Mantle Lobe Research Articles

Comparative larval myogenesis and adult myoanatomy of the rhynchonelliform (articulate) brachiopods Argyrotheca cordata, A. cistellula, and Terebratalia transversa

BackgroundDespite significant methodological progress, Brachiopoda remains one of the lophotrochozoan phyla for which no recent ontogenetic data employing modern methodologies such as fluorescence labelling and confocal microscopy are available. This is particularly astonishing given the ongoing controversy concerning its phylogenetic position. In order to contribute new morphogenetic data for phylogenetic and evolutionary inferences, we describe herein the ontogeny and myoanatomy of larvae and adults of the rhynchonelliform brachiopods Argyrotheca cordata, A. cistellula, and Terebratalia transversa using fluorescence F-actin labelling combined with confocal laserscanning microscopy.ResultsFully grown larvae of A. cordata and T. transversa consist of three distinct body regions, namely an apical lobe, a mantle lobe with four bundles of setae, and a pedicle lobe. Myogenesis is very similar in these two species. The first anlagen of the musculature develop in the pedicle lobe, followed by setae muscles and the mantle lobe musculature. Late-stage larvae show a network of strong pedicle muscles, central mantle muscles, longitudinal muscles running from the mantle to the pedicle lobe, setae pouch muscles, setae muscles, a U-shaped muscle, serial mantle muscles, and apical longitudinal as well as apical transversal muscles. Fully developed A. cistellula larvae differ from the former species in that they have only two visible body lobes and lack setae. Nevertheless, we found corresponding muscle systems to all muscles present in the former two species, except for the musculature associated with the setae, in larvae of A. cistellula. With our survey of the adult myoanatomy of A. cordata and A. cistellula and the juvenile muscular architecture of T. transversa we confirm the presence of adductors, diductors, dorsal and ventral pedicle adjustors, mantle margin muscles, a distinct musculature of the intestine, and striated muscle fibres in the tentacles for all three species.ConclusionOur data indicate that larvae of rhynchonelliform brachiopods share a common muscular bodyplan and are thus derived from a common ancestral larval type. Comparison of the muscular phenotype of rhynchonelliform larvae to that of the other two lophophorate phyla, Phoronida and Ectoprocta, does not indicate homology of individual larval muscles. This may be due to an early evolutionary split of the ontogenetic pathways of Brachiopoda, Phoronida, and Ectoprocta that gave rise to the morphological diversity of these phyla.

Diet–tissue isotopic fractionation of the Pacific oyster Crassostrea gigas

Juveniles of the Pacific oyster Crassostrea gigas were reared on a monospecific micro- algal diet in order to quantify their 13 C and 15 N diet-tissue fractionations. The weights of these juve- niles increased by up to 18-fold within 33 d. The juveniles reached isotopic equilibria with the diet, enabling calculations of fractionation values. The 13 C fractionation for tissues containing lipids ranked as 0.6‰ (gill lamella) >0.3‰ (adductor muscle) > -0.2‰ (mantle lobe) > -0.9‰ (whole soft body) > -2.2‰ (midgut gland), while the 15 N fractionation ranked as 8.7‰ (adductor muscle) >6.5‰ (mantle lobe) >5.4‰ (whole soft body) >5.2‰ (gill lamella) >2.3‰ (midgut gland). Removal of lipids shifted the diet-equilibrated δ 13 C and δ 15 N values in all tissues except the adductor muscle, with resultant increases in the 13 C and 15 N fractionation values. The expected annual mean δ 13 C value for the diet of the oyster in the field is -17.0‰, which is an intermediate value among the δ 13 C of coastal phytoplankton (-20.2‰), epilithon (-20.0‰), epipelon (-14.8‰), and seaweeds (-14.9‰), suggesting that the oyster feeds on a mixture of these micro- and macroalgae. The expected δ 15 N diet value is 3.1‰, which is more depleted than values for micro- and macroalgae, suggesting that the 15 N fractionation in the field is smaller than that obtained from the feeding experiment.

