Survival and repair of surgical and natural shell damage in the articulate brachiopod Terebratulina retusa (Linnaeus)

Living specimens of Terebratulina retusa from the Firth of Lorn, Scotland, were surgically damaged by drilling 2 mm diameter holes or narrow slits one cm long in the anterior portion of one valve, by bevelling the anterior margin of both valves, or by amputation of the anterior third of one valve. These injuries to the shell and mantle simulated the type of repaired shell damage seen in Paleozoic species, i.e., scalloped, divoted, cleft, and embayed valves. Less than ten percent of the 200 damaged specimens survived until the 25th week after surgery. Specimens of T. retusa showed the ability to repair drill holes, slits, and bevelled anterior shell regions, but not the most severe damage, i.e., amputations of the anterior third of one valve. Shell‐repair was initiated in the fourth week after surgery by the development of a membrane across the wound. The development of caeca in the new shell layer secreted to plug the drill holes became apparent by the eighth week. The punctate pattern was complete in the new, translucent shell material of bevelled and drilled specimens by the 25th week following surgery. Failure of any specimens to survive amputation of the anterior portion of a valve for more than seven weeks after surgery, and the absence of initiation of the repair process, suggests that terebratulids do not have the tolerance for, nor the ability to repair, the severe injuries (embayed valves) which were sustained and mended by extinct strophomenids.     

Manganese in the shell of Centropyxis (Rhizopodea: Protozoa)

Summary The proteinaceous shells of Centropyxis hirsuta contain a relatively high concentration of manganese in an amorphous state. The concentrations of manganese fill the alveoli which are characteristic of the shell structure. Observations based on cultured animals and subsequently examined by X-ray diffraction, a solid state energy dispersive X-ray analyser, and an analytical electron microscope, lead to the conclusions that manganese is selectively absorbed by Centropyxis hirsuta and deposited in the shell.     

Shell differentiation and engrailed expression in the Ilyanassa embryo

 We have used in situ hybridization and immunocytochemistry to study the expression of the engrailed-related gene, Ily-en in embryos of the marine mud snail Ilyanassa obsoleta. We find that Ily-en is only expressed in shell gland cells. Only mRNAs localized in the shell gland hybridize to an antisense probe of the Ily-en homeobox. Similarly, only shell gland cells or shell-forming cells are stained by the monoclonal antibody 4D9, which was raised to the engrailed-class protein from Drosophila. Ilyanassa embryos made deficient in vegetal cytoplasm by removing the third polar lobe fail to differentiate an organized external shell. They do however make some randomly oriented internal shell fragments in which Ily-en is expressed. Because Ily-en is expressed in shell gland cells of both normal and lobeless embryos, we conclude that the determinant(s) required for Ily-en expression are not exclusively localized in the polar lobe. Received: 16 October 1997 / Accepted: 9 January 1998     

Structure and formation of the adventitious tube of the Japanese watering-pot shell Stirpulina ramosa (Bivalvia, Anomalodesmata, Clavagellidae) and a comparison with that of the Penicillidae

Abstract. Stirpulina ramosa is the only extant endobenthic representative of the Clavagellidae and is restricted to the waters of Japan. A single intact adventitious tube of this species has been obtained and its structure is described. The right valve is 16 mm long and located within the adventitious tube. It has an opisthodetic ligament located on resilifers. There are anterior and posterior adductor muscle scars, a thick pallial line, and pallial and pedal gape (right valve only) sinuses. The left shell valve is but 9 mm long and is united into the fabric of the adventitious tube via the intermediary of a shelly saddle. Internally, only the anterior adductor muscle scar and a small element of the pallial line scar are identifiable on the left valve. The posterior adductor and the rest of the pallial line scar (including a pallial sinus) are, remarkably, located on the adventitious tube beyond the shell valve margin. The adventitious tube of S. ramosa is formed in a manner wholly dissimilar from that of Brechites vaginiferus (Penicillidae). In B. vaginiferus, the tube is secreted as a single entity from the general outer mantle surface, including the siphons, covering the body. As a consequence, both shell valves are incorporated into the structure of the tube and the watering pot is bilaterally symmetrical. In S. ramosa, the tube and watering pot are secreted from the mantle margin and surface surrounding and extending from the left shell valve, so that only the left valve is incorporated into its structure. A dorsally derived mantle element is progressively extended over to the right side of the body, meeting a ventrally derived counterpart that passes beneath it, forming a pleat in the calcareous structure of the right side of the tube that they secrete. This pleat extends into the complex of watering‐pot tubules and forms the pedal gape. The watering pot is thus Ω shaped. The ventrally derived mantle element forms a sinusoidal crest on the right‐hand base of the watering pot, creating a pedal gape sinus scar on the right valve. The Clavagellidae radiated widely in the Mesozoic, leaving behind a rich fossil record for Stirpulina. Only S. ramosa, however, has survived until the present. In contrast, the Cenozoic Penicillidae has a poor fossil record, but there is a rich variety of extant endobenthic watering‐pot shells. It has been argued hitherto that the two families represent a remarkable example of convergent evolution. In view of the success of the Penicillidae and thus the endobenthic, tube‐dwelling lifestyle, however, it is hard to understand why Stirpulina has largely died out—even S. ramosa being known by but one or two specimens. A study of the anatomy of S. ramosa might one day answer this question.     

