Fouling deterrence on the bivalve shell Mytilus galloprovincialis: a physical phenomenon?

The physical nature of fouling deterrence by the mussel Mytilus galloprovincialis was investigated using high-resolution biomimics of the bivalve surface. The homogeneous microtextured surface of M. galloprovincialis (1.94 +/- 0.03 microm), the smooth surface of the bivalve Amusium balloti (0 microm), and moulds of these surfaces (biomimics) were compared with controls of smooth (0 microm) and sanded moulds, (55.4 +/- 2.7 microm) and PVC strips (0 microm) in a 12-week field trial. The shell and mould of M. galloprovincialis were fouled by significantly fewer species and had significantly less total fouling cover than the shell and mould of A. balloti over a 12-week period. However, the major effects were between surfaces with and without microtopography. Surface microtopography, be it structured as in the case of M. galloprovincialis shell and mould, or random as in the case of the sanded mould, had a lower cover of fouling organisms than treatments without microtopography after 6 weeks. There was also no difference between the effect of the M. galloprovincialis mould and the sanded mould. The strong fouling deterrent effects of both these surfaces diminished rapidly after 6 to 8 weeks while that of M. galloprovincialis shell remained intact for the duration of the experiment suggesting factors in addition to surface microtopography contribute to fouling deterrence.

Articulated Palaeozoic fossil with 17 plates greatly expands disparity of early chitons

Modern chitons (Mollusca: Polyplacophora) possess a highly conserved skeleton of eight shell plates (valves) surrounded by spicules or scales, and fossil evidence suggests that the chiton skeleton has changed little since the first appearance of the class in the Late Cambrian period (about 500 million years before present, Myr bp). However, the Palaeozoic problematic taxon Multiplacophora, in spite of having a more complex skeleton, shares several derived characters with chitons. The enigmatic status of the Multiplacophora is due in part to the fact that its members had an exoskeleton of numerous calcium carbonate valves that usually separated after death. A new articulated specimen from the Carboniferous period (about 335 Myr bp) of Indiana reveals that multiplacophorans had a dorsal protective surface composed of head and tail valves, left and right columns of overlapping valves (five on each side), and a central zone of five smaller valves, all surrounded by an annulus of large spines. Here we describe and name the articulated specimen and present evidence that multiplacophorans were chitons. Thus the highly conserved body plan of living chitons belies the broad disparity of this clade during the Palaeozoic era.

Conch shell structure and its effect on mechanical behaviors

The shell of pink conch is a kind of natural well-designed composite with excellent mechanical properties, which provides us information for material design. In this paper the microstructures of pink conch shell are characterized by using SEM and TEM. The microscopic analysis indicates that the pink conch shell is with crossed-lamellar microstructure and the angle between two second-order lamellae is 70-90 degrees. The cracking and fracture morphologies indicate that the crack deflection, bridge and fiber pullout are the main toughening mechanisms. Bamboo lamellae are employed to make the simple bio-mimetic model materials. In the model material the rotated angle between the fibers of each glued lamella varies from 0 degrees to 90 degrees. Three-point-bending is employed to test the properties of models material, such as the elastic modulus, the flexural strength and the fracture strain energy density. It is found that the fracture strain energy density of the specimens with the rotated angle between the fibers of the layers about 60 degrees exhibits the maximum value, which is close to the angle of the two second-order lamellae of the conch shell.

Light production by the arm tips of the deep-sea cephalopod Vampyroteuthis infernalis

The archaic, deep-sea cephalopod Vampyroteuthis infernalis occurs in dark, oxygen-poor waters below 600 m off Monterey Bay, California. Living specimens, collected gently with a remotely operated vehicle (ROV) and quickly transported to a laboratory ashore, have revealed two hitherto undescribed means of bioluminescent expression for the species. In the first, light is produced by a new type of organ located at the tips of all eight arms. In the second, a viscous fluid containing microscopic luminous particles is released from the arm tips to form a glowing cloud around the animal. Both modes of light production are apparently linked to anti-predation strategies. Use of the tip-lights is readily educed by contact stimuli, while fluid expulsion has a much higher triggering threshold. Coelenterazine and luciferase are the chemical precursors of light production. This paper presents observations on the structure and operation of the arm-tip light organs, the character of the luminous cloud, and how the light they produce is incorporated into behavioral patterns.