Structure of the brachiopod lophophore

Data on the development, structure, and functional morphology of the brachiopod lophophore are analyzed. The common origin of the tentacle apparatus in Lophophorata from the postoral ciliary band of the larva is shown. The brachiopod lophophore is based on the brachial axis consisting of the brachial fold running along the row of tentacles. The brachial axis may be attached to the brachial (dorsal) mantle lobe (trocholophe, schizolophe, and ptycholophe lophophores) or extend freely into the mantle cavity to form coiling brachia (spirolophe, zygolophe, and plectolophe lophophores). The circulation of water flows through the mantle cavity in the brachiopods with attached and free lophophores is described. A new hypothesis on the sorting of particles suspended in water during filtration is proposed.

TEM immunocytochemistry of a 48 kDa MW organic matrix phosphoprotein produced in the mantle epithelial cells of the Eastern oyster ( Crassostrea virginica)

Immunohistochemical TEM of Eastern oyster ( Crassostrea virginica) mantle epithelial cells using a polyclonal antibody to a gel purified 48 kDa MW oyster shell phosphoprotein revealed that it is phosphorylated in the Golgi, packaged into secretory vesicles and subsequently exocytosed across the apical membrane of specialized cells. These phosphoprotein producing cells are concentrated along the mantle side facing the shell, in the region of the outer mantle lobe. A layer of calcium enriched immuno-reactive mucous is associated with the apical microvilli of these cells. The 48 kDa phosphoprotein forms a component of the fibrous organic matrix and appears to be involved in calcium supply thus enabling crystal growth at the mineralization front.

Out of Australia: Belloliva (Neogastropoda: Olividae) in the Coral Sea and New Caledonia

The genus Belloliva (Gastropoda: Olividae) consists of small (<15 mm) operculate species and was hitherto thought to be essentially confined to coastal waters of southern and eastern Australia. We report a small radiation from deep water (100–1000 m) in the Coral Sea and New Caledonia, consisting essentially of undescribed species. The new genus Calyptoliva, which differs from Belloliva by the absence of a mantle filament and the presence of a mantle lobe, is also represented in the same area by new species. Based on correlation with shell characters, we suggest that the olivid mantle lobe is responsible for secreting the primary spire callus that overlies the suture, rather than producing the columellar callus as was previously believed (Marcus and Marcus 1959). Belloliva and Calyptoliva combine a suite of shell, radular, and anatomical characters that is shared with either the Olivinae or the Ancillariinae. This raises the question of the distinctiveness of the two classically recognized subfamilies within the family Olividae. All species have paucispiral protoconchs with inferred limited larval dispersal, and many have extremely narrow distributions, sometimes endemic to a single guyot, or they show discrete geographical differentiation. New species: Belloliva iota sp. nov., Belloliva alaos sp. nov., Belloliva apoma sp. nov., Belloliva ellenae sp. nov., Belloliva obeon sp. nov., Belloliva dorcas sp. nov., Calyptoliva bolis gen. nov., sp. nov., Calyptoliva amblys sp. nov., Calyptoliva tatyanae sp. nov.

Earliest ontogeny of Middle Ordovician rhynchonelliform brachiopods (Clitambonitoidea and Polytoechioidea): implications for brachiopod phylogeny

New data on the earliest ontogeny of Mid-Ordovician Baltoscandian clitambonitoid (Apomatella, Neumania and Oslogonites) and polytoechioid (Antigonambonites and Raunites) brachiopods reveal significant differences in the life history of the taxa belonging to these two superfamilies. The Polytoechioidea and probably other members of the Billingsellida had planktotrophic larvae, in which the dorsal and ventral mantle lobes formed separately and without reversion. The ‘pedicle sheath’ in Antigonambonites is secreted by a section of modified ventral mantle and thus this ‘pedicle’ is not homologous within the pedicle of rhynchonellate brachiopods. It is likely that polytoechioids and other members of the strophomenate clade had the same type of ontogeny and mode of attachment. In contrast, the ontogeny and mode of attachment of clitambonitoids are similar to that of recent rhynchonellates: their mantle lobes and both valves formed simultaneously, and the pedicle most likely formed from the larval pedicle lobe. Evidence for the lecithotrophic nature of clitambonitoid larva is discussed. This confirms that the Clitambonitoidea, unlike the Polytoechioidea, represents an ingroup within the Rhynchonellata.

