collected by the palps and it is suggested that discrimination is made chiefly on size of the particle. Selection is made between the limits of 003-0-05 mm, the smaller particles passing down the gut whilst the larger are used in construction of the tube. A particle selection mechanism is suggested. The function of the segmental mucus glands is to provide the inner lining of the tube.The problem of chemical penetration of rocks by animals is discussed. P. ciliata uses both mechanical and chemical methods. No acid has been identified, and the use of a sequestering or chelating agent linked with the biochemistry of mucus is suggested.