Original molluscan radula: comparisons among Aplacophora, Polyplacophora, Gastropoda, and the Cambrian fossil Wiwaxia corrugata

As the original molluscan radula is not known from direct observation, we consider what the form of the original radula may have been from evidence provided by neomenioid Aplacophora (Solenogastres), Gastropoda, Polyplacophora, and the Cambrian fossil Wiwaxia corrugata (Matthews). Conclusions are based on direct observation of radula morphology and its accessory structures (salivary gland ducts, radular sac, anteroventral radular pocket) in 25 species and 16 genera of Aplacophora; radula morphogenesis in Aplacophora; earliest tooth formation in Gastropoda (14 species among Prosobranchia, Opisthobranchia, and Pulmonata); earliest tooth formation in four species of Polyplacophora; and the morphology of the feeding apparatus in W. corrugata. The existence of a true radula membrane and of membranoblasts and odontoblasts in neomenioids indicates that morphogenesis of the aplacophoran radula is homologous to that in other radulate Mollusca. We conclude from p redness of salivary gland ducts, a divided radular sac, and a pair of anteroventral pockets that the plesiomorphic state in neomenioids is bipartite, formed of denticulate bars that are distichous (two teeth per row) on a partially divided or fused radula membrane with the largest denticles lateral, as occurs in the genus Helicoradomenia. The tooth morphology in Helicoradomenia is similar to the feeding apparatus in W. corrugata. We show that distichy also occurs during early development in several species of gastropods and polyplacophorans. Through the rejection of the null hypothesis that the earliest radula was unipartite and had no radula membrane, we conclude that the original molluscan radula was similar to the radula found in Helicoradomena species.

[RNA polymerase II and pre-mRNA splicing factors in diplotene oocyte nuclei of the giant African gastropod Achatina fulica]

The nuclear distribution of pre-mRNA splicing factors (snRNPs and SR-protein SC35) and unphosphorylated from of RNA polymerase II (Pol II) was studied using fluorescent and immunoelectron cytochemistry in diplotene oocytes of the gastropod Achatina fulica. Association of Pol II and splicing factors with oocyte nuclear structures was analysed. The antibodies against splicing factors and Pol II were shown to label perichromatin fibrils at the periphery of condensed chromatin blocks as well as those in interchromatin regions of nucleoplasm. The revealed character of distribution of snRNPs, SC35 protein, and Pol II, together with the decondensed chromatin and absence of karyosphere, enable us to suggest that oocyte chromosomes maintain their transcriptional activity at the diplotene stage of oogenesis. In A. fulica oocytes, sparse nuclear bodies (NBs) of a complex morphological structure were revealed. These NBs contain snRNPs rather than SC35 protein. NBs are associated with a fibrogranular material (FGM), which contains SC35 protein. No snRNPs were revealed in this material. Homology of A. fulica oocyte nuclear structures to Cajal bodies and interchromatin granule clusters is discussed.

An ultrastructural study of connective tissue in mollusc integument III. Cephalopoda

We studied structure and ultrastructure of the subepidermal connective tissue (SEC) of the integument of three cephalopods (Sepia officinalis, Octopus vulgaris and Loligo pealii). In all species, three distinct regions of the SEC were recognised: (a) an outer zone (OZ) that included the dermal-epidermal junction, and consisted of a thin layer of connective tissue containing muscles, (b) an extensive middle zone (MZ) containing a compact network of collagen fibres and numerous cells, (c) an inner zone (IZ) of loose connective tissue that merged with muscular fascia. This arrangement differs from that in bivalves and gastropods and recalls vertebrate integument. The dermal-epidermal junction of cephalopods differed from that of bivalves, gastropods and mammals in that the epidermal cells did not possess hemidesmosomes, and their intermediate filaments terminated directly in the plasmamembrane. The thick (120-500 nm) basal membrane (BM) had a superficial zone containing a regular array of granules; a lamina densa composed of a compact network of small filaments and granules; and an IZ distinguished by expansions of granular material protruding into underlying structures. Collagen fibres contained fibroblast-derived cytoplasmic thread, running through their centres and were surrounded by granular material that joins them to adjacent fibres. The collagen fibrils were of medium diameter (30-80 nm) had the typical ultrastructure of fibrillar collagens, and were surrounded by abundant interfibrillar material. The hypodermis was loose, with a network of small bundles of collagen fibrils. Cephalopod integument appears to represent a major evolutionary step distinguishing this class of molluscs.