Variation in ^|^delta;13C and ^|^delta;15N among different tissues of three estuarine bivalves: implications for dietary reconstructions

The stable isotope approach to dietary reconstructions is based on the consistent isotopic fractionation between diet and consumer. Despite the rapidly increasing use of stable isotopes in studies on bivalves, classical fractionation values (0–1‰ for δ13C and 3–4‰ for δ15N) are used in the literature irrespective of the tissue analyzed and of the sample preparation method. We measured δ13C and δ15N for lipid-removed and lipid-containing tissues (adductor muscle, foot, mantle lobe, siphon, labial palp, gill lamella, midgut gland, and male and female gonad) of three suspension feeding bivalves (Crassostrea gigas, Cyclina sinensis and Ruditapes philippinarum) to provide an essential calibration for the diet-tissue fractionation. There were similar tissue-specific patterns in the δ13C and δ15N, which rank adductor muscle>other tissues>midgut gland or female gonad. Removal of lipids raised the δ13C and δ15N for all tissues of the three species. Acid treatment of the total soft tissues of R. philippinarum had no significant effects on the isotopic compositions. Diet-tissue fractionations for R. philippinarum were estimated based on the known fractionation values for the lipid-containing total soft tissues. Lipid removal and associated rinsing raised not only the 13C fractionation by 0.4–1.5‰ but also the 15N fractionation by 0–0.8‰, resulting in large fractionation values outside of the range of currently accepted 13C and 15N fractionation. The present study demonstrates that isotopic analyses are affected by the choice of tissue type and sample preparation method.

The transition from planktotrophy to lecithotrophy in larvae of Lower Palaeozoic Rhynchonelliform brachiopods

Criteria are established for defining the presence of protegula formed on embryonic or larval mantle in representative genera of Lower Palaeozoic Obolellata, Strophomenata and Rhynchonellata. Width was used to define protegular type. Taxa with only an embryonic protegulum are inferred to have had lecithotrophic larvae while taxa with a larval protegulum or an embryonic protegulum surrounded by a larval protegulum are inferred to have had planktotrophic larvae. All or most of the taxa examined in the Obolellata, the Strophomenata and the orders Protorothida and Orthida in the Rhynchonellata had planktotrophic larvae. In the Pentamerida a minority of genera had only a larval, or an embryonic and a larval protegulum while a majority had protegular widths indicating lecithotrophy. In the orders Rhynchonellida, Atrypida, Athyrida and Spiriferida derived from the Pentamerida (with the exception of one species in the Atrypida) a number of the genera had protegular widths indicating lecithotrophy. It is suggested that the onset of lecithotrophy in the Pentamerida was associated with a developmental innovation in which the mantle lobe of the larva was reflected over the apical lobe during the process of metamorphosis. This evolutionary innovation probably occurred during the late Cambrian or early Ordovician and was subsequently inherited during the process of cladogenesis.

A revision of some Asian and African freshwater clams assigned to Type="Italic"&gt;Corbicula fluminalis (M�ller, 1774) (Mollusca: Bivalvia: Corbiculidae), with a review of anatomical characters and reproductive features based on museum collections

A study of museum specimens of the genus Corbicula from the western Asiatic part of its range (Middle East, the Caucasus and Central Asia) has provided the following diagnostic anatomical characters for Corbicula fluminalis (Muller, 1774): siphons narrow with circular apertures; siphonal papillae rather scarce: about 40 around inhalant siphon (one or two rows) and 12--20 around exhalant siphon (one incomplete row); ring of dark pigment usually present internally at base of each siphon; papillae of fused mantle lobes and free mantle edge numerous, the first organised in one or two rows; radial muscles of mantle edge well developed and arranged in bands. Presence of hermaphroditic specimens, biflagellate type of spermatozoa indicating clonality, and incubation of D-shaped 190--217 μm long larvae in gills were also shown for this taxon. Two conchologically different morphotypes referred to in literature as C. fluminalis s. str. and C. purpurea (Prime, 1864) show also slight differences in size of spermatozoa and may represent different clonal lineages. The lots from North Africa possess the same characters as one of the Asian morphotypes, thus taxonomic distinctness of C. fluminalis consobrina (Cailliaud, 1827) is not supported. In contrast, C. africana (Krauss, 1848) distributed in Lake Malawi and South Africa and treated in some modern reviews as another subspecies of C. fluminalis differs by the patterns of shell sculpture, the lower number of siphonal papillae, the absence of pigmentation on the siphons and their papillae, and the size of spermatozoa; its distinctness is therefore supported, but close affinity to C. fluminalis needs confirmation. All studied African morphotypes are identical in their mode of reproduction. The new data on the anatomy and reproduction of C. fluminalis show strong similarities between this taxon and the ‘eastern’ incubating species C. fluminea (Muller, 1774), but these taxa can be distinguished by their shell characters. The Chinese estuarine non-incubating Corbicula earlier assigned to C. fluminalis shows different anatomical and reproductive characters and is re-considered as C.cf. japonica (Prime, 1864). These results are discussed in the framework of Corbicula phylogeny based on molecular characters.

