Pallial Cavity Research Articles

UNCIHERPIA HIRSUTA A NEW GENUS AND SPECIES OF APLACOPHORAN (MOLLUSCA SOLENOGASTRES: PARARRHOPALIIDAE) FROM GALICIA, NORTHWEST SPAIN

During the sampling expeditions of the project FAUNA IBERICA, 14 specimens of a new species and genus of Solenogastres, Unciherpia hirsuta, were collected from the Banco de Galicia (NW Spain) (42°42′22″–42°43′00″; 11°47′52″W–11°45′47″W) found on Xthe coral Madrepora oculata (Linnaeus, 1758) at 760–769 m. depth. This new species is characterized by a body of 10.8 mm in length by 1.3 mm in width, without keel or lumps. Spicules are of four types: long, straight with a harpoon tip; acicular, slightly, curved with a serrated end; acicular and slightly sigmoid; and hooked with a sharp tip over the hook and the proximal end sigmoid-shaped. The mouth opening lies in the atrium; the ventral groove has one fold that does not enter the pallial cavity; there are 16 follicular glands encircling the pharynx and opening into it; there is a pair of short rostral caecum; one dorsoterminal sense organ; and eight respiratory folds. The creation of a new subfamily Unciherpiinae, of the family Pararrhopalidae is proposed to classify the new genera Unciherpia. This new sub-family is diagnosed by the hooked spicules and follicular glands around the pharynx.

The influence of classification on the evolutionary interpretation of structure a re-evaluation of the evolution of the pallial cavity of gastropod molluscs

Abstract The gastropod mantle, or pallial, cavity and its associated structures have served as a phylobase for studies of gastropod relationships for well over 100 years. We review C. M. Yonge's model for the evolution of the gastropod pallial cavity published a little more than 50 years ago, as well as its subsequent mutation by other authors. We then use a recently published (Ponder & Lindberg 1997) phylogenetic hypothesis of gastropod relationships to explore character transformations of attributes associated with the pallial cavity. Significant features of the evolution of the gastropod pallial cavity are the reduction or loss of structures (gill, osphradium, hypobranchial gland) and associated neural and reno-vascular systems on the right side of the cavity, and mechanisms for coping with an increase in overall body size in many clades. The loss of pallial cavity structures has occurred independently in several major clades, the patellogastropods, neritopsines, cocculinoideans, and apogastropods, and probably more than once in the vetigastropods. Evolution of the pallial cavity and associated structures is discussed for each of the clades in which largely different solutions are found to enable the achievement of larger body size. A seeming contradiction reduction of gills with increasing respiratory demand due to increasing body size is a feature of the group. We also examine possible linkages between the evolution of the pallial cavity and other morphological characters that were not suspect as a prioricorrelates of one another. The uncritical application of a current taxonomy to results obtained from applying the comparative method used to study form and function has been a significant hindrance to our understanding of evolution in the last several decades. C. M. Yonge's scenario published in 1947 was close to our phylogenetically based hypothesis. However, when it was later forced into agreement with the dominant classification of the last half-century (Thiele 1929–35), most of the points of agreement between the original scenario of Yonge and our phylogenetic hypothesis vanished, with four separate derivations reduced to a single event. This is an example of a Procrustean evolutionary scenario fitting the data to a classification scheme, with taxonomy rather than phylogeny used as the bed.

Feeding behaviour during brooding in the oyster Ostrea chilensis: gut retention time in adults and larvae and potential use of larval faeces by adults

The brooded larva of Ostrea chilensis is not an obligate lecithotroph, as has often been supposed, because it removes particles from the mantle cavity of the parent oyster. The ingestion of exogenous particles by the larva becomes apparent when the shell length of the veliger is approxi- mately 290 µm, the same stage at which the velar ciliature is also visible for the first time. Experi- ments using red plastic marker particles showed that gut retention time in brooding oysters was sig- nificantly greater (10 to 11 h) than in non-brooding oysters (8 h), providing a mechanism for more efficient use of the ingested food. Although there was no significant difference in gut retention time between oysters brooding early and late larval stages, the late brooders eliminated most of the faeces earlier than the early brooders. Experiments using 14 C-labelled algae demonstrated a shorter gut retention time in the larva (6 h) than in the non-brooding adult (10 h). Faeces from larvae contained relatively more chlorophyll a and less phaeopigment than faeces from brooding adults. The data sug- gest that the digestive system of the larva is much less efficient than that of the adult. Following the introduction of larvae previously fed 14 C-labelled algae into the pallial cavity of the brooding parent, the radiolabel was detected in the faeces of the adult, suggesting that the parent may ingest faeces produced by the larvae. The increase in gut retention time by the adult during the brooding period and the ingestion of larval faeces compensate for the high energy costs associated with the brooding process.