Soluble organic matrices of the calcitic prismatic shell layers of two Pteriomorphid bivalves. Pinna nobilis and Pinctada margaritifera

The calcitic prisms of the shells of two bivalves, Pinna and Pinctada, are considered simple prisms according to some morphological and mineralogical characteristics. Scanning electron microscopic and atomic force microscopic studies show that the microstructures and nanostructures of these two shells are different. Pinna prisms are monocrystalline, whereas Pinctada prisms are not. Moreover, intraprismatic membranes are present only in the Pinctada prisms. The soluble organic matrices extracted from these prisms are acidic, but their bulk compositions differ. Ultraviolet and infrared spectrometries, fluorescence, high pressure liquid chromatography, and electrophoresis show that the sugar-protein ratios and the molecular weights are different. Sulfur is mainly associated with acidic sulfated sugars, not with amino acids, and the role of acidic sulfated sugars is still underestimated. Thus, the simple prism concept is not a relevant model for the biomineralization processes in the calcitic prismatic layer of mollusk shells.

Structural organization of the nervous system of the mantle cavity wall and organs in prosobranch mollusks

A variety of common histological stains was used, along with the Golgi and Colognier silver impregnation methods and electron microscopy, to perform a comparative study of the morphological characteristics of receptor and nerve cells and their interactions in the nervous system of the wall of the mantle cavity and mantle derivatives - gills, siphon, and osphradia - of the marine prosobranch gastropod mollusks Buccinum undatum and Littorina littorea. The results are discussed along with our own previously obtained data on the organization of the osphradial sensory organs and the afferent elements of the mantle cavity wall in other prosobranch mollusks - the terrestrial Pomatia elegans and the freshwater Viviparus contectus and Pomacea paludosa. Using the nervous system of the complex of mantle organs of prosobranch mollusks as examples, the structural features and evolutionary trends of the afferent part of the visceral nervous system of gastropods are discussed.

[Localization of NADPH diaphorase in the central nervous system of the bivalve mollusc Cristaria tuberculata]

By histochemical and electron histochemical methods, NADPH-diaphorase was discovered in neurons and their processes of all ganglia of the central nervous system (CNS) of Cristaria tuberculata. Small cells predominated among neurons containing NADPH-diaphorase. Ultrastructural localization of the enzyme was detected on the perinuclear membrane and membranes of endoplasmic reticulum, cytoplasmic granules and cytosol. In the majority of cells, the reaction product was commonly found in cytoplasmic granules-cytosomes. We studied peculiarities of synaptic contacts between nitrogen oxide synthesizing neurons and their processes. In active synaptic areas, a sediment was discovered on the internal surface of pre- and postsynaptic membranes.

[Somatic polyploidy in neurons of the gastropod mollusca. III. Mitosis and endomitosis in the postnatal development of neurons in the Succinea snail central nervous system]

General morphology of chromatin, the number of chromosomes and chromocenters in normal condition and at the increase of bivalent cation (Ca2+, Mg2+) concentration were studied with the purpose to reveal mechanisms of polyploidization of neuron nuclei in the snail Succinea lauta (Gastropoda, Pulmonata). The morphology of nuclei was studied on squashed preparations. Normal diploid mitoses are described in the cerebral ganglia. A possibility is supposed that part of neurons or neuroblasts in the central nervous system (CNS) of succineid snail may divide mitotically. It has been shown that the basic mechanism of neuron postnatal growth is endomitotic polyploidization of nuclei. The transition from ordinary mitosis to polyploid cycles occurs via restitutional (polyploidizing) mitosis (4c2n-->4c4n). The next endocycles are carried out by means of classic endomitosis up to reaching the highest ploidy levels--4096n--16,384n. The study of general morphology of chromatin and chromocenters at normal condition and at artificial compactization enabled us to exclude any probability of polyteny in the CNS of lauta.