THE RELATIONSHIP BETWEEN THE UNILATERAL SIPHONAL ORGAN AND LABIAL PALPS OF MACOMA CONSTRICTA (BRUGUIÈRE, 1792) (BIVALVIA: TELLINIDAE)

Macoma constricta has unequal siphons, the inhalant being longer and larger. Living animals were collected from muddy sand where they laid on the left valve with the long axis of the shell more or less horizontal. In dissected individuals, sand grains and detritus were identified in the ventral pallial channel and the digestive tract, indicating a normal habit of deposit feeding. Where the inflow of water occurs, a siphonal organ is present on the left mantle lobe. The labial palps are well developed and capable of considerable contraction and extension. Four thin plicae occur on the subterminal tip of the left inner labial palp and show slow undulatory movements. Palp plicae are localized near the thin distal wall of the unilateral siphonal organ. Studies of the anatomies of the labial palp and siphonal organ identified ciliary currents on the latter. The functions of the few palp plicae and siphonal organ are associated with the monitoring of water quality incursing the mantle cavity. The siphonal organ may also assist the palps in re-sorting particles in the mantle cavity.

A new approach to pearl oyster broodstock selection: can saibo donors be used as future broodstock?

Cultured pearl production requires grafting of a pearl nucleus, together with a piece of mantle tissue (‘saibo’) from a donor oyster, into a recipient oyster. The donor mantle tissue is an important factor in determining pearl quality. It is desirable that donor oysters resulting in high quality pearls be used as the basis for future hatchery production to ensure high quality pearl production; however, donor oysters are killed as part of the grafting process. This study was conducted to assess the feasibility of keeping donor pearl oysters alive as potential broodstock. To determine whether mantle tissue could be removed from oysters without mortality, Akoya pearl oysters ( Pinctada fucata) were anaesthetised with 500 mg l −1 of benzocaine and had the ventral margin of either their left, right or both left and right mantle lobes removed. Survival after 4 weeks was 100% for all treatments and oysters showed regeneration of excised mantle tissue. After 3 months, histological analyses showed complete regeneration of the mantle and its structures. These findings show that donor pearl oysters recover from removal of mantle tissue and could be used as future broodstock for pearl culture operations.

Regional specification during embryogenesis in Rhynchonelliform brachiopods

Fate maps have been constructed for embryos of Hemithiris and Terebratulina, representatives of two orders in the class Rhynchonellata that have been separated since the middle Ordovician. These fate maps are identical. The animal region of the egg forms the ectodermal covering of the apical lobe and the vegetal region is the site of gastrulation; the vegetal region forms the ectoderm of the ventral and posterior regions of the larva, endoderm and mesoderm. The cells that make up the animal region shift 90° with respect to the vegetal pole during gastrulation. The timing and mode of regional specification in these two species are also identical. In each case, the animal region of the unfertilized egg has the intrinsic ability to form apical lobe ectoderm, while the vegetal region has the ability to form a normal larva. During embryogenesis, the vegetal region interacts with the animal region to suppress apical tuft differentiation in the apical lobe and to promote mantle lobe ectodermal differentiation, while the ability of the vegetal half to regulate by forming apical lobe structures is lost. The plane of bilateral symmetry of the larva begins to be set up between the late blastula and early gastrula stage. The fate maps and the processes of regional specification are compared in the four subphyla that make up the Brachiopoda and used to test a developmental model that provides an explanation for the variety of different body plans generated during the Cambrian.

