Outer Calcareous Layer Research Articles

Novel type of egg-clustering in threadsnakes (Serpentes: Leptotyphlopidae)

Abstract Snakes lay their eggs in clutches of different size, which are usually attached to each other forming a cluster. Egg-clustering is a widespread phenomenon across alethinophidian snakes, mostly recorded in Pythonoidea and caenophidian clades. Here we report a new type of egg-clustering for threadsnakes (Leptotyphlopidae) that departs from the alethinophidian type. We found that females of Epictia australis and Leptotyphlops sylvicolus lay their eggs connected to each other through a filament, and we dubbed it ‘string-egg clustering’. The histomorphology of the filament linking the eggs in E. australis showed an outer calcareous layer underlain by a thick layer of collagen fibers, demonstrating that it is an integral part of the eggshell formed during its deposition process in the oviduct. String egg-clustering seems to be present only among species belonging to both subfamilies of threadsnakes, Epictinae and Leptotyphlopinae. Egg-clustering in alethinophidians has been demonstrated to have several advantages for embryo development and post-hatching survival, including fixing the position of the embryo within the egg, protection against predators, and embryo-to-embryo communication. The presence of a filament connecting the eggs in leptotyphlopid species might be relevant for maintaining the position of the embryo in the egg, to avoid the dispersion of the egg in the nesting site, and potentially for the transmission of physical cues. Thus, we hypothesize that the string-egg clustering constitutes an advantageous reproductive trait among threadsnakes.

Facultative mobilization of eggshell calcium promotes embryonic growth in an oviparous snake.

The mineralized eggshell of Reptilia was a major innovation in the evolution of the amniotic egg. Inorganic components strengthen the eggshell and are a potential source of nutrients to developing embryos. Embryos of oviparous reptiles do extract calcium from eggshells but vary interspecifically in exploitation of this resource. The pattern of embryonic calcium nutrition of the corn snake, Pantherophis guttatus, is similar to a diversity of squamate species: embryos obtain most calcium from yolk, yet also mobilize calcium from the eggshell. We tested the hypothesis that embryonic development is not dependent on eggshell calcium by manipulating calcium availability. We peeled away the outer calcareous layer of the eggshell of recently oviposited eggs; control eggs were left intact. Eggs were sampled periodically and calcium content of egg compartments (embryo, yolk, eggshell) was measured. We also analyzed skeletal development and size of hatchlings. There was no difference in survivorship or length of incubation between treatments. However, hatchlings from intact eggs contained more calcium and were larger in mass and length than siblings from peeled eggs. There were no observable differences in ossification but hatchlings from intact eggs had larger skeletal elements (skull, vertebrae). Our results indicate that mobilization of eggshell calcium is not a requirement for embryonic development of P. guttatus and that embryos augment yolk calcium by extracting calcium from the eggshell. This pattern of embryonic calcium nutrition would favor embryos with a greater capacity to mobilize calcium from the eggshell by promoting growth and thereby potentially enhancing hatchling fitness.

Drilling predation on neritid egg capsules by the muricid snail Reishia clavigera

The egg capsules of neritid snails (Gastropoda: Neritimorpha) are made of a tough inner organic layer and an outer calcareous layer for further reinforcement. Such hard capsules are less susceptible to mechanical damage compared with soft or thin capsules of other gastropods, and there have been only a few reports of predation on neritid eggs. Here, we describe drilling predation on the reinforced egg capsule of Nerita japonica by Reishia clavigera (Caenogastropoda: Muricidae) on a high intertidal rocky shore in central Japan. The muricid makes a small, elliptical drill hole in the capsule lid by the use of both an accessory boring organ (ABO) and a radula, as it does in mollusc and barnacle shells. The etching around the hole by the acid secretion from the ABO, which can be observed under a dissecting microscope and by scanning electron microscopy, should provide an effective way to identify muricid predation on neritid eggs, probably not only by R. clavigera but also by other species in the warm temperate to tropical regions all over the world. Reishia clavigera made drill holes in c. 14% of the capsules, making it possibly the main cause of mortality for neritid eggs at the study site. However, this mortality rate is lower than those previously reported for caenogastropod eggs with softer capsules. All penetrated capsules of N. japonica were white (rather than brownish) and newly laid, suggesting that their acid-resistant organic layer had yet to harden at the time of radular rasping. The thick organic layer and calcareous coating are an effective armour, not only against the usual type of grazing but also against more sophisticated predation involving the chemical and mechanical boring of Muricidae.