Haemocyte response associated with induction of shell regeneration in the deep-sea vent mussel Bathymodiolus azoricus (Bivalvia: Mytilidae)

This study reports on the haemocyte responses after induction of shell regeneration in the hydrothermal mussel Bathymodiolus azoricus. Haemolymph was drawn from live mussels collected at Menez Gwen hydrothermal vent site (850 m depth) at the Mid Atlantic Ridge (MAR) and was compared with those collected following laboratory acclimatisation (1 atm and Ca-rich algal diet) and also with induced specimen for up to 30 days. Simultaneously, histological changes in mantle micro-morphology with the histochemical detection of Ca mobilisation in tissues were conducted.On the basis of light- and transmission electron microscopy, it is concluded that the physiological equipment involved in shell regeneration in the deep sea bivalve closely resembles that in littoral mytilids, a group that B. azoricus is closely related. This in spite of previously alleged molecular and cellular adaptations to extreme conditions typical at deep sea hydrothermal vents. Three types of blood cells were identified sharing various morphological similarities with those in many non-vent bivalves. Significant increase in the number of circulating haemocytes was detected from day 5 after induction shell regeneration. It is suggested that the increase may be a result of migration of haemocytes from the connective tissue, probably to the shell growth frontline. It is alleged that a first peak in haemocyte number is a non-specific immune response related wound healing, which renders changes in the pallial fluid that are favourable for CaCO₃ deposition. The conspicuous presence of an unidentified, acid soluble, highly refractive structure in the haemolymph of induced mussels was detected, which may play a role in Ca nucleation.This study has set the stage for investigations underway on the influence of hydrostatic pressure on shell biomineralisation in B. azoricus subjected to post-capture hyperbaric simulations.     

Opioid systems,behavioral thermoregulation and shell polymorphism in the land snail,Cepaea nemoralis

Summary Numerous ecological studies have dealt with the shell color and banding polymorphism of the land snail Cepaea nemoralis. The present field and laboratory investigations focus on the roles of opioid systems in modulating the thermal preferences and behavioral thermoregulation of various morphological types of Cepaea. Evidence is presented that differences in opioid modulation of the thermal responses of Cepaea are associated with shell polymorphism. It is shown that the effects of the prototypic opiate agonist, morphine, and antagonist, naloxone, on behavioral thermoregulation in Cepaea vary with the shell banding pattern and thermal microhabitat. In both the field and laboratory, morphine (0.10, 1.0 and 10 g per snail) caused significant dose- and time-dependent increases in the temperatures selected by various morphological types of Cepaea. The palest shell type (yellow, unbanded) with the highest basal preferred temperature displayed the greatest response to morphine, the shell type (yellow, 2-banded) with an intermediate basal preferred temperature showed an intermediate response to morphine, and the darkest shell type (yellow, 5-banded) with lowest basal preferred temperature showed the least increase in preferred temperature after administration of morphine. These effects of morphine were blocked and reversed by naloxone (1.0 g), with the opiate antagonist by itself (1.0 and 10 g) causing a significant decrease in behaviorally selected temperatures. The unbanded and 2-banded morphs displayed significantly greater decreases in preferred temperatures after treatment with naloxone than did the 5-banded morph, which showed minimal responses. It is suggested that these differences in opioid modulation of thermal preferences and behavioral thermoregulation may contribute to the polymorphic thermal preferences of natural populations of Cepaea.Abbreviations B yellow five-banded shell type - I yellow two-banded shell type - U yellow unbanded shell type     