[Localization of NADPH diaphorase in central nervous system of the chiton Leptochiton assimilis in normal conditions and during hypoxia]

By light and electron microscope histochemical and cytochemical methods, the localization and activity of NADPH-diaphorase (NADPH-d) were studied in the central nervous system (CNS) of the chiton in control and after hypoxia. After acute hypoxia, the enzymatic activity increased in all regions of CNS. At a chronic hypoxia, the activity of NADPH-d decreased to remain, however, higher than in control. Ultrastructural studies confirmed the availability of structural changes in neurons, and shifts in the activity of NADPH-d in control and in experimental mollusks. The elevated enzymatic activity revealed in this study may be due to the fact that these mollusks have been evolutionary adapted to a periodical oxygen deficiency.

Microstructure of Monoplacophora (Mollusca) shell examined by low-voltage field emission scanning electron and atomic force microscopy

The shell of Micropilina arntzi (Mollusca: Monoplacophora), a primitive molluscan class, was examined by using field emission scanning electron microscopy (FESEM) at low voltage and atomic force microscopy (AFM). The use of these two techniques allowed the observation of fine details of Micropilina arntzi shell and contributed to bring new features concerning the study of molluscan shell microtexture. Imaging with low-voltage FESEM provided well-defined edge contours of shell structures, while analyzing the sample with AFM gave information about the step height of stacked internal structures as well as the dimension of the particles present in their surface at a nanometric level. The shell microstructure of Monoplacophora species presents different patterns and may be a taxonomic implication in the systematic studies of the group.

A single mitochondrial lineage is shared by morphologically and allozymatically distinct freshwater Corbicula clones

Despite that the exotic invasion and rapid range expansion of Asian freshwater Corbicula into new environments have been of intensive research topic in freshwater ecology, the genetic structures of freshwater Corbicula in its native range remain poorly understood. In this study, the genetic structures of two Korean freshwater Corbicula clonal lineages were characterized by cross-referencing the nuclear genomic structures with mtDNA sequence analysis. In spite of substantial genetic differences (Nei's D = 0.363-0.372) and a pronounced level of fixed allelic distinctions (in six of 20 allozyme loci) between Corbicula lineages, no lineage-specific mtDNA differentiation was observed. The evident disjunction between mtDNA sequences and nuclear genomes is a compelling evidence for the existence of interspecific nuclear hybrid genome structures, comprising different combinations of paternal and maternal contributions. This unusual novel finding is the first case demonstrating that morphologically and allozymatically distinct, yet mitochondrially identical clonal lineages exist in the genus Corbicula. However, we could not find the ancestral species for these two clonal lineages in the present study, and the answer for this question must wait until the genetic structure of Asian Corbicula taxa is fully characterized.

Mollusc larval shell formation: amorphous calcium carbonate is a precursor phase for aragonite

The larval shells of the marine bivalves Mercenaria mercenaria and Crassostrea gigas are investigated by polarized light microscopy, infrared spectroscopy, Raman imaging spectroscopy, and scanning electron microscopy. Both species contain similar shell ultrastructures. We show that larval shells contain amorphous calcium carbonate (ACC), in addition to aragonite. The aragonite is much less crystalline than non-biogenic aragonite. We further show that the initially deposited mineral phase is predominantly ACC that subsequently partially transforms into aragonite. The postset juvenile shell, as well as the adult shell of Mercenaria also contains aragonite that is less crystalline than non-biogenic aragonite. We conclude that ACC fulfills an important function in mollusc larval shell formation. It is conceivable that ACC may also be involved in adult shell formation.

