Shell Morphogenesis Research Articles

Development mechanics of retractor muscles and the “Dead Spiral Model” in gastropod shell morphogenesis

Development mechanics of retractor muscles and the “Dead Spiral Model” in gastropod shell morphogenesis

Sectorial expansion and shell morphogenesis in molluscs

Checa, A. 1991 01 15: Sectorial expansion and shell morphogenesis in molluses. Lethaia. Vol. 24, pp. 97–114. Oslo. ISSN 0024–1164. Any coiled shell can be described as a series of independent helicospirals that join homologous points along the shell surface. The cross-section is therefore seen as a set of points. obtained at its intersection with the helicospirals. Any cross-sectional sector contained between two adjacent points is capable of expanding or contracting during the development and a differential parameter (L'/L) has been devised to quantify this expansion rate. The morphometrics so obtained is here called sectorial expansion analysis. This analysis and other related procedures have been applied on cross-sections and apertures in selected Molluxa with the aim of evaluating the incidence of sectorial expansions on shell shape. Those parameters affecting whorl expansion rate and whorl overlapping may be directly modified by sectorial expansions. Changes in the mode of coiling (curvature and torsion) often, but not always, involve sectorial expansions, perhaps as a constructional feature. This approach reveals the advantages and drawbacks of the present analysis as compared to previous theoretical models. Sectorial expansion. morphogenesis. ornamentation, septal suture, coiled shell, gastropods, bivalues. ammonites.

Finite element analysis of a double membrane tube (DMS-tube) and its implication for gastropod shell morphology.

Molluscan shells, including those of Gastropoda, are formed by accretionary growth at the mantle edge. The mantle is a thin membrane of skirt-like shape, which extends minutely beyond the aperture, and its edge adds a shell increment to the aperture margin so that each increment copies a configuration of the mantle edge at that time. Thus, regulation of shell morphogeny is almost equivalent to the factors which control the mantle form at the moment of shell growth. Form of the mantle skirt is considered to be kept in a state of balance between the force of its internal stress and forces acting on it such as fluid pressure or muscle contraction. The expansion behavior of the mantle skirt has been numerically analyzed by using an elastic model (DMS-tube), which represents the fundamental structure of the mantle tissue as a double membrane structure with internal springs (DMS). Four characteristic expansion patterns of the DMS-tube have been detected: (1) general outward expansion; (2) developing a ridge-like fold on an initial longitudinal protrusion of the tube edge; (3) drastic shift of the expanded state from a uniformly curved to an elliptical shape in outline, owing to the existence of a fixed boundary condition on the tube wall; and (4) constricted protrusion on the open region of the shell wall surrounding the DMS-tube. These results have the potential for answering the following questions relating to the morphogenesis of gastropod shells. How does the mantle skirt usually make contact with the inner surface of the shell wall so as to ensure continuous accretion of shell materials to the aperture margin? What is the cause of spiral ridges? Why do open coiling or minimally overlapping shells have generally circular apertures, while shells with apertures overlapped by whorls have non-uniformly curved apertural lips? What is the cause of long closed spines and why do they always appear on spiral ridges?

Biological aspects of theoretical shell morphology

Savazzi, E. 1990 04 15: Biological aspects of theoretical shell morphology. Lethaia. Vol. 23, pp. 195–212. Oslo. ISSN 0024–1164 Among the available methods in theoretical shell morphology. moving-frame method, produce the broadest range of shell shapes and appear to emulate most closely the biological processes involved in shell morphogenesis and growth. In addition, moving-frame methods can easily be enhnneed in both respects by adding operations that are similar in nature to the original procedures. Improvements beyond this point. however. require a qualitative change in approach. The focus of attention must he transferred from the shell lo the soft parts involved in shell construction. This may be done by (1) regarding the soft parts a5 pneus. and (2) controlling their shape and metabolism through morphogenetic programme based on biochemical reactions. *Theoretical morphology. functional morphology, modelling. computer graphics, Mollusca. Gastropoda. Bivalvia. Brachiopoda.

A novel method for obtaining poliovirus 14 S pentamers from procapsids and their self-assembly into virus-like shells

Poliovirus procapsids, isolated and partially purified from infected HeLa cells, were found to dissociate into 14 S pentamers following freezing at −20° overnight. Unlike pentameric subunits isolated directly from virus-infected cells or those obtained by alkaline treatment of procapsids, the “freeze-dissociated” subunits self-assembled at room temperature into two kinds of empty capsids, one of which was similar to the shell of poliovirions as shown by its neutral p l, resistance to alkaline dissociation, and the presence of neutralization-related (N) epitopes. The other empty acidic p l and absence of N antigenic determinants. At 37°, the assembly reaction was significantly faster but only SAEC were formed. By following the assembly reaction by electron microscopy, intermediate structures were visualized; their relatively low amount at any given time was consistent with the previous hypothesis ( J. R. Putnak and B. A. Phillips (1981), J. Virol. 40, 173–183) that initiation is the rate-limiting step in the morphogenesis of empty shells. The relevance of these findings to the morphogenesis of picornaviruses, and polioviruses in particular, is discussed.

Post-larval development of the bivalves Nucula turgida, Venus striatula, Spisula subtruncata and S. elliptica (Mollusca: Bivalvia), (with reference to the late larva)

Detailed studies of post-larval shell, hinge and/or internal morphogenesis, from metamorphosis to the completion of development, are available for a very small number of infaunal bivalves (for review of studies see Webb (1984). This paper continues the description, using scanning electron microscopy (SEM), of the post-larval ontogeny of some common infaunal bivalves from north-west European communities and presents the development of Nucula turgida, Venus striatula, Spisula subtruncata and S. elliptica. The association between larval shell morphology and certain features of development in some protobranch bivalves is examined.

Skeletal morphogenesis in some living collosphaerid Radiolaria

Two major patterns of shell morphogenesis occurring in varying proportions among species were identified by examining skeletons from five species of living collosphaerid, colonial Radiolaria: Collosphaera huxleyi, Acrosphaera cyrtodon, Acrosphaera spinosa, Siphonosphaera tubulosa and Siphonosphaera socialis. Skeletons possessing large open-lattice structures characterized by ellipsoidal to polygonal pores separated by narrow bars are produced by repeated subdivision of large pores into smaller pores. A bridge-like bar grows across the pore and subdivides it into two or more smaller pores. In skeletons with small, nearly circular pores and occasionally elongated tubular rims, the pores appear to be developed by rim thickening. Silica is deposited at the perimeter of the pore, thus decreasing its diameter and increasing the bar width between pores. In some species exhibiting intermediate types of skeletal morphology, there appears to be varying amounts of both bridge growth and rim growth. These data are used to explore possible phylogenetic pathways for a variety of collosphaerid species and to elucidate the processes of skeletal deposition in Radiolaria.

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.