Swimming behavior and morphometry of the file shell Limaria fragilis

Swimming has evolved in only a few orders of Bivalves. In this study, the behavior, morphometry, and mechanics of swimming in the file shell Limaria fragilis were characterized and compared to the better understood scallops. Absolute swimming speed (cm?sec^?1) increased with increasing shell height, although relative swimming speed (body lengths?sec^?1) did not covary with shell height. The increase in absolute swimming speed was due to an increase in the distance covered during each valve clap as clap distance (cm?clap^?1) also increased with shell height while clapping frequency (claps?sec^?1) did not covary with animal size. Limaria fragilis displayed a variety of morphological changes related to size. Shell length was negatively allometric with shell height indicating the shell became proportionately slimmer in larger animals. Dry shell mass was negatively allometric with shell height, while both dry adductor muscle mass and dry mantle + tentacle mass were positively allometric. Autotomy of mantle tentacles significantly decreased clap distance by 13% without affecting clapping frequency or swimming speed.     

The shell matrix of the pulmonate land snail Helix aspersa maxima

In mollusks, the shell mineralization process is controlled by an array of proteins, glycoproteins and polysaccharides that collectively constitute the shell matrix. In spite of numerous researches, the shell protein content of a limited number of model species has been investigated. This paper presents biochemical data on the common edible land snail Helix aspersa maxima, a model organism for ecotoxicological purposes, which has however been poorly investigated from a biomineralization viewpoint. The shell matrix of this species was extracted and analyzed biochemically for functional in vitro inhibition assay, for amino acid and monosaccharides compositions. The matrix was further analyzed on 1 and 2D gels and short partial protein sequences were obtained from 2D gel spots. Serological comparisons were established with a set of heterologous antibodies, two of which were subsequently used for subsequent immunogold localization of matrix components. Our data suggest that the shell matrix of Helix aspersa maxima may differ widely from the shell secretory repertoire of the marine mollusks studied so far, such as the gastropod Haliotis or the pearl oyster Pinctada. In particular, most of the biochemical properties generally attributed to soluble shell matrices, such as calcium-binding capability, or the capacity to interfere in vitro with the precipitation of calcium carbonate or to inhibit the precipitation of calcium carbonate, were not recorded with this matrix. This drastic change in the biochemical properties of the landsnail shell matrix puts into question the existence of a unique molecular model for molluscan shell formation, and may be related to terrestrialisation.     

The effects of shell size and coil orientation on reproduction in female hermit crabs, Clibanarius vittatus

We investigated the effects of shell coil orientation and shell size on reproduction in field populations of the hermit crab, Clibanarius vittatus. Females were collected in the intertidal in Beaufort, NC. Shell parameters were measured and size (cephalothorax length) and reproductive status were determined for 70 females occupying Busycon shells. Crabs were categorized as berried (eggs on the pleopods), mature ovaries, or non-reproductive (no eggs). For berried females, the number of eggs was recorded. By offering a separate group of females access to empty shells, it was possible to calculate optimal shell size and the deficit in shell size for field-collected animals.Females that were berried were in shells closer to the optimal shell size than females with mature ovaries, both for shell weight and shell volume. And females with mature ovaries were in shells that were closer to the optimal size than females that were non-reproductive. For both categories of females without eggs on the pleopods, the majority of females were in shells that were too big (in weight and internal volume). While the percentage of berried females did not differ between dextral (Busycon carica) and sinistral (Busycon sinistrum) shells, the non-reproductive females had a much smaller deficit in volume in sinistral shells compared to dextral shells. For berried females, there was no relationship between the magnitude of their shell deficit and the number of eggs carried. Our results suggest that reproduction is inhibited when females occupy shells sufficiently greater than the optimal shell size.     

