Interrelationships between developing oocytes and ovarian tissues in the chiton Sypharochiton septentriones (Ashby) (Mollusca, Polyplacophora).
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Acid Phosphatase↗
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Oocyte-follicle cell differentiation in two species of amphineurans (Mollusca), Mopalia mucosa and Chaetopleura apiculata.
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Animals↗
The cephalic sensory organ in veliger larvae of pulmonates (Gastropoda: Mollusca).
The apical area of larvae of four primitive pulmonate species was investigated by means of serial ultrathin and light microscope sections. Cephalic sensory organs (CSOs) were found in the larvae of Onchidium cf. branchiferum (Onchidiidae) and Laemodonta octanfracta (Ellobiidae), while no trace of the organ was present in the larvae of Ovatella myosotis (Ellobiidae) or Williamia radiata (Siphonariidae). TEM investigation revealed very similar CSOs in O. cf. branchiferum and L. octanfracta, with characteristic putative sensory cell types: ampullary cells with an internal ampulla containing densely packed cilia, para-ampullary cells with external cilia parallel to the surface, and ciliary tuft cells, bearing short ciliary tufts. The epithelium covering the organ has a thick microvillar border with microvilli laterally bearing a pair of electron-dense accumulations and a glycocalyx with interspersed flat plaque-like elements. While homologues of all major elements of the CSO can be found in other gastropod taxa, for example caenogastropods and opisthobranchs, the homology of the ampullary cell with similar cells in nongastropods appears unlikely. The CSO of L. octanfracta is associated with an additional structure, an epithelial external protrusion, lying ventral to the CSO. The absence of the organ in W. radiata weakens hypotheses on the organ's function of examining settlement conditions and velar control.
Animals↗
Fine structure and immunocytochemistry of a new chemosensory system in the Chiton larva (Mollusca: Polyplacophora).
Combined electron microscopy and immunocytochemistry of the larvae of several polyplacophoran species (Chiton olivaceus, Lepidochitona aff. corrugata, Mopalia muscosa) revealed a sensory system new to science, a so-called "ampullary system." The cells of the "ampullary system" are arranged in four symmetrically situated pairs lying dorsolaterally and ventrolaterally in the pretrochal part of the trochophore-like larva and they send axons into the cerebral commissure. They are lost at metamorphosis. The fine structure of these cells strongly resembles that of so-called "ampullary cells" known from various sensory organs of other molluscs, such as the apical complex of gastropod and bivalve larvae, osphradia of vetigastropods, and olfactory organs of cephalopods, and nuchal organs of certain polychaetes. The ampullary cells and their nerves are densely stained by anti-FMRF-amide fluorescence dyes, whereas antiserotonin staining is only weak. While cytological homology of the ampullary cells with those of other organs is probable, the ampullary system as a whole is regarded as a synapomorphy of the Polyplacophora or Chitonida.
Animals↗
Ultrastructure of the sperm and spermatogenesis in five South African species of the trochid genus Oxystele (Mollusca, Prosobranchia).
Sperm of Oxystele are of the primitive type, which is typical of molluscs using external fertilization. They comprise a head, which is composed of a barrel-shaped nucleus and large conical acrosome; a midpiece of five or six spherical mitochondria; and a tail, with a 9 + 2 arrangement of microtubules. The morphology of the sperm broadly resembles that of the sperm of other trochids as well as that of the sperm of the Pleurotomariidae, Haliotidae, and Fissurellidae but differs considerably from that of the Patellidae. Each of the five species examined was found to have a different sperm morphology. Our results support the suggestion of Heller and Dempster (in preparation) that Oxystele variegata Anton actually consists of two sympatric species. The morphological changes that occur during spermatogenesis are very similar in all species and resemble descriptions given for other molluscs with primitive sperm.
Animals↗
Chromatin condensation and acrosome development during spermiogenesis of Ensis ensis (Mollusca, Bivalvia).