Microstructure and mineralogy of the outer calcareous layer in the lower jaws of Cretaceous Tetragonitoidea and Desmoceratoidea (Ammonoidea)

Tanabe, K., Landman, N.H. & Kruta, I. 2011: Microstructure and mineralogy of the outer calcareous layer in the lower jaws of Cretaceous Tetragonitoidea and Desmoceratoidea (Ammonoidea). Lethaia, Vol. 45, pp. 191–199. Based on the differences in their relative size, overall shape, structure and the degree of development of an outer calcified covering, lower jaws of the Ammonoidea have been classified into four morphotypes: normal, anaptychus, aptychus and rhynchaptychus types. However, detailed microstructural and mineralogical comparison of these morphotypes has not yet been addressed. This article documents the results of SEM and XRD observations of the lower jaws of three Late Cretaceous ammonoid species belonging to the Tetragonitoidea (Anagaudryceras limatum) and Desmoceratoidea (Pachydiscus kamishakensis and Damesites aff. sugata), based on excellent material preserved in situ within the body chamber, and retaining an aragonitic shell wall. The lower jaws of the three species are assigned to an intermediate form between anaptychus and aptychus types for the first two species and the rhynchaptychus type for the third species. Their black, presumably originally chitinous outer lamella is wholly covered with a calcareous layer. The calcareous layer is composed of aragonite in D. aff. sugata and A. limatum, and calcite in P. kamishakensis. The microstructure of the outer calcareous layer differs among the three species, i.e. granular in A. limatum, spherulitic prismatic in D. sugata, and prismatic in P. kamishakensis, all of which can be distinguished from the lamellar and spongy structure of the outer-paired calcitic plates of the typical aptychus-type lower jaws in some Jurassic and Cretaceous Ammonitina and Ancyloceratina. Our study suggests that most Jurassic and Cretaceous ammonoids possessed an outer calcareous layer in their lower jaws, although its mineralogy, microstructure and relative thickness vary among different taxa. □Ammonoidea, Cretaceous, Desmoceratoidea, lower jaw, microstructure, Tetragonitoidea.

Analysis of Elemental Composition of the Eggshell before and after Incubation in the Loggerhead Turtle (Caretta caretta) in Oman

To date, there are limited studies on loggerhead turtle (Caretta caretta) eggshell ultrastructure and its elemental composition. Eggs were collected from turtle nests immediately after oviposition and post hatching. Three eggshell layers were recognized. The outer calcareous layer consists of loose nodular units of different shapes and sizes with loose attachment between the units, resulting in numerous spaces and openings. Each unit consists of CaCO3 crystals in aragonite (99%) and calcite (1%). The middle layer has several strata with numerous openings connecting the calcareous and the inner shell membrane. Crystallites of the middle layer are a mix of amorphous material with aragonite (62%) and calcite (38%). The inner shell membrane has numerous reticular fibers mixed predominantly with halite (NaCl) and small amounts of sylvite. Thermogravimetry analysis of the calcareous showed a low exothermic peak at 425°C, which corresponds to a transitional phase from aragonite to calcite. A high endothermic peak at 814°C corresponds to decomposition of calcite CaCO3 to CaO and CO2. Electron diffraction confirmed the presence of NaCl halite crystal. A significant difference was found in the percentage of elements and crystal configurations in the three layers. This study has value in assessing the emergence success in this endangered species.

Chemical Composition and Structure of the Eggshell of Three Oviparous Lizards

We investigated the structure of the eggshells of the oviparous scincid lizards, Lampropholis guichenoti and L. delicata, and the agamid Physignathus lesueurii. The eggshells of all three species consisted of an outer calcareous layer, a fibrous shell membrane, and an inner boundary layer. The eggshells of P. lesueurii had an additional amorphous layer between the calcareous and fibrous layers. The calcareous layer of all shells was relatively thin and contained calcium carbonate in the form of calcite, typical of oviparous squamates. The multilayered fibrous shell membrane constituted the majority of shell thickness. The calcareous layer contained the majority of inorganic ions, with calcium and magnesium being present in detectable quantities. Calcium carbonate crystals were also found on the inner boundary layer of the P. lesueurii shells. This phenomenon has only been described for one other species, the Tuatara.

Ammonite jaw apparatuses from the Sinemurian (Lower Jurassic) of Dorset and their taphonomic relevance

The occurrence of ammonite jaw apparatuses in situ within concretions from the Sinemurian (Lower Jurassic) of Black Ven Cliff, Charmouth, Dorset, provides evidence of burial of the ammonites with soft parts intact and this is of importance in considering the origin of the concretions. The lower jaws (anaptychi) of arietitid and eoderoceratid ammonites are preserved and three examples of upper jaws are recorded in the species Asteroceras stellare. Although usually accepted as being entirely of organic composition, the anaptychi of A. stellare have an outer calcareous layer.

Eggshell formation during prolonged gravidity of the tuatara Sphenodon punctatus.