The cytology of the testaceous rhizopod Lesquereusia spiralis (Ehrenberg) Penard. I. Ultrastructure and shell formation

Ultrastructure and shell formation in the testaceous ameba, Lesquereusia spiralis, were investigated with both scanning and transmission electron microscopy and X-ray microanalysis. The nucleus, surrounded by a fibrous lamina, contains multiple nucleoli. The cytoplasm, containing a well developed granular endoplasmic reticulum, also contains remnants of starch granules in stages of digestion. Spherical aggregates of ribosome-like particles may be seen. Golgi complexes seem to produce both a nonordered fibrous material and an electron dense vesicle. Only the latter appears to bleb off from the Golgi complex. X-ray microanalysis demonstration of silicon in Golgi vesicles and in some dense vesicles suggests that the fibrous component of the cisternae may take up and concentrate silica to form the electron-dense component of the vesicles. Membrane-bound siliceous crystals are often seen adjacent to the Golgi, suggesting either a Golgi origin or platelet formation in vesicles after release from the Golgi complex. Both electron-dense bodies and siliceous platelets are released from the cell by a process similar to apocrine secretion and may be seen outside the cell in route to the shell during shell morphogenesis. Shell development involves fusion of electron-dense bodies to form a matrix, positioning of siliceous platelets in this matrix parallel to the shell surface, and development of a system of matrix chambers. A particulate glycoconjugate is released to the shell surface upon rupture of the matrix chamber.     

3-Decanol in the haemolymph of the hermit crab Clibanarius vittatus signals shell availability to conspecifics

Hermit crabs with poor fitting shells are chemically attracted to dying gastropods and conspecifics where a shell may become available. For land hermit crabs, the shell cue is a volatile compound found in the haemolymph. Based on this knowledge, we tested the hypothesis that shell investigation behavior in aquatic hermit crabs, the ancestral predecessors of terrestrial hermit crabs, is also triggered by volatile cues. Volatile compounds from haemolymph of Clibanarius vittatus and Pagurus pollicaris and brachyuran decapod crustaceans were purged from a water-haemolymph solution, trapped in seawater and tested for induction of shell investigation behavior with juvenile C. vittatus. Only volatiles from C. vittatus haemolymph stimulated shell investigation. Volatile compounds were isolated from haemolymph by headspace solid-phase microextraction (SPME) and analyzed by coupled gas chromatography-mass spectrometry (GC-MS). Two prominent compounds were identified, 3-decanol, which was unique to C. vittatus haemolymph, and 2-ethyl-1-hexanol, which was present in the haemolymph of all 4 crustacean species. In shell investigation bioassays, 3-decanol from C. vittatus haemolymph stimulated shell investigation behavior, while 2-ethyl-1-hexanol did not. In bioassays with synthetic 1-, 2-, 4-, and 5-decanol, shell investigation behavior was evoked by 1-decanol, 5-decanol and 3-undecanol. There was no response to 2- and 4-decanol. The response of C. vittatus to volatile shell cues supports the hypothesis that volatile cue detection evolved prior to the occupation of terrestrial niches by crustaceans.     

Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny

Popov, L.E., Bassett, M.G., Holmer, L.E., Skovsted, C.B. & Zuykov, M.A. 2010: Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny. Lethaia, Vol. 43, pp. 323–333. Well preserved specimens of the Early Palaeozoic craniiform brachiopods Orthisocrania and Craniops retain clear evidence of a lecithotrophic larval stage, indicating the loss of planktotrophy early in their phylogeny. The size of the earliest mineralized dorsal shell was <100 μm across, and the well preserved shell structure in these fossil craniiforms allows their earliest ontogeny to be compared directly with that of living Novocrania, in which the first mineralized dorsal shell (metamorphic shell) is secreted only after settlement of the lecithotrophic larvae. Immediately outside this earliest shell (early post‐metamorphic or brephic shell) and in the rest of the dorsal valve the primary layer in both fossil and living craniiforms has characteristic radially arranged laths, which are invariably lacking in the earliest dorsal shell. The ventral valve of the fossil specimens commonly preserves traces of an early attachment scar (cicatrix), which is equal in size to the dorsal metamorphic shell, and the brephic post‐metamorphic ventral valve also has a primary shell with radially arranged laths. However, a primary shell with radial laths is completely lacking in the ventral valve of living Novocrania, indicating that heterochrony may have been involved in the origin of the encrusting mode of life in living craniids; the entire ventral valve of Recent craniids (with the possible exception of Neoancistrocrania) may correspond to the earliest attachment scar of some fossil taxa such as Orthisocrania. It is also probable that the unique absence of an inner mantle lobe as well as the absence of lobate cells in Novocrania could be the result of heterochronic changes. The dorsal valve of both fossil and living craniiforms has a marked outer growth ring, around 500 μm across, marking the transition to the adult, and a significant change in regime of shell secretion. The earliest craniiform attachment is considered to be homologous to the unique attachment structures described recently in polytoechioids (e.g. Antigonambonites) and other members of the strophomenate clade. However, unlike the craniiforms, polytoechioids and strophomenates all have planktotrophic larvae, and planktotrophy is most probably a plesiomorphic character for all Brachiopoda. □Brachiopoda, Craniiformea, Early Palaeozoic, ontogeny, phylogeny.     