Mollusc larval shell formation: amorphous calcium carbonate is a precursor phase for aragonite

The larval shells of the marine bivalves Mercenaria mercenaria and Crassostrea gigas are investigated by polarized light microscopy, infrared spectroscopy, Raman imaging spectroscopy, and scanning electron microscopy. Both species contain similar shell ultrastructures. We show that larval shells contain amorphous calcium carbonate (ACC), in addition to aragonite. The aragonite is much less crystalline than non-biogenic aragonite. We further show that the initially deposited mineral phase is predominantly ACC that subsequently partially transforms into aragonite. The postset juvenile shell, as well as the adult shell of Mercenaria also contains aragonite that is less crystalline than non-biogenic aragonite. We conclude that ACC fulfills an important function in mollusc larval shell formation. It is conceivable that ACC may also be involved in adult shell formation.

Magnetic anisotropy of the radula of chiton Acanthochiton rubrolinestus LISCHKE

The magnetic anisotropy of the whole radula, the major lateral radula teeth, and magnetic material in the major lateral radula teeth of the chiton Acanthochiton rubrolinestus LISCHKE have been studied by a magnetic torque meter and superconducting quantum interference device (SQUID) magnetometer. The length and width axes of the teeth are the easily magnetized axes, while the thickness axis is difficult to magnetize. The width and thickness axes of the radula are the easily magnetized axes, and the length axis is difficult to magnetize. The measurement results of the whole radula and the major lateral radula teeth agree well with each other. The magnetic anisotropy of the magnetic material is given as well as a possible distribution of the magnetic material in the major lateral radula teeth.

Fine structural study of the spermatogenic cycle in Pitar rudis and Chamelea gallina (Mollusca, Bivalvia, Veneridae)

A comparative ultrastructural study of spermatogenesis was performed in the bivalve molluscs Pitar rudis and Chamelea gallina (Veneridae) from Turkey. Sertoli cells appeared to be rich in glycogen, lipid droplets and germ-cell phagolysosomes. Premeiotic cells exhibited nuage and a flagellum, with the Golgi complex and the rough endoplasmic reticulum originating proacrosomal vesicles during the pachytene stage. In round spermatids, the acrosomal vesicle migrated linked to the plasma membrane. In P. rudis, the acrosomal vesicle base formed a thin expansion that attached to the nuclear apex and was associated with development of the perforatorium. The cap-shaped acrosomal vesicle then differentiated into external and internal regions, and also into a small apical light region, although some cells exhibited an apical extension of the external component. On the contrary, two lateroapical light pouches developed in C. gallina. During spermiogenesis, chromatin became fibrillar and then condensed while the nucleus turned conical shaped in P. rudis or slightly curved in C. gallina. In P. rudis, the midpiece contained glycogen and four mitochondria, although five mitochondria were sometimes observed, whereas in C. gallina the midpiece contained four mitochondria. Comparison with other members of Veneroida shows a common ectaquasperm type, but novel findings in acrosome biogenesis.

Neurogenesis in the mossy chiton, Mopalia muscosa (Gould) (Polyplacophora): evidence against molluscan metamerism

Neurogenesis in the chiton Mopalia muscosa (Gould, 1846) was investigated by applying differential interference contrast microscopy, semithin serial sectioning combined with reconstruction techniques, as well as confocal laser scanning microscopy for the detection of fluorescence-conjugated antibodies against serotonin and FMRFamide. The ontogeny of serotonergic nervous structures starts with cells of the apical organ followed by those of the cerebral commissure, whereas the serotonergic prototroch innervation, pedal system, and the lateral cords develop later. In addition, there are eight symmetrically arranged serotonergic sensory cells in the dorsal pretrochal area of the larva. FMRFamide-positive neural elements include the cerebral commissure, specific "ampullary" sensory cells in the pretrochal region, as well as the larval lateral and pedal system. In the early juvenile the cerebral system no longer stains with either of the two antibodies and the pedal system lacks anti-FMRFamide immunoreactivity. Outgroup comparison with all other molluscan classes and related phyla suggests that the cord-like, nonganglionized cerebral system in the Polyplacophora is a reduced condition rather than a primitive molluscan condition. The immunosensitivity of the pedal commissures develops from posterior to anterior, suggesting independent serial repetition rather than annelid-like conditions and there is no trace of true segmentation during nervous system development. Polyplacophoran neurogenesis and all other available data on the subject contradict the idea of a segmented molluscan stem species.