Scanning electron microscopy (SEM) was used to examine the process of shell formation in tuatara. Tuatara carry eggs in the oviducts for ∼ 7-8 mo before nesting, a period of gravidity more than three times as long as in any other oviparous reptile. Our aim was to determine whether shell formation occurred rapidly after ovulation, or whether it occurred gradually throughout gravidity. Eggs were obtained from females in early gravidity (May, ∼ 1 mo after ovulation), midgravidity (August and September, 4-5 mo after ovulation), and late gravidity, immediately prior to nesting (December, 8 mo after ovulation). The shell membrane (fibrous layer) was well formed by May, but calcification of the outer surface had only just begun. Vertical columns of calcium carbonate were embedded in the shell membrane and appeared to erupt through the outer surface between early and midgravidity. Changes in the appearance of the outer calcareous layer were evident as gravidity progressed. In all shells, calcium carbonate was present as calcite. The appearance of the inner boundary (innermost layer of eggshell) was variable; some shells had a smooth and amorphous inner boundary as previously reported for tuatara and other reptiles, whereas other shells had an inner boundary composed of small spherical granules on the inner surface of which small calcareous spicules were scattered. A previously published model of the process of shell formation in tuatara eggshells is refined in light of our observations. We interpret the ability of female tuatara to shell their eggs gradually during winter as further evidence of their unusual physiological tolerance of cold conditions. © 1996 Wiley-Liss, Inc.

THE MANTLE AND SHELL OF SOLEMYA PARKINSONI (PROTOBRANCHIA: BIVALVIA)

The shell of Solemya exhibits considerable flexibility which is further enhanced by the marked extension of the periostracum beyond the calcareous portions of the valves. This fcature, more than any other, has made possible the habit, unique among bivalves, of burrowing deep within the substrate without direct contact with the water above. The inner calcareous layer of tho valves is restricted to a small area near the umbones while the outer calcareous layer is thin and contains a high proportion of organic material. The shell conchiolin consists mainly of protein, varying in composition, but much of it strengthcned by quinone‐tanning, and in ccrtain regions probably by the presence of appreciable quantities of chitin. The ligament, although superficially resembling an amphidetic structure, is opisthodetic, the extcnsion anterior to the umbones consisting of anterior outer layer only.The mantle is characterized by an extension of the outer fold of the mantle margin which has effected equally both the inner and outer surfaces of this fold. The secretory epithelium and the modified pallial musculature, contraction of which results in the intucking and plaiting of the periostracum, is dcscribed. Simple tubular oil glands open at the mantlo margin and are responsible for the water‐repellent nature of the periostracum.The form of the mantlelshell and that of the enclosed body are discussed and compared with those of other bivalves in which elongation of the mantle/shell is achieved in a different way. It is concluded that the mantlelshell of Solemya is of little value in determining its relationships, and that the greatly elongatod ligament, the edentulous hinge and the flexible shell are all adaptations to a specialized mode of life.

Observations on the Mantle of the Lamellibranchia

ABSTRACT The variation in histology between the epithelial regions of the mantle in Anodonta cygnea concerned with the secretion of the different layers of the shell has been investigated. The epithelia on the outer surface of the outer mantle fold which secrete the outer layer of the ligament and the corresponding outer calcareous layer of the valves are basically alike in structure. They are also comparable in appearance with the epithelium on the inner surface of the outer mantle fold which secretes the perio- stracum and with that of the fused outer folds responsible for the formation of the fusion layer of the ligament. All these epithelial regions can readily be distinguished histologically from the epithelia of the general outer mantle surface and of the mantle isthmus which produce the inner layers of the valves and ligament respectively. The histological differentiation of the mantle epithelium in Anodonta is compared with that of Mytilus edulis and Ostrea edulis. The degree of zonation of the epithelium can be correlated with the extent to which the shell layers differ in composition from one another. It is suggested that the variation in histological appearance between epithelia from different areas of the mantle is partly determined by the relative amounts of non-calcareous material (conchiolin) which these epithelia produce and by the rate of their secretory activity. The different epithelial regions of the mantle in Anodonta and other lamellibranchs vary appreciably in their reactions to histochemical tests for alkaline phosphatase, ribonucleic acids, and glycogen. In Anodonta, the epithelial cells of the outer mantle fold differ markedly from those which secrete the inner layers of the shell in that they exhibit high alkaline phosphatase activity and appear to be rich in cytoplasmic ribonucleic acids. In contrast, the epithelium of the general outer surface of the mantle is distinguished by a high content of glycogen, a condition which also occurs in many other bivalves. It is interesting to note that alkaline phosphatase can be demonstrated in epithelia which secrete non-calcareous regions of the shell. In all the lamellibranchs investigated, ribonucleic acids can be detected in relatively higher concentration in epithelial cells concerned principally with the secretion of conchiolin.

Form and habit inPinna carneaGmelin

Form and habit in<i>Pinna carnea</i>Gmelin