Prefabrication of shell ornamentation in the bivalve Laternula

The minute, cone-like spikes which cover the valve surfaces of Laternula arc formed by the mantle in advance of the growing shell margin and are subsequently incorporated into the calcarcous shell. This 'prefabrication' process allows the formation of a prismatic spike ultrastructure distinct from other layers of the nacro-prismatic shell and provides ornamentation to the otherwise uncalcified ventral surface. A consideration of a number of morphologic variables, including the mechanism of shell construction, suggests that spikes function to increase the skin friction of the valve surfaces and thereby promote a stable life position. Variations on Laternula's shell construction mechanism arc found throughout the Pandoracea and possibly larger taxonomic groupings.     

Identification of candidate AFLP markers for shell color of the Pacific oyster (Crassostrea gigas) under artificial selection

The shell color of the Pacific oyster (Crassostrea gigas) is a desirable trait, but only a few genetic studies on shell color have been documented. Through successive selective breeding, four shell color variants of white (W), gold (G), black (B) and purple (P) C. gigas have been developed. The amplified fragment length polymorphism (AFLP) technique was used to scan the genomes of the four variants with different shell colors and one wild population (C) to identify candidate markers for shell polymorphism. Fifteen AFLP primer combinations were used, 1079 loci were scored as polymorphic loci, and the percentage of polymorphic bands was 95.5%. In the gold, white, black, purple and wild populations, the percentages of polymorphic loci were estimated to be 90.5% (G), 90.0% (W), 91.1% (B), 95.3% (P) and 93.2% (C); the expected heterozygosity values were 0.3115 (G), 0.3044 (W), 0.3102 (B), 0.3285 (P) and 0.3105 (C). The white shell variant was observed to have slightly lower genetic diversity than others, with a F_ST value of 0.1483. These results indicated that the four different shell color variants had high genetic diversity and that the genetic differentiation of populations mostly results from genetic diversity of individuals within populations. Furthermore, 11 outlier loci were considered candidate markers for shell color. This work provides new insights on relationships among color variants of C. gigas.     

Contributions of the surface of the root tip to the growth of Zea roots in soil

The development of the epidermal layer of roots of Zea is traced from the quiescent centre to the zone where root hairs develop. In the zone of cell division a three layered coat forms on the outside of the epidermal cells consisting of the outer epidermal walls, overlaid by a two-layered pellicle composed of a thick fibrillar inner layer of polysaccharide, and a thin fibrillar outer layer of protein. The epidermal cells divide several times in the same longitudinal file but rarely across a radius to give a new longitudinal file. Thus, the radial walls become much thicker than all but the original transverse walls, and packets of up to 32 daughter cells derived from a single initial may be distinguished. The pellicle develops during these divisions as a continuum over the outer walls of the daughter cells. It is proposed that the pellicle provides a stiffening to the forward end of the root which permits it to penetrate soil without bending. Support for this hypothesis is shown by the Zea mays mutant Ageotropic in which the pellicle is absent, the epidermal surface is disorganized, and which grows crookedly through soil. In the zone of extension growth of normal roots of two Zea species the pellicle thins and disappears. Circumferential strips of the pellicle were peeled off the young epidermal cells and could be stretched to twice their length. This deformation is partly the result of the pellicle stretching and breaking above the attachments of the radial walls. After normal thinning of the pellicle, detachment of the radial walls at their outer ends produces a corrugated surface in the proximal zone of the root tips. In dicotyledons (e.g., soybean), there is no similar pellicle, but a stiff root tip is produced by a long multi-layered root cap, the proximal portion of which covers the elongating epidermal surface.     