Anatomical correlates of venom production in Conus californicus

Like all members of the genus, Conus californicus has a specialized venom apparatus, including a modified radular tooth, with which it injects paralyzing venom into its prey. In this paper the venom duct and its connection to the pharynx, along with the radular sac and teeth, were examined using light and transmission electron microscopy. The general anatomy of the venom apparatus resembles that in other members of the genus, but several features are described that have not been previously reported for other species. The proximal (posterior) quarter of the venom duct is composed of a complex epithelium that may be specialized for active transport rather than secretion. The distal portion of the duct is composed of a different type of epithelium, suggestive of holocrine secretion, and the cells display prominent intracellular granules of at least two types. Similar granules fill the lumen of the duct. The passageway between the lumen of the venom duct and pharynx is a flattened branching channel that narrows to a width of 10 micro m and is lined by a unique cell type of unknown function. Granular material similar to that in the venom duct was also found in the lumen of individual teeth within the radular sac. Mass spectrometry (MALDI-TOF) demonstrated the presence of putative peptides in material derived from the tooth lumen, and all of the more prominent species were also evident in the anterior venom duct. Radular teeth thus appear to be loaded with peptide toxins while they are still in the radular sac.

Comparison of the soluble matrices of the calcitic prismatic layer of Pinna nobilis (Mollusca, Bivalvia, Pteriomorpha)

The calcitic prisms of the outer layer of the shell of Pinna nobilis, surrounded by thick organic walls, contain a soluble intracrystalline matrix. The structure and composition of the outer interprismatic walls are not well known. The current viewpoint is they are composed of an insoluble matrix. Another thick organic structure, the interlamellar sheet of the nacreous layer, is composed of insoluble and soluble matrices. The composition of two sets of soluble organic matrices from the calcitic layer of Pinna nobilis, extracted with and without the organic walls are compared. According to the various analyses (SEM and AFM, UV and FTIR spectrometry, HPLC, electrophoreses, XANES), the main characteristics of the two matrices are similar, but not identical. Thus, the organic walls contain soluble components. However, the three-layered structure of the interlamellar sheet of the nacreous layer has not been observed.

Larval and metamorphic development of the foregut and proboscis in the caenogastropod Marsenina (Lamellaria) stearnsii

The specialized, postmetamorphic feeding structures of predatory caenogastropods evolved by changes to an ancestral caenogastropod developmental program that generated a planktotrophic larval stage followed by a herbivorous postmetamorphic stage. As part of a program of comparative studies aimed at reconstructing these developmental changes, I studied the development of the postmetamorphic feeding system of Marsenina stearnsii using histological sections for light microscopy and scanning and transmission electron microscopy. The feeding system of this species has two very different designs during ontogeny. The larval system uses ciliary effectors to capture and ingest microalgae, whereas the juvenile/adult system includes a proboscis, jaws, and radular apparatus for predation on ascidian zooids. The postmetamorphic foregut begins to develop during the early larval phase, but the anlagen does not interfere with larval feeding because it develops as an increasingly elaborate outpocketing from the ventral wall of the larval esophagus. At metamorphosis, an opening is created in the anterior tip of the prospective, postmetamorphic buccal cavity and the margins of this opening anneal with the metamorphically remodeled lips of the larval mouth. This process exposes the jaws, which differentiate within the buccal cavity prior to metamorphosis. As a working hypothesis, I suggest that rupture of the buccal cavity to the outside at metamorphosis was selected as a mechanism to allow precocious development of jaws in species where jaws enhanced feeding performance by young juveniles. The larval esophagus of M. stearnsii appears to be completely destroyed at metamorphosis. Larval esophageal cells have distinctive apical characteristics (cilia, blebbed microvilli, stacks of lamellae within the glycocalyx) and no cells having this signature persist through metamorphosis. Development of the proboscis and proboscis sac, which begins prior to metamorphosis, conforms to previous descriptions of pleurembolic proboscis development, although an acrembolic proboscis has been ascribed to members of the Lamellaroidea.