ONE SPECIES BECOMES TWO: THE CASE OF CHIONE CANCELLATA, THE RESURRECTED C. ELEVATA, AND A PHYLOGENETIC ANALYSIS OF CHIONE

The common € tropical α α β β western Atlantic venerid bivalve, Chione cancellata (Linnaeus), is revised on the basis of morphological, morphometric and phylogenetic analyses of conchological characters. Specimens inhabiting waters off the United States and Central America south to Belize comprise a separate species, described originally by Say as Chione elevata. The morphological and morphometric examination of numerous samples of both species supports the separation, pointing to differences of shell sculpture, hinge morphology and relative size of the pallial cavity. Morphological differences in sculpture suggest different functional characteristics of the species. A phylogenetic analysis of all extant species of Chione s.s. fails to resolve the relationship between C. cancellata and C. elevata. The parapatric separation of the two species reflects an ancient division of the tropical/sub-tropical western Atlantic into the northern Caloosahatchian Province and southern Atlantic Gatunian Province. This division dates back to at least the Early Pliocene. The fact that the differences between these two distinct species have been overlooked by systematists for almost 200 years suggests that we should re-examine western Atlantic species with broad geographic distributions similar to that of C. cancellata. It also suggests that we should pay closer attention to the taxonomy of common, ubiquitous species.

Particle transport in the zebra mussel, Dreissena polymorpha (Pallas).

The capture, transport, and sorting of particles by the gills and labial palps of the freshwater mussel Dreissena polymorpha were examined by endoscopy and video image analysis. More specifically, the morphology of the feeding organs in living zebra mussels was described; the mode and speeds of particle transport on the feeding organs was measured; and the sites of particle selection in the pallial cavity were identified. Particle velocities (outer demibranch lamellae, 90 microm s(-1); inner demibranch lamellae, 129 microm s(-1); marginal food groove of inner demibranchs, 156 microm s(-1); dorsal ciliated tracts, 152 microm s(-1)), as well as the movement of particles on the ctenidia and labial palps of D. polymorpha, are consistent with mucociliary, rather than hydrodynamic, transport. Particles can be sorted on the ctenidia of zebra mussels, resulting in a two-layer transport at the marginal food groove of the inner demibranch. That is: preferred particles are transported inside the marginal groove proper, whereas particles destined for rejection are carried superficially in a string of mucus. Sorting also occurs at the ventral margin of the outer demibranch; desirable particles are retained on the outer demibranch, whereas unacceptable particles are transferred to the inner demibranch and ultimately excluded from ingestion. We suggest that the structure of homorhabdic ctenidia does not preclude particle sorting, and that some ecosystem modifications attributed to zebra mussels may ultimately be due to ctenidial sorting mechanisms.

Functional anatomy of the respiratory system of Branchipolynoe species (Polychaeta, Polynoidae), commensal with Bathymodiolus species (Bivalvia, Mytilidae) from deep-sea hydrothermal vents