The Nature of Siliceous Mosaics Forming the First Shell of the Brachiopod Discinisca

The juvenile shell of the brachiopod Discinisca consists of a mosaic of micrometer-sized siliceous tablets embedded in a chitinous substrate. The first-formed tablets are secreted on glycocalyx by a newly differentiated collective of outer epithelial cells. They are mainly rhombic but may also be ellipsoidal, discoidal, or deformed and sporadically overlap one another. On the surrounding juvenile shell, secreted by an incipient outer mantle lobe, the tablets are nearly all perfect rhombic plates in rhombic arrays. Their constant size, arrangement, and centripetal crystallization suggest intracellular assembly. The tablets, which are normally bilamellar, consist of discrete aggregates of crystalline spherules of silica in rhombic arrays within an organic matrix of fibrous protein and, presumably, a soluble polysaccharide(s). Mosaic secretion ceases at about the time when juveniles settle on the sea bed, which more or less coincides with the secretion of a ring of lamellae around the mosaic, induced by rapid advances and retractions of the outer mantle lobe prior to deposition of the organophosphatic mature shell. Energy dispersion X-ray analyses of pelagic and newly settled juveniles show that phosphatic secretion, even in the site of the first-formed outer epithelial collective, does not begin until all siliceous secretion has ceased.

Regional Specification during Embryogenesis in the Craniiform Brachiopod Crania anomala

A fate map has been constructed for the embryo of Crania. The animal half of the egg forms the ectodermal epithelium of the larva's apical lobe. The vegetal half of the egg forms endoderm, mesoderm, and the ectoderm of the mantle lobe. The vegetal pole is the site of gastrulation; this site becomes the posterior ventral region of the mantle lobe of the larva. The plane of the first cleavage goes through the animal–vegetal axis of the egg; it bears no relationship to the future plane of bilateral symmetry of the larva. The timing of regional specification was examined by isolating animal, vegetal, or meridional halves from oocytes, eggs, or embryos from prior to germinal vesicle breakdown through gastrulation. Animal halves isolated from oocytes formed either the epithelium of the apical lobe or a larva with all three germ layers. Animal halves isolated from unfertilized eggs and eight-cell embryos formed only apical lobe epithelium. Beginning at the blastula stage, animal halves formed mantle in addition to apical lobe epithelium. In animal halves isolated after gastrulation, the mantle lobe was always truncated. Vegetal halves isolated at all stages prior to gastrulation gastrulated and formed apical and mantle lobes with endoderm and mesoderm; however, the relative size of the apical lobe that formed decreased substantially when vegetal halves were isolated at later developmental stages. When meridional halves were isolated from unfertilized eggs and two- to four-cell embryos, both halves frequently formed normally proportioned larvae. Beginning at the blastula stage, a number of pairs frequently had a member that lacked dorsal setae on its mantle lobe while the other member of the pair formed setae, indicating that the dorsoventral axis had been set up. The process of regional specification in Crania is compared to those of Discinisca and Glottidia in the brachiopod subphylum Linguliformea and Phoronis in the phylum Phoronida.

Reproductive cycles and larval morphology of three Recent species of Argyrotheca (Terebratellacea: Brachiopoda) from Mediterranean submarine caves

Although the three examined species of Argyrotheca are quite common in the Mediterranean, little is known about their reproductive cycles. This study shows that Argyrotheca cordata and Argyrotheca cistellula have continuous breeding activity, indicated by the occurrence of ripe eggs and larvae in their brood pouches throughout the year. The absolute number of larvae found in the brood pouches of both species corresponds to the adult's size. The third species examined, Argyrotheca cuneata, tends to breed in autumn, with larvae only present in September and November, but the sample-size was small. Larval development is very similar in all three Argyrotheca species, each embryo going through a gastrula stage, a two-lobed and a three-lobed stage. Before leaving the brood pouch, the larvae have an apical lobe with a girdle of elongated cilia, a mantle lobe with a midventral band of cilia and a pedicle lobe without ciliation. The larvae of A. cordata and A. cuneata possess four bundles of larval setae, whereas A. cistellula shows no setae at all.