We describe chromatin condensation and acrosome development during spermiogenesis of Ensis ensis. The overall shape of the mature spermatozoon corresponds to the primitive type. The nucleus is oval and on its superior pole there is an elongated acrosome; the middle piece contains four mitochondria around the centriolar complex. The condensation of the nuclei seems to occur in three steps: first the diameter of chromatin fibers increases slightly from 17 to 20 nm; second, in midspermatids fiber pairs coalesce; and third, the coalescence continues by addition of other fibers until the nuclei become highly compacted. Chromatin changes are related with nuclear protein composition. Small proacrosomal vesicles show two regions of different electron density. At a later stage they fuse to give a single, spherical vesicle in round spermatids, which migrates to the upper pole and transforms into a tapered acrosome (18 microns long) with a central channel filled with finely fibrous material.
Acrosome↗
Ultrastructural and cytochemical study of spermatogenesis in Scrobicularia plana (Mollusca, Bivalvia).
The ultrastructure of the mature spermatozoa and spermatogenesis of the bivalve Scrobicularia plana are described. Support cells extend from the basal lamina to the lumen of the testis and are laterally connected to the germinal epithelium. Germ cells present intercellular bridges and flagella since the spermatogonial stage. While spermatogonia and spermatocytes appear connected to support cells by desmosome-like junctions, elongated spermatids are held at the acrosomal region by support cell finger-like processes. During spermiogenesis, the acrosomal vesicle differentiates from a golgian saccule and then migrates to the nuclear apex. A microtubular manchette arising from centrioles surrounds the acrosomal vesicle, the nucleus, and the mitochondria at the time these three organelles start their elongation, disappearing after that. The mature spermatozoon of S. plana lacks a distinct midpiece because the mitochondria extend from the region of the pericentriolar complex along the nucleus anteriorly for approximately 1.4 microns. The features of this bivalve type of modified spermatozoon are compared with those of other animal groups having similar modifications.
Acid Phosphatase↗
Molecular cloning and expression analysis of vitellogenin in scallop, Patinopecten yessoensis (Bivalvia, Mollusca).
The present study was undertaken to determine scallop vitellogenin (Vtg) cDNA sequence, to identify Vtg synthesizing cell, and to analyze the regulation of Vtg mRNA expression. Clones containing partial cDNA sequence of Vtg were isolated from cDNA library of the scallop ovary by immunoscreening with the anti-scallop vitellin (Vn) serum. The deduced amino acid sequence of the clone containing the longest cDNA insert (1,689 bp) was identified as a member of the lipid transport protein family and exhibited about 20-35% identity with Vtgs of other oviparous animals. Northern blot analysis identified a single transcript longer than 10 kb in the ovary. Dot blot analysis of the ovary showed a high amount of Vtg mRNA during the growing stage and the level was retained until spawning stage. In situ hybridization demonstrated the expression of Vtg mRNA in the auxiliary cells closely associated with growing oocytes, suggesting that the synthesis of a major yolk protein in the scallop occurs through hetero-synthetic pathway without mediation through the blood flow but occurs de novo in the ovary. The content of Vtg mRNA in the ovarian tissue cultured in vitro with vitellogenesis promoting factor (VPF), which strongly promotes Vtg protein synthesis, from the cerebral plus pedal ganglion (CPG) showed no change. The transcription of Vtg mRNA appeared to be promoted by estradiol-17beta (E2) not by VPF although VPF may enhance the translation of Vtg mRNA.
Amino Acid Sequence↗
Cell lineage of the prototroch of Patella vulgata (Gastropoda, Mollusca).
The trochophore larva of the archaeogastropod mollusc Patella vulgata has a well-developed locomotory organ, the ciliated prototroch. This structure is formed from specific founder cells, the trochoblasts. Two methods were employed to determine the composition and cell lineage of the prototroch. Fluorescent cell-lineage tracer injection in trochoblasts and trochoblast founder cells was used to show how the various trochoblasts became incorporated into the prototroch. Scanning electron microscopy was used to study both differentiation, more specifically ciliation, of trochoblasts and localization of trochoblasts in the prototroch. The results obtained with both methods are in accordance with each other. During early development all trochoblasts involved in prototroch formation become cell cycle-arrested and develop cilia. Subsequently, the trochoblasts shift in position to form a circular prototroch and a number of trochoblasts deciliate. As a result of these processes the mature prototroch consists of a number of heavily ciliated cells as well as a number of deciliated cells. Comparison of prototrochs from a number of spiralian species shows that this structure is very conserved during evolution. The significance of this is discussed.