Influence of prior experience on shell selection by the white spotwrist hermit crab Pagurus criniticornis (Crustacea: Paguridae)

Individuals of Pagurus criniticornis in a free-choice situation were experimentally tested under different laboratory conditions. In order to assess the effect of recently occupied shells on the size- and type-preference by hermit crabs, individuals were held for 30 days under one of the following two conditions: (1) excess of shells and (2) absence of shells. The crabs were then allowed to select shells from a wide array of empty gastropod shells of the two most-occupied species, as observed previously in the field: Cerithium atratum and Morula nodulosa. Preferred shell type (species) and size (shell aperture width and length) were correlated with hermit-crab size. The crabs showed a strong (100%) preference for C. atratum shells, demonstrating that recent and past experience did not influence either shell-type or shell-size preferences in this pagurid. Handling editor: K. Martens     

Effect of estrogen and its antagonist on the expression of arginine vasotocin (AVT) and its oxytocic-like receptor VT3 in the shell gland of Japanese quail, Coturnix coturnix japonica

Avian neurohypophysial hormone arginine vasotocin (AVT) is known to regulate shell gland contractility during oviposition. While studying the role of estrogen in the expression and regulation of AVT and its oxytocic-like receptor VT3, using in situ hybridization and immunohistochemistry, it was observed that the expression of AVT and its receptor was not detected in the shell gland of sexually immature Japanese quail. However, administration of estrogen to these birds not only stimulates the growth and activity (as assessed by increased mucosal fold length, total protein content and alkaline phosphatase level) of the shell gland but also upregulates the expression of AVT and VT3. Further, administration of estrogen antagonist tamoxifen to sexually mature bird shows opposite results. On the other hand, localization of ir-AVT, observed in the ovary of sexually mature bird, was not detected in the estrogen treated sexually immature quail. It is concluded that estrogen not only affects the growth and differentiation of avian oviduct, but also regulates the expression of shell gland AVT and its receptor VT3. Present findings suggest that the locally synthesized AVT acts in a paracrine way to upregulate VT3 receptor and thus facilitates the endocrine function of neurohypophysial AVT during oviposition.     

Systematics, shell structure and affinities of the Palaeozoic Problematicum Cornulites

The genus Cornulites, with the type species C. serpularius Schlotheim, 1820, from the Silurian of Gotland, comprises annulated, conical or tubular calcite shells, often found attached to the hard parts of other organisms. No consensus has ever been reached over the zoological affinities of the taxon, and no examples of soft‐part preservation are known: detailed examination of shell structures and growth patterns provide the only means of assessing its systematic position. Using transverse and longitudinal thin sections of C. serpularius Vine, 1882, and C. cellulosus sp. nov. , from the Much Wenlock Limestone Formation of England, the shell structure of Cornulites is shown to be lamellar, but with conspicuous internal chambers (camerae) at the apical end of the shell and, particularly in C. cellulosus, numerous smaller vacuities (cellulae) between the lamellae in the apertural shell region. Growth of the shell was by the secretion of low‐magnesian calcite increments within one another, giving a cone‐in‐cone structure, with the prominent development of cellulae in C. cellulosus probably a constructional feature relating to an upright life position. By comparison of morphology and shell structure with other taxa, the zoological affinities of Cornulites are re‐examined; previously suggested affinities with annelids, foraminifers, molluscs and poriferans can be ruled out. Specific shell structures, most notably pseudopuncta similar to those of bryozoans and brachiopods, have led some recent workers to interpret cornulitids as lophophorates. However, it is shown that they can be interpreted alternatively as solitary, aseptate members of the stem‐Zoantharia (Cnidaria: Anthozoa). Four cornulitid species are recognized in the Much Wenlock Limestone Formation: C. cellulosus sp. nov. , C. gremialis sp. nov. , C. scalariformis and C. serpularius. In the absence of the type material, C. serpularius is here restricted to cornulitids closely resembling the specimens originally figured by Schlotheim. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 150 , 681–699.