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Regeneration of the calcareous rigiclaudent operculum following severe, non-lethal, predatory attacks is described in two specimens of the characteristic Silurian gastropod Oriostoma from the English Midlands. This is the first record of the regeneration of opercula in Palaeozoic gastropods and of opercula conjoined with shells that have been repaired after significant, failed, durophagous attacks. In one specimen, a series of repaired injuries culminates in a repaired aperture closed by the operculum. In the second specimen, new shell growth has failed to recover the full extent of the original broken whorl, and the new aperture and operculum, though well developed, are smaller than the originals. Both opercula are unusually thin centrally when compared to other, strongly domed, Oriostoma opercula.

The recent reexamination of a tooth-whorl fossil of Helicoprion containing intact jaws shows that the symphyseal tooth-whorl occupies the entire length of Meckel's cartilage. Here, we use the morphology of the jaws and tooth-whorl to reconstruct the jaw musculature and develop a biomechanical model of the feeding mechanism in these early Permian predators. The jaw muscles may have generated large bite-forces; however, the mechanics of the jaws and whorl suggest that Helicoprion was better equipped for feeding on soft-bodied prey. Hard shelled prey would tend to slip anteriorly from the closing jaws due to the curvature of the tooth-whorl, lack of cuspate teeth on the palatoquadrate (PQ), and resistance of the prey. When feeding on soft-bodied prey, deformation of the prey traps prey tissue between the two halves of the PQ and the whorl. The curvature of the tooth-whorl and position of the exposed teeth relative to the jaw joint results in multiple tooth functions from anterior to posterior tooth that aid in feeding on soft-bodied prey. Posterior teeth cut and push prey deeper into the oral cavity, while middle teeth pierce and cut, and anterior teeth hook and drag more of the prey into the mouth. Furthermore, the anterior-posterior edges of the teeth facilitate prey cutting with jaw closure and jaw depression. The paths traveled by each tooth during jaw depression are reminiscent of curved pathways used with slashing weaponry such as swords and knifes. Thus, the jaws and tooth-whorl may have formed a multifunctional tool for capturing, processing, and transporting prey by cyclic opening and closing of the lower jaw in a sawing fashion.

During the Devonian Nekton Revolution, ammonoids show a progressive coiling of their shell just like many other pelagic mollusk groups. These now extinct, externally shelled cephalopods derived from bactritoid cephalopods with a straight shell in the Early Devonian. During the Devonian, evolutionary trends toward tighter coiling and a size reduction occurred in ammonoid embryonic shells. In at least three lineages, descendants with a closed umbilicus evolved convergently from forms with an opening in the first whorl (umbilical window). Other lineages having representatives with open umbilici became extinct around important Devonian events whereas only those with more tightly coiled embryonic shells survived. This change was accompanied by an evolutionary trend in shape of the initial chamber, but no clear trend in its size. The fact that several ammonoid lineages independently reduced and closed the umbilical window more or less synchronously indicates that common driving factors were involved. A trend in size decrease of the embryos as well as the concurrent increase in adult size in some lineages likely reflects a fundamental change in reproductive strategies toward a higher fecundity early in the evolutionary history of ammonoids. This might have played an important role in their subsequent success as well as in their demise.

A new species of giant fossil gastropod belonging to the genus Campanile, Campanile trevorjacksoni sp. nov., is described from the Lower Eocene Stettin Formation of the Yellow Limestone Group of Jamaica. Over 180 years ago, internal moulds of these giant gastropods were first reported from the Eocene of Jamaica and referred to as Cerithium; it is only with the discovery of an external mould of the shell spire that it can now be removed from open nomenclature. The ornate shell of C. trevorjacksoni has flat-sided to slightly rounded whorls; straight, impressed sutures; seven beaded, spiral cords per whorl and a nodose subsutural ridge in the more adapertural part of the shell. This sculpture differentiates C. trevorjacksoni from other Paleogene Campanile species. In 1827, de la Beche included C. trevorjacksoni (as Cerithium) in a list of over 20 taxa with which he correlated his white limestone formation (including the Yellow Limestone Group of modern use) with the (Eocene) Calcaire grossier of the Paris Basin. These specimens are lost, but re-examination of de la Beche's list suggests his identifications were mostly reasonable. Copyright © 2008 John Wiley & Sons, Ltd.

Based on the study of Early Paleozoic protoconchs, we (Nutzel et al. 2006) concluded that planktotrophic mollusc larvae are unknown from the Cambrian but became common in the Ordovician. Therefore, we assumed that planktotrophy itself evolved at the Cambrian/Ordovician transition and that it is unlikely that planktotrophy represents the original state in Metazoa. This is in agreement with other authors who followed different lines of evidence (see Nutzel et al. 2006). Freeman and Lundelius (FL Riedel 2000). However, such gastropods are known from the Cretaceous onwards only. Scissurellids and some other Vetigastropoda represent another important exception. They are nonplanktotrophic (as all vetigastropods) but have a small initial shell (scissurellids are known from the Triassic onwards). However, all these exceptions do not change the general picture that at a shell length of about 100mm, most planktotrophic molluscs are smaller than most nonplanktotrophic molluscs. Even in recent gastropods, it is commonly hard or impossible to determine the boundary between embryonic shell (protoconch I) and larval shell (protoconch II) and it becomes even more difficult in fossil material that is almost always recrystallized so that fine structures are obscured. Generally, protoconch preservation is rare in the Paleozoic. Most Late Paleozoic to extant gastropods have a tightly coiled initial whorl so that it is possible to measure the diameter of the first whorl if it is preserved. Most planktotrophic gastropods hatch with about one whorl (Figs. 1A and 2J) (e.g., Bandel 1975) and therefore the diameter of the initial whorl can be used to infer the approximate size of the hatchling even if the transition from protoconch I to II is not visible (Nutzel 1998). The oldest gastropods with well-preserved larval shells have been EVOLUTION & DEVELOPMENT 9:4, 313 –318 (2007)