Animals↗
Cleavage pattern and mesentoblast formation in Acanthochiton crinitus (Polyplacophora, Mollusca).
In characteristic spiralian embryos the mesentoblast is the stem cell of the mesodermal bands. It is a derivative of the dorsal quadrant. At least in gastropod molluscs, the ancestral form for the specification of the dorsal quadrant out of four initially equal quadrants is by centralization of one of the four macromeres after the separation of the presumptive ecto- and entoblast cells. Then this macromere is induced by the animal micromeres to produce the mesentoblast. In this paper it is shown that in the embryo of the polyplacophoran Acanthochiton crinitus, specification of the dorsal quadrant and formation of the mesentoblast exactly follow the same pattern. After deletion of the first quartet of micromeres none of the macromeres is centralized, no mesentoblast is formed, and the embryo remains radially symmetrical. Apparently, the mechanism for the specification of the dorsal quadrant and the formation of the mesentoblast has been conserved during the evolution of the main molluscan taxa. It has been discussed whether this mechanism might be a plesiomorphous property, characteristic of less derived spiralian phyla.
Animals↗
Occurrence of Contracaecum sp. larvae (nematoda, anisakidae) in Gundlachia radiata (Guilding, 1828) (mollusca, gastropoda, ancylidae) in Brazil.
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Animals↗
Comparison of the soluble organic matrices of healthy and diseased shells of Pinctada margaritifera (L.) and Pecten maximus L. (Mollusca, Bivalvia).
Pinctada margaritifera and Pecten maximus are among the mollusks of commercial value. Both are known to show abnormal calcification processes that strongly increase the mortality rate. Several parameters of the soluble organic matrices extracted from the shells of P. margaritifera and P. maximus are analyzed: bulk composition, molecular weights, and acidity. The composition of the matrices of healthy and diseased shells were compared, showing that the protein and the sugar contents are variously modified. Differences between healthy and diseased shells are dissimilar in the two species. This is in accordance with the previously described macroscopic and microscopic alterations (red color, numerous brown membranes). This study does not allow identification the origin of the disease, but provides new insights on the role of sugars in biomineralization processes.
Acids↗
New clades of euthyneuran gastropods (Mollusca) from 28S rRNA sequences.
Recent morphological and molecular results on phylogeny of euthyneuran gastropods, which include opisthobranchs and pulmonates, have greatly diminished previous supposed resolution of their phylogenetic relationships. In addition to recent morphological results, sequences of the D1 and D2 domains of the 28S rRNA are here analyzed by parsimony for 31 euthyneuran species. The molecular and previous morphological data sets were not congruent according to an ILD test, and morphological and molecular data could not be analyzed simultaneously. Consequently Bremer's Combinable Component Consensus was used to obtain a new tree, with the following supported molecular results: monophyly of a new clade of opisthobranchs including actively swimming Euthyneura, i.e., pelagic Gymnosomata and Thecosomata plus benthic Anaspidea; first molecular confirmation of monophylies of Hygrophila, including Chilina, Acteonoidea, and Sacoglossa, which include both shell-bearing species and slugs; and new confirmation of the monophyly of Stylommatophora. Morphological characters which support the new clades obtained here are discussed.
Animals↗
A molecular phylogeny of the Octopoda (Mollusca: Cephalopoda) evaluated in light of morphological evidence.