Regional Specification during Embryogenesis in the Inarticulate BrachiopodDiscinisca

The process of embryogenesis is described for the inarticulate brachiopodDiscinisca strigataof the family Discinidae. A fate map has been constructed for the early embryo. The animal half of the egg forms the dorsal ectoderm of the apical and mantle lobes. The vegetal half forms mesoderm and endoderm and is the site of gastrulation; it also forms the ectoderm of the ventral regions of the apical and mantle lobes of the larva. The plane of the first cleavage goes through the animal–vegetal axis of the egg along the future plane of bilateral symmetry of the larva. The timing of regional specification in these embryos was examined by isolating animal, vegetal, or lateral regions at different times from the 2-cell stage through gastrulation. Animal halves isolated at the 8-cell and blastula stages formed an epithelial vesicle and did not gastrulate. When these halves were isolated from blastulae they formed the cell types typical of apical and mantle lobes. Vegetal halves isolated at all stages gastrulated and formed a more or less normal larva; the only defect these larvae had was the lack of an apical tuft, which normally forms from cells at the animal pole of the embryo. When lateral isolates were created at all developmental stages, these halves gastrulated. Cuts which separated presumptive anterior and posterior regions generated isolates at the 4-cell and blastula stages that formed essentially normal larvae; however, at the midgastrula stage these halves formed primarily anterior or posterior structures indicating that regional specification had taken place along the anterior–posterior axis. The plane of the first cleavage, which predicts the plane of bilateral symmetry, can be shifted by either changing the cleavage pattern that generates the bilateral 16-cell blastomere configuration or by isolating embryo halves prior to, or during, the 16-cell stage. These results indicate that while the plane of the first cleavage predicts the axis of bilateral symmetry, the axis is not established until the fourth cleavage. The development ofDisciniscais compared to development in the inarticulate brachiopodGlottidiaof the family Lingulidae and toPhoronisin the phylum Phoronida.

Invasive orchitophryid ciliate infections in juvenile Pacific and Kumomoto oysters, Crassostrea gigas and Crassostrea sikamea

During an extensive survey of juvenile oyster health from shellfish nursery facilities in Washington state, USA, a primary invasive ciliate disease was discovered. Ciliates invaded the extrapallial space and coelomic cavity of juvenile Pacific and Kumomoto oysters ( Crassostrea gigas and Crassostrea sikamea) which had a shell height of from 0.5 mm to 2.0 mm. Both diploid and triploid oysters were affected but no infections were found in oysters larger than 3.0 mm shell height. The invasion was initiated when ciliates were able to bypass the outer mantle lobe and gain entry to the extrapallial space. Subsequently, the thin mantle tissue separating the extrapallial space from the coelomic cavity was breached. Once the extrapallial space was invaded in these small shellfish seed, the infection appeared to be irreversible. Cumulative mortality in affected cultures usually exceeded 50%, and the infection was considered a serious although sporadically occurring problem for nursery production of early stage seed. The ciliates were ovoid with a tapered anterior end and round in cross section with an estimated maximum body width averaging 18 μm and body length averaging 32 μm. The ciliates were holotrichously ciliated with a modal number of somatic kineties for these samples of 13. The cytoplasm of the ciliates was typically full of food vacuoles, which appeared to contain debris and in several cases what appeared to be entire nucleated cells. The invasive ciliates have an obvious anterior oral cavity and cytostome with at least two oral polykinetids and a paroral. Based on the shape of the oral cavity, they belong in the Order Scuticociliatida and can be most easily placed in the Family Orchitophryidae. In contrast to a previous report describing ciliates in oyster seed cultures, this infection was considered primary but opportunistic. Strategies for preventing and managing the infection are discussed.