The gills of three species of Branchipolynoe have been studied in order to better understand the morphological and anatomical adaptations of their respiratory system. These Polynoidae live commensally inside the pallial cavity of different species of Bathymodiolus (Mytilidae), found clustered near deep-sea hydrothermal vents and cold seeps, and which harbor chemolithoautotrophic bacteria in their gills. As the mussels exploit hydrothermal fluid, the pallial cavity is perfused with a sulfide-rich hydrothermal water. The gills of Branchipolynoe species are well-developed branched outgrows of the body wall, located on the parapodia, and filled with coelomic fluid. They do not contain blood vessels. Living animals are red, due to the presence of extracellular hemoglobins in the coelom. The gill epidermis is made of supporting cells and a few ciliated cells arranged in longitudinal rows along the branches. Myoepithelial and ciliated cells line the interior of the coelomic cavity which contains the respiratory pigments. Coelomic fluid circulation inside the gills and body cavity is probably facilitated by both the cilia and myoepithelial contractions. The cuticle, the epidermis, and the coelomic epithelium are completely devoid of bacteria. The gill surface areas per unit body weight and the minimum diffusion distances, between external milieu and coelomic hemoglobins, have been calculated and compared with data already obtained on vascular gills of littoral or hydrothermal species of Polychaeta. In Branchipolynoe species, the respiratory surface area is very large, similar to that of a free-living hydrothermal species Alvinellapompejana, and the minimum diffusion distance is short, similar to that of the littoral species Arenicola marina. Although the organization of these coelomic gills in Branchipolynoe species is totally different from that of usual vascular gills, their characteristics represent a unique and effective respiratory system in Polynoidae which has adapted to the hypoxic and sulfide-rich micro-habitat which probably holds in the mantle cavity of vent mussels. In the gill epidermis, numerous secondary and large compound lysosomes are present which might be involved in sulfide detoxification.

Morphological study on Littorina Flava (King & Broderip) from Brazil (Caenogastropoda, Littorinidae)

A detailed morphological study of the littorinid Littorina flava (King & Broderip), from Venezuelan and Brazilian coasts, is given and commented. a considerable degree of shell characters variation was found, mainly in color and sculpture. The pallial cavity presents normal fashion of mesogastropods, without any detectable morphological modification for the long air-exposure. The digestive system present odontophore muscles very similar to those of the cerithioideans and hydrobioideans; the radula, however, is enormously long; the stomach lacks differentiate style sac. The penis is characteristic in lacking annex glands. The pallial oviduct has no jelly gland, and has a well developed bursa copulatrix and vaginal tube.

Dorymenia troncosoi sp. nov. (Mollusca Solenogastres: Proneomeniidae), a new species from the South Shetland Islands (Antarctica)

During the Spanish oceanographic expedition BENTART '95, carried out in Antarctic waters off Livingston Island (South Shetland Islands), five small specimens of a new species of Solenogastres-Cavibelonia, Dorymenia troncosoi sp. nov., were collected at a depth of 65–240 m on a silt bottom. The species is characterized by the presence of a pallial cavity with four pouches (a dorsal, two lateral and a ventral pouch), seminal receptacles that open into the spawning ducts through a short duct, radula having 9–11 teeth per row (1 central and 4–5 lateral, all the same size), the end of the copulatory spicules having a cross-section in the shape of a four-pointed star, and abdominal spicules present. These characteristics separate this species from other species of the genus, particularly from Dorymenia profunda, which is the most similar.

Particle sorting in bivalves: in vivo determination of the pallial organs of selection

Benthic particle feeders are exposed to a food supply varying in both quantity and quality. Previous studies have shown that bivalve molluscs deal with such fluctuating particle regimes in a variety of ways, including adjustments in pumping and ingestion rates, and selective rejection of non-nutritive particles as pseudofeces. The actual site of particle selection within the pallial cavity, however, has remained a topic of speculation. During August 1995 and January and August 1996, we exposed the oysters Crassostrea virginica (Gmelin) and C. gigas (Thunberg), and the mussel Mytilus trossulus Gould to a mixture of ground, aged Spartina alterniflora Loisel and similar-sized phytoplankton at three concentrations (103, 104, 105 particles ml−1). We then examined the ctenidia and labial palps by means of endoscopy and sampled, in vivo, the particulate material from various ciliated tracts, and analyzed the samples with a flow cytometer. We found that in oysters, the ctenidia are responsible for particle sorting, whereas the labial palps play an accessory role in particle selection, or function to control the volume of material to be ingested. In mussels, however, the ctenidia play little role in particle selection and simply transport particulate matter to the palps for further processing. We suggest that selection by the ctenidia of oysters is a function of their architecture (plicate, heterorhabdic).