In this paper we examine the phylogenetic relationships of the Octopoda utilizing molecular sequence data from the cytochrome c oxidase subunit I (COI) gene and compare results from analyses of molecular data with classifications and phylogenies based on previous morphological studies. Partial COI sequences (657 bp, excluding primers) were obtained from 28 species representing most of the diversity in the Order Octopoda, along with a sequence from the established sister taxon to the Octopoda, Vampyroteuthis infernalis. Our results exhibit a number of basic differences from inferences based on standard morphological data. We attempt to resolve these differences based on our confidence in various morphological features. An important finding is the failure of the molecular data to support the monophyly of the Octopodidae. This family contains over 90% of the species in the Suborder Incirrata and has always been difficult to define. Statistical tests constraining Octopodidae monophyly by use of parsimony and maximum-likelihood techniques suggest that all incirrates may be derived from octopodids.
Animals↗
Molecular phylogeny of a circum-global, diverse gastropod superfamily (Cerithioidea: Mollusca: Caenogastropoda): pushing the deepest phylogenetic limits of mitochondrial LSU rDNA sequences.
The Cerithioidea is a very diverse group of gastropods with ca. 14 extant families and more than 200 genera occupying, and often dominating, marine, estuarine, and freshwater habitats. While the composition of Cerithioidea is now better understood due to recent anatomical and ultrastructural studies, the phylogenetic relationships among families remain chaotic. Morphology-based studies have provided conflicting views of relationships among families. We generated a phylogeny of cerithioideans based on mitochondrial large subunit rRNA and flanking tRNA gene sequences (total aligned data set 1873 bp). Nucleotide evidence and the presence of a unique pair of tRNA genes (i.e., threonine + glycine) between valine-mtLSU and the mtSSU rRNA gene support conclusions based on ultrastructural data that Vermetidae and Campanilidae are not Cerithioidea, certain anatomical similarities being due to convergent evolution. The molecular phylogeny shows support for the monophyly of the marine families Cerithiidae [corrected], Turritellidae, Batillariidae, Potamididae, and Scaliolidae as currently recognized. The phylogenetic data reveal that freshwater taxa evolved on three separate occasions; however, all three recognized freshwater families (Pleuroceridae, Melanopsidae, and Thiaridae) are polyphyletic. Mitochondrial rDNA sequences provide valuable data for testing the monophyly of cerithioidean [corrected] families and relationships within families, but fail to provide strong evidence for resolving relationships among families. It appears that the deepest phylogenetic limits for resolving caenogastropod relationships is less than about 245--241 mya, based on estimates of divergence derived from the fossil record.
Animals↗
Sediment analysis does not provide a good measure of heavy metal bioavailability to Cerastoderma glaucum (Mollusca: Bivalvia) in confined coastal ecosystems.
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Animals↗
Unusual aggregations of tubules associated with endoplasmic reticulum in digestive cells of Alderia modesta (Mollusca: Gastropoda: Sacoglossa).
Aggregations of cylindriform tubules closely packed in a hexagonal arrangement and associated with the rough-surfaced endoplasmic reticulum (RER) are described in cells of the digestive gland of a sacoglossan gastropod. Each tubule is approximately 61 nm in outer diameter and the central lumen is lined with a layer of finely granular material. The tubule wall is composed of approximately 22 dense subunits. Adjacent tubules are associated with a pair of indistinct granules. Membranes of the RER frequently join the aggregations. The lumen of a tubule may be continuous either with the intracisternal space of the RER or with the cytoplasmic matrix of the cell. It is suggested that the aggregations of tubules are elaborations of the endoplasmic reticulum.
Animals↗
The fine structure of epidermal lines on arms and head of postembryonic Sepia officinalis and Loligo vulgaris (Mollusca, Cephalopoda).
The structure and cell types of the epidermal lines that are found on the surface of the head and arms of Sepia officinalis and Loligo vulgaris, were investigated by light- and transmission electron microscopy. The lines consist of ciliated cells and non-ciliated, accessory cells. The axon of the ciliated cell and the ultrastructure of the latter indicate that this element is sensory; therefore, the epidermal lines of cephalopods may be regarded as a type of sensory organ.
Animals↗