The biology and functional morphology of Minnivola pyxidatus (Bivalvia: Pectinoidea)

The shallow subtidal scallop Minnivola pyxidutus occurs in the relatively clean oceanic, southern, and south‐eastern waters of Hong Kong and elsewhere in the Western Pacific and is highly polymorphic in terms of shell patterning of the left, upper valve. Locally, because of sea‐bed perturbations, numbers are declining. The species can probably live for ∼ 3 years, with reproduction occurring in winter. M. pyxidatus is monoecious.Shell form and anatomy are described. Normally, the species lives attached by a fragile byssus to sand grains or stones, but can swim, albeit weakly, in response to predation risks.In most respects, Minnivola pyxidatus is a typical scallop, with a bowl‐shaped, right lower valve and a concave, disc‐like, left upper valve. The mantle has pallial eyes and a complex array of tentacles which possess small, ciliary‐based sensory cells. There is also a cleansing tract on the outer surface of the middle mantle fold and a muscular velum formed from the inner fold. The latter is developed into a simple exhalant aperture posteriorly. Both mantle lobes possess extensive posterior pallial glands and an abdominal sense organ on the right lobe only, anterior to the single posterior adductor muscle. Ciliary currents of the mantle cavity are for cleansing and are powerful, particularly on the visceral mass and right mantle lobe but not the left.The ctenidia and their ciliary currents are typical of the Pectinidae except that the ascending lamellae of all demibranchs are greatly reduced and, it is suggested, previse the situation seen in the Propeamussiidae where they are lost and the ventral margins of the inner and outer descending lamellae fuse to create an ‘inside out’ gill. Unusually, the labial palps of Minnivola pyxidatus are fused to the mantle and visceral mass, preventing their collapse in the mantle cavity and thus maintaining particle selection efficiency. The gut is simple. Left and right statocysts are unusually equal and the pericardium is located dorsal to the adductor muscle. Minnivola pyxidatus is adapted to an epibenthic life on subtidal sands and muds. Powerful cleansing currents and an ability to swim have allowed this species to survive in dredged and trawled waters with high levels of settling and resuspended silt.

Scanning electron microscopy, whole-mount histology, and histochemistry of two anodontine glochidia (Bivalvia: Unionidae)

Intramarsupial glochidia of Anodonta anatina (L.) and Pseudanodonta complanata (Rossmässler) were studied in southern Finland. Material staining positively with periodic acid – Schiff's reagent (PAS), neutral lipid reserves, and acid phosphatase activity have different distributions in the mantle of the two species. Moreover, the mucous covering of the mantle of the two glochidia behaves differently on critical-point drying. The presence of microvilli with alkaline phosphatase activity on the mantle surface and acid phosphatase activity in the mantle cells in both glochidia suggest that the mantle plays a role in nutrient uptake and digestion and possibly also in electrolyte uptake. The primordia of the stomach, digestive diverticula, and intestine, at least in A. anatina glochidia, contain neutral lipids and exhibit acid phosphatase activity: In A. anatina glochidia, a microvillous layer with alkaline phosphatase activity continues from the ventral walls of the lateral pits to the suspected kidney diverticula. In both glochidia, there may be three pairs of rudimentary ganglia, which do not stain with methylene blue. The eight ciliated sense organs of the glochidia are methylene blue- and PAS-positive and they exhibit succinate dehydrogenase and acid phosphatase activity. In each mantle lobe, the enveloping cell of the dorsal ciliary organ is interconnected with those of the ventral triad via a cellular fold or "tract," and the ciliated central cells of the organs send axons towards each other.

Differential accumulation and depuration of human enteric viruses by mussels

The tissue distribution of adenovirus 40 (ADV) and human rotavirus, serotype 3 (HRV) was determined after feeding the common mussel (Mytilus spp.) with high levels of clay-associated virus. At different time intervals, individual tissues were carefully dissected and assayed for infectivity. Viruses were detected in contaminated mussels after 1-hour contact, and maximum levels were observed after 6 hours. Most infectious viruses were located in the gills and in the digestive tract. Decreasing virus numbers were found in the mantle lobes. Mussels contaminated with poliovirus 1 (PV), hepatitis A virus, strain HM-175 (HAV), ADV, HRV, and bacteriophages of Bacteroides fragilis (B40-8) were depurated in 50-1 tanks with a continuous flow of ozonated marine water. After 96 hours, HAV and HRV suffered less than 2 Log10 titre reduction (LTR), while ADV showed a 2.7 LTR. PV showed a 3 LTR after 48 hours and became undetectable thereafter. Bacteriophage B40-8 suffered less than 2 LTR after 96 hours, suggesting that it could be an appropriate indicator of the efficiency of virus elimination during shellfish depuration.