Site of particle selection in a bivalve mollusc

Bivalve molluscs form dense populations that exert profound effects on the particle loads and phytoplankton composition of coastal waters1. It has long been known that bivalves can select among different particle types, including selecting against those of poor nutritional value2,3,4,5, but because of difficulties in observing particle transport processes in the pallial cavity in vivo, the mechanism of selection was not known. We now use a combination of video endoscopy6 and flow cytometry7 to show that oysters can select living particles from non-living detritus on the gills. Our methods could aid the study of suspension feeding in many animal groups.

Biodynamics of Suspension-Feeding in Adult Bivalve Molluscs: Particle Capture, Processing, and Fate

The technique of endoscopic examination and video-image analysis has allowed for in vivo observations of adult, bivalve molluscs and has led to a more accurate understanding of suspension-feeding processes in these animals. Several mechanisms, however, needed to be examined further. For example, the process by which particles are captured by the ctenidia remained unclear, and current models of this process did not adequately explain in vivo observations of capture events. In addition, the kinematics of particle processing by the labial palps and mode of particle ingestion have remained undefined. In this study I use results from endoscopic observations of nine species of bivalves to provide an integrated description of suspension feeding. These observations reveal that particle feeding is accomplished by both mucociliary and hydrodynamic mechanisms that often act simultaneously on the pallial organs. I introduce a model of particle capture that focuses on the ctenidial filament as the capture unit, unlike previous work that emphasized the laterofrontal cilia or cirri. The model is consistent with accepted fluid dynamic principles. In vivo observations in bivalves indicate that the suspension-feeding complex as a whole is, functionally, more than merely the sum of its parts. Additional key words: transport, ingestion, kinematics Suspension-feeding bivalves are a large group of ecologically and economically important aquatic animals. In many habitats they can be dominant infaunal or epibenthic organisms, affecting the surrounding community through processes such as benthic-pelagic coupling, particle depletion, and nutrient cycling (Peterson & Black 1987; Asmus & Asmus 1993; Smaal & Prins 1993). Therefore, many aspects of bivalve biology and ecology have been studied and described (Bayne et al. 1988; Bayne & Hawkins 1992; Bayne 1993; Dame 1993; Grant et al. 1993; Newell & Shumway 1993), including anatomical and physiological aspects of suspension-feeding (J0rgensen 1966, 1990; Owen 1974; Morton 1983). Most of these descriptions of suspension-feeding have been largely based on surgically altered specimens or on feeding structures isolated from the pallial cavity. While valid under certain circumstances, results from most of these studies should be interpreted with caution because surgery and isolation can: (1) cause feeding structures to function abnormally, (2) alter hydrodynamics of flow around the structures, and (3) destroy subtle interactions between adjacent feeding structures (e.g., ctenidia and labial palps). In addition, extrapolation of in vitro results to in vivo mechanisms implicitly assumes that the filaments or structures function as discrete units and that the feeding complex functions merely as the sum of its constituent parts (e.g., Nielsen et al. 1993). This may not be a valid assumption. In fact, previous researchers have suggested that mechanisms of feeding cannot be understood from studies on exposed ctenidia or ctenidial filaments (e.g., J0rgensen 1976). During the past several years, in vivo studies in intact bivalves by means of video endoscopy have provided a better understanding of suspension-feeding processes (Beninger et al. 1992; Ward et al. 1993; Ward et al. 1994). However, the details of many feeding processes, especially as they occur in intact animals, remain unclear. For example, the process by which particles are captured by the ctenidia has been a subject of debate for many years. Some workers have maintained that particles are mechanically trapped by rows of laterofrontal cilia or cirri (Tammes & Dral 1955; Dral 1967; Moore 1971), while others have suggested that particles are retained by hydrodynamic forces that operate at the level of interfilamentar spaces (Owen & McCrae 1976; J0rgensen 1981, 1990). AsThis content downloaded from 207.46.13.129 on Wed, 29 Jun 2016 04:33:02 UTC All use subject to http://about.jstor.org/terms Suspension-feeding biodynamics in bivalves pects of both theories, however, violate some of the physical and biological constraints imposed by the intact feeding system, and neither adequately explains in vivo observations of capture. The goal of this study was to integrate the observations and results obtained by video endoscopy, including previously unpublished data, with those obtained by more invasive techniques, in order describe a more holistic model of suspension-feeding biodynamics. Specifically, data on particle capture and transport by the ctenidia, transfer of particulate matter to the labial palps, processing of material by the palps, and ingestion of food material will be presented. I do not attempt a detailed, exhaustive explanation of feeding processes; rather, I focus on general mechanisms that are common to most suspension-feeding bivalves and that serve to unify this group. Where appropriate, my results are placed in the context of previous descriptions of feeding mechanisms in bivalves.