Sediments of palaeolakes located in eastern Poland represent the Holsteinian (Mazovian) Interglacial, which corresponds to the Marine Isotope Stage 11 (MIS 11). Some of these sediments are characterized by an extremely rich occurrence of mollusc shells. A total of 1795 specimens of the snail Viviparus diluvianus were measured from 5 samples collected from a succession of lake deposits at Ortel Krolewski. The sample from the lowermost part of the succession (2.5 m) represents the Picea-Alnus pollen zone of the Holsteinian Interglacial. Samples from 2.0, 1.5, 1.0m are related to the Taxus Zone. Samples collected from the uppermost part of the succession (0.5 m) correspond to the Pinus Zone representing the so-called intra-interglacial cooling. The population of V. diluvianus displays variability correlated with climatic changes. The population from the Taxus Zone is characterized by a higher content of mature forms compared to the earlier population from the Picea-Alnus Zone. Because the mature individuals are slimmer than the juvenile forms, their last whorl is relatively lower and the aperture relatively smaller. In populations from the Taxus Zone the mean slimness of the shell therefore increases, followed by a decrease in the mean relative height of the last whorl and the mean relative aperture height.

The recently proposed subclass Euomphalomorpha Bandel and Frýda, 1998 was primarily based on an openly coiled, planispiral initial whorl. Here, the protoconch of Carboniferous euomphalids is described and figured in detail previously unknown. This protoconch comprises distinctly less than one planispiral whorl with an abrupt transition to the telecoconch. It is umbilicate or openly coiled. Umbilicate or bilaterally symmetrical protoconchs are still present in Recent species of the Cocculiniformia, the Neomphalidae and the Docoglossa. A previously suggested close phylogenetic relationship between the euomphalids and primitive gastropod limpets is therefore corroborated by the protoconch morphology. The fact that several Palaeozoic gastropods, unlike most modern gastropods, have an openly coiled initial whorl is highly remarkable, but the meaning of this feature for the phylogeny and the systematics of the Gastropoda is not yet clear.

Gastropod apertures reflect expanded states of their mantle edge under variable boundary conditions. The apertures are divided into two groups: apertures without distinct overlap zones (e.g., whorl overlap) and those with overlap zones. Each group follows a unique morphological rule. Apertures without overlap zones are generally circular in outline. Apertures with overlap zones are either elongated perpendicularly to the overlap zone or inflated abapically. Moreover, the latter abapically inflated apertures are generally accompanied by a straight section anterior to the overlap zone along the columellar axis (columellar part). Numerical analysis of an elastic double membrane tube whose main frame simulates the gastropod mantle indicates that these morphological rules are the products of mantle edge expansion under the condition that the head-foot mass presses against the mantle edge in both the overlap zone and the columellar part. The mantle edge in these two zones is thus in a completely or partly fixed boundary condition at the moment of shell growth. The rest of the mantle edge is free to expand either symmetrically or asymmetrically. It is hypothesized that the head-foot mass is a driving force for regulating the pattern of shell coiling and apertural shape.

Melanoides tuberculata in the Kuala Lumpur area of Malaysia were found to be entirely female, reproducing parthenogenetically. The reproductive system is extremely simple in structure and histology, lacking all the glandular developments common in most mesogastropods. Eggs pass into a cephalic brood-pouch where they develop to juveniles of 5–6 shell whorls before emergence. Numbers of developing young in the brood-pouches increased with shell height of the parents except for a decline in the few very largest snails. The highest brood-pouch count was 265, but average counts were much lower. 85 % of developing young in the brood-pouches were very early stages from eggs to embryos of one whorl only, perhaps implying that many eggs fail to develop successfully to young snails. Three localities studied yielded consistently different brood-pouch counts, implying variation in fecundity. Juveniles emerge from the brood-pouch most commonly between nightfall and midnight and normal emergence seems to require diurnal alternation of light and dark. In continuous darkness, brood-pouch counts increased markedly, perhaps as a result of greater activity and feeding during darkness. Several features of the reproductive biology suggest that Melanoides might become a useful experimental animal in freshwater studies.

In the column of hydra, tissues continually move away from a region located just underthe whorl of tentacles. Above this subtentacular region, tissues proceed into the hypostome and tentacles; below it tissues pass into the buds or continue down the stalk. These movements represent a steady state pattern of tissue renewal in which column growth is balanced by tissue loss at the body extremities. But the existence of a subtentacular zone in which tissue appears stationary does not necessarily indicate that growth is restrictedto this region, as is commonly stated. The body column of hydra can be viewed as an expanding cylinder whose elongation is balanced by tissue loss at the two ends. In such a body there must be one region from whichtissue appears to emanate, regardless of how growth is distributed along the cylinder. Only the rates at which tissues move will be characteristic of the underlying growthpattern. In Hydra littoralis, the measured rates of tissue movement down the gastric column are consistent with the distributions of mitotic figures, which indicate that growth is spread out along the column.

On the morphological evidence of three specimens Pelagohydra mirabilis Dendy is a floating tubularian hydroid of the subfamily Pelagohydrinae; its regional morphology is interpreted as homologous with the aboral and oral regions of the hydranths of genera such as Tubularia and Corymorpha, rather than with the hydrocaulus; the development of the aboral region into a fluid-filled float has been brought about by the enormous development of the diaphragm and its parenchymatous cushion, a process resulting also in the scattering of the aboral whorl of tentacles and the blastostyles to positions all over the float; buoyancy and movement of the hydroid is probably attained through density changes in the coelenteric fluid in the float.