Association between the mollusc bivalve Loripes lucinalis and a Chlamydia-like organism, with comments on its pathogenic impact, life cycle and possible mode of transmission

Loripes lucinalis is a littoral bivalve which has already been confirmed to harbour endo-cellular sulfur-oxidizing bacteria within its gills. Examination of the digestive gland of L. lucinalis collected from the Moulin Blanc Beach in the Bay of Brest (Brittany, France) revealed the existence of an additional association involving a Chlamydia-like organism. Three different forms of Chlamydia-like bacteria were observed: reticulate rod-shaped cells, electron-dense cells and enlarged cells. The reticulate rod-shaped cells and the electron-dense bodies are thought to represent the germinal initial body and infectious form of the bacteria, respectively. The enlarged cells were always associated with what are believed to be spherical or icosahedral phages. Initial infestation seems to occur by phagocytosis at the apical pole of the digestive cells of the tubule and duct epithelia. Within the host cell, the bacteria undergo binary fission and budding, forming an inclusion which gradually fills up the cell. Inclusions are generally between 15 and 30 μm in size, and > 85% of all individuals examined possessed inclusion bodies. The level of infestation varied between individuals, some being heavily colonized, but did not seem to be related to season. Histological and ultrastructural observations suggest that, once developed, the colony has three possible fates: (1) the cells will degenerate due to phage infection; (2) colony overcrowding will occur, causing the development of electron-dense bodies that will be released into the lumen; (3) the entire membrane-bound inclusion will be released into the lumen and subsequently into the pallial cavity. Inclusions within the pallial cavity may be ingested by the host or may even be phagocytized by bacteriocyte cells of the gill. It is proposed that this association could be a form of symbiosis and that L. lucinalis may, therefore, be a rare example of an organism adapted to harbour two very different symbioses.

Feeding and digestive adaptations of bivalve molluscs to sulphide-rich habitats

Abstract From the standpoint of sulphide availability, marine bivalves are divided into three categories: Type 1, external environment and pallial cavities low in sulphides while submerged; Type 2, external environment containing sulphides but pallial cavity normoxic and low in sulphides due to irrigation via siphons; and Type 3, external habitat variably rich in sulphides and pallial cavity with some oxygen and also suphides, due to lack of siphons. This review presents the known anatomical and physiological adaptations associated with feeding and digestion in Type 3 bivalves, compared with Types 1 and 2. The principal anatomical adaptations of Type 3 bivalves to habitats of increasing sulphide availability are, in order of occurrence and degree: reduction of labial palps; reduction in length and volume of intestine; reduction in stomach volume; disappearance of crystalline style and style sac; reduction in digestive tubule volume; disappearance of digestive gland secretory cells; and total disappearance of the digestive system. In parallel with the above adaptations, an increasing physiological reliance on endosymbiotic bacteria is observed, as evidenced from δ 13C values. We conclude that, under similar conditions of environmental sulphide availability, similar adaptations are found in the feeding/digestive system, irrespective of taxon, depth or geographic location. The convergence between littoral and deep-sea vent and seep inhabitants is particularly striking.

Adaptations of the Aperture in Terrestrial Gastropod-Pulmonate Shells

In gastropod shells, the aperture is the most vulnerable part. Various structures evolved to minimize this local vulnerability. A systematic account of these structures is presented and discussed in an evolutionary context. In a marine environment, early in the evolution of the gastropods, the operculum is supposed to have originated as a door-like accessory to the shell aperture, protecting against predators. In amphibious species, it also functioned against desiccation. During the radiation of the pulmonate gastropods, the operculum got lost in most taxa. The pallial cavity, with a narrow pneumostome, evolved as a superior adaptation to terrestrial life. On land, a variety of aperture-obstructing structures, like, e.g., the clausilium, also evolved among pulmonates. It is hypothesized that this was triggered later on in geological time, by the origin of small predatory animals that initially were lacking. The operculum could not fulfil a function against predators anymore, because it had become obsolete already in these early pulmonates. The terrestrial prosobranch snails did not achieve an enclosed pallial cavity. Consequently, when they radiated on land, the operculum kept a vital function against desiccation and, later on, against predatory animals as well. This hypothetical scenario might explain the wealth of apertural structures in pulmonate shells, without an operculum, as compared to the relatively simple, roundish shell apertures of the always operculate terrestrial prosobranchs.

Occurrence of agglutinins in the pallial cavity mucus of oysters

Mucus and fluid from the pallial (mantle) cavity of eastern oysters Crassostrea virginica Gmelin from Chesapeake Bay and Galveston Bay were found to agglutinate a variety of vertebrate erythrocytes (RBC) and bacteria. Agglutinating activity of pallial cavity fluid was probably due to dissociation of agglutinins from mucus on the external surfaces of organs. Agglutination titers of pallial cavity fluid from individual Galveston Bay oysters for six different RBC were positively correlated with high significance, indicating a strong interdependence regardless of RBC specificity. The relative agglutinating activity for different RBC by tissue explants and homogenized tissues (mantle, gill, digestive gland and adductor muscle) was similar to the relative activity of the pallial cavity fluid; mantle and gill tissue had the greatest agglutinating capacity over all RBC, whereas the adductor muscle had the least. Positive correlation was detected between agglutination titers of pallial cavity fluid (for different RBC) and titers of hemolymph agglutinins from the same oysters. It is hypothesized that agglutinins in the pallial cavity and hemolymph have a common source. The results of the explant and homogenate assays can be interpreted to suggest that the source is mantle and gill tissues.

The anatomy of some new archaeogastropod limpets (Order Patellogastropoda, Suborder Lepetopsina) from hydrothermal vents

The anatomy of one species of neolepetopsid limpet, Eulepetopsis vitrea (Order Patellogastropoda, Suborder Lepetopsina), is described, and this is followed by comments on differences shown by four other members of the Suborder, Neolepetopsis occulta, N. densata, N. gordensis and Paralepetopsis fioridensis.These limpets possess features linking them directly with limpets from other habitats, in this case with patellogastropods. Shared external features relate to the shallow pallial cavity with no gill; the single fold of the mantle edge, which is sensory, glandular, and has a respiratory function; in the gut the presence of inner as well as outer lips, with a strongly arched dorsal jaw associated with the former; the absence of an epipodium; and the cavity of the protoconch sealed from that of the teleoconch by a septum. The relationship displayed by internal anatomy is even more striking: the docoglossate radula and licker; the oesophageal glands forming a series of pouches, each with its own opening to the oesophagus; the stomach a simple ciliated sac lacking gastric shield, sorting area, and caecum; the enlarged initial part of the intestine; the orientation of the chambers of the heart, which is not traversed by the rectum; the lack of haemocyanin; the opening of the gonad directly to the base of the papilla of the right kidney; the absence of secondary sexual structures; the small left kidney displaying characters of a nephridial gland; and the degree of concentration of the main ganglia and the arrangement of the visceral loop. This aggregate of characters shows that the neolepetopsids cannot be separated from patellogastropods.The radula of the neolepetopsid differs from that of other patellogastropods in its unmineralized and articulating teeth and in the presence of a rachidian: the first feature appears to be a derived character and the other two ancestral. These radular differences contrast with the anatomical homogeneity exhibited not only here but throughout the patellogastropods. Such anatomical differences as do occur are most easily explained as mosaic evolution.

Pumping Rates, Water Pressures, and Oxygen Use in Eight Species of Marine Bivalve Molluscs from British Columbia

Pumping characteristics and oxygen utilization for Solemya reidi, Yoldia thraciaeformis, Chlamys hastata, Mytilus edulis, Crassostrea gigas, Clinocardium nuttallii, Saxidomus giganteus, and Mya truncata were studied. Pressures were recorded using a Yale A79 spinal tap needle inserted in the pallial cavity or siphonal aperture. Pumping volumes were determined through particulate analysis using a Model B Coulter counter and oxygen consumption by standard Winkler titration modified for small samples. The species chosen were selected to represent progressive increases in gill complexity and siphon length. The minimum pressure differential across the gill (20 Pa) was observed for Y. thraciaeformis while the maximum pressure gradient (600 Pa) was recorded for M. truncata. Pumping rates varied from 1.41 L∙h−1∙g−1 (Y. thraciaeformis) to 4.71 L∙h−1∙g−1 (C. hastata) and species with siphons tended to pump at lower rates. The deeply burrowing M. truncata consumed 3.5 times as much oxygen (0.63 mL O2∙h−1∙g−1) as S. reidi (0.18 mL O2∙h−1∙g−1) which inhabits anoxic environments. For all species, the metabolic cost of pumping was less than 1% of the total oxygen uptake.

Glacidorbidae (Glacidorbacea: Basommatophora), a new family and superfamily of operculate freshwater gastropods

Some aspects of the anatomy of Glacidorbis hedleyi Iredale are described and its systematic position is reviewed. Glacidorbis is a genus of operculate gastropods found in Australia and South America, the species of which possess a monoseriate or triseriate radula and brood their embryos in the pallial cavity. Glacidorbis hedleyi is a protandrous hermaphrodite with, sometimes, 50% or more of large individuals remaining as males. The reproductive system is diaulic, with the penis being lost in mature females. It feeds on the tissue of freshly killed or wounded animals and has a very simple alimentary canal. A new family and superfamily is created for Glacidorbis within the Basommatophora. A new subgenus, Gondwanorbis, is introduced for Glacidorbis magallanicus Meier-Brook & Smith from Chile, S America.

Comportement exp�rimental de Lingula anatina (Brachiopoda: Inarticulata) dans divers substrats meubles (Baie de Mutsu, Japon)

Lingula anatina Lamarck was collected from the vicinity of Asamushi, Japan, in May 1982. Burrowing up to the surface by this brachiopod compensates for natural sedimentation above its burrows and is essential to its survival. Its speed of ascent was measured during experiments using various soft substrates in aquaria (coarse >2 mm and fine 2 mm in situ sediment). In all experiments, L. anatina was able to move up through the sediment, but ascent speed differed between the substrates. Ascent through the in situ sediment was much faster, since the sediment layer was deeper (up to 30 cm), and was achieved without autotomy of its pedicle which can attain a length 20 times greater that of its shell. Ascent is also rapid in brachiopods without pedicles,but such individuals maintain their filtering position with difficulty and generally emerge onto the sediment surface. In coarse-grained substrate (>2 mm) lacking fine-grained particles, L. anatina moves up but is unable to construct a burrow, and finally emerges onto the sediment surface, often after complete autotomy of its pedicle. In very fine sediment (<50 μm), L. anatina is able to burrow without clogging its pallial cavity with the very fine particles, but its valves are inadequately supported by the soft burrow walls in such fluid sediment, and maintenance of its filtering position is not possible. Our results invalidate some general concepts about suspension-feeders. The role of the pedicle is limited to anchorage at the bottom of the burrow and to retraction into the burrow; in certain cases it appears to be a handicap to ascent to the sediment surface.

The histology and histochemistry of the pedal glandular system of two limpets,Patella vulgataandAcmaea tessulata(Gastropoda: Prosobranchia)

Patella vulgatapossesses nine different pedal glands, six of which pour their secretions on to the sole. Proteins secreted by the marginal gland into the marginal groove are used for locomotion, especially when the limpet moves off following a period of adhesion. Another protein-secreting subepithelial gland, sparsely present throughout the foot, is also believed to be used in locomotion. A third gland type is present in the epithelium of the sole. The secretion of these epithelial mucocytes which is a weakly acidic muco-polysaccharide (MPS) is likely to have a locomotory function. Three other sole glands secrete highly viscous acidic MPS. Their secretions are likely to have an adhesive function. The three other glands present in the foot are contained within the side-wall. Of these, two are believed to secrete mucus to protect the animal against desiccation during emersion; and the other, present only in youngP. vulgata, pours its acidic MPS secretion into the epipodial streak. This secretion consolidates debris before it is cleared from the pallial cavity; in adult animals, muscular contractions of the foot are powerful enough to clear debris without the help of the epipodial gland.InAcmaea tessulatathe six glands present open out on to the sole and correspond in position, composition and function to the six glands of the sole ofP. vulgata. There are no glands within the side-wall.