Embryonic development in the Patagonian red snail Odontocymbiola magellanica (Neogastropoda: Volutidae): Morphology and biochemistry

Embryo morphology, feeding mechanism and changes in composition of the egg capsule content during development (intracapsular fluids and embryos) were studied in Odontocymbiola magellanica from newly spawned egg capsules to the pre-hatching juvenile stage. Changes in embryo morphology and behavior are presented, based on observations and micrographs of living specimens and scanning electron microscopy. The arrangement of velar cilia and athrocytes and shell gland location and development differed markedly from other studied caenogastropods. Embryo ingestion of intracapsular fluid was promoted by velar ciliary currents at least from the early veliger stage, while feeding by grazing on the inner membranous layer of the egg capsule was rarely observed until juveniles were about to hatch. The main growth of embryos occurred during the veliger stages. A significant nutritional investment in egg capsules, as compared with other South American volutids was observed. Nutrition from proteins seemed to predominate at the expense of a high molecular weight fraction (>220 kDa). Calcium concentration in the intracapsular fluid remained constant during development, but notably, the total intracapsular content (i.e., the amount contained in both fluid and embryos) increased 3-fold, which may be explained by extraction from the egg capsule magnesium-rich calcite cover, or alternatively, by uptake of calcium from the surrounding sea water. Ammonia, a major end-product of nitrogen metabolism in marine invertebrates, was present in both embryos and intracapsular fluid, from which it may easily diffuse to the surrounding sea water through the egg capsule wall. Our results on embryo morphology, development and biochemical changes provide useful comparative data for evolutionary and developmental studies in the Volutidae as well as in other caenogastropods.     

Laboratory spawning of the purple snail Plicopurpura pansa (Gastropoda: Muricidae)

The spawning of the muricid gastropod Plicopurpura pansa in the laboratory at 22-23 degrees C is described. Females deposited 1-20 capsules daily for at least 20 weeks, and produced up to 150 capsules each per spawning season. During spawning, egg clusters were formed consisting of hundreds of capsules of different ages deposited by different females. Each egg capsule contained an average of 436 embryos (+/- s.d. 213.6, range: 95-1092, n=50). Embryos developed without nurse eggs. After six to eight weeks of intracapsular, lecithotrophic development, planktotrophic veligers hatched with two fully developed velar lobes.     

Embryonic development and reproductive seasonality of Buccinanops globulosus (Nassariidae) (Kiener, 1834) in Patagonia,Argentina

Buccinanops globulosus mated all year round, with higher frequency from May to September, prior to spawning months. Gravid females were found between October and March. Oviposition peaked during rising temperatures and longest daylength while hatching peaked with high water temperature and declining daylength. Gravid females measured between 20 and 41?mm in shell length. The spawn consisted on average of 31 egg capsules, each containing 1266 eggs. Embryos usually completed development within each egg capsule by ingesting small fragments of the uncleaved nurse eggs, which were not a limiting resource. Egg capsules with more than one embryo were not common; in those cases, the embryos had different sizes probably related to intracapsular competition for nutrients, and were on average smaller than solitary embryos in the other capsules. Embryos hatched as crawling juveniles with a mean hatchling shell length of ~3.4?mm. In a few cases, malformed embryos were found, but it was not a common phenomenon. The information recorded in this study, as the minimum reproductive size and spawning season, is valuable for fisheries management.     

Development and the influence of nurse egg allotment on hatching size in Searlesia dira (Reeve, 1846) (Prosobranchia : Buccinidae)

The reproductive biology of the intertidal prosobranch Searlesia dira (Reeve, 1846) was examined with special attention given to variability in the nurse egg to embryo ratio among capsules, among clutches and among geographically isolated populations. Embryos and nurse eggs were distributed among the capsules in a manner consistent with the hypothesis that nurse eggs were genetically predetermined, that each female had a genetically defined nurse egg to embryo ratio, and that each capsule represented a random sample of that ratio. The binomial distribution of embryos and nurse eggs among the capsules resulted in some capsules receiving many more embryos per nurse egg than others. The number of nurse eggs an embryo succeeded in eating was proportional to the number of capsule-mates sharing a capsule. Embryos eating more nurse eggs hatched out at a larger size. Differences in the nurse egg to embryo ratios among capsules in the same clutch were much larger than that of the mean ratios among clutches. Among-site differences in the mean nurse egg to embryo ratios suggest that selection pressure for different mean hatching sizes may have acted on the mean nurse egg to embryo ratios.In contrast to the predictions of optimal hatching size theory, hatching size varied widely within clutches as a consequence of differences in nurse egg to embryo ratios among capsules. This variance may be adaptive for species that lay their eggs months before juveniles emerge into an unpredictable environment, or simply be a consequence of an imperfect mechanism for increasing hatching size.     

Role of maternal provisioning in controlling interpopulation variation in hatching size in the marine snail Nucella ostrina

This study examined the role of maternal provisioning in controlling interpopulation variation in hatching size in nine isolated populations of the intertidal gastropod Nucella ostrina, in which development to the early juvenile stage takes place within an egg capsule. Variation among populations was almost entirely due to the ratio of nurse eggs to embryo, which explained 65% of the variation in hatching size. Egg size was not a significant predictor of hatching size. Differences among seven of these populations in the nurse egg/embryo ratio were entirely due to the number of nurse eggs allocated per capsule; these populations allocated different numbers of nurse eggs per capsule but allocated the same number of embryos. Intriguingly, the two most wave-sheltered populations allocated significantly more nurse eggs and more embryos to each capsule than did the seven other populations, but they maintained nurse egg/embryo ratios consistent with patterns observed in the other populations. Inter- and intrapopulation variation in hatching size appears to be controlled largely by different mechanisms: within-population variation being controlled mainly by differences in allocation of embryos per capsule, whereas most among-population variation being due to differences in allocation of nurse eggs per capsule.     

Early development of the limpet Siphonaria lessonii Blainville, 1827 in populations affected by different physical stressors

The limpet Siphonaria lessonii is very common along Atlantic Patagonian intertidal rocky shores. We studied the early intracapsular embryonic development of this limpet in detail in two populations in north Patagonia, with different environmental conditions (i.e. wave exposure, wind, temperature). Early development in both populations was achieved at controlled and equal conditions (13°C). The spawn consisted of a series of enchained egg capsules embedded in a jelly mass. The development from egg to hatching veliger took 9–11 days in embryos from both populations. The developmental process at both sites was identical, differing only in the embryos' sizes at each stage. Larger adult individuals producing larger embryos were registered at the sheltered site. The differences in sizes of adult and embryos of S. lessonii could be attributed to distinct environmental stressful conditions between sites.     

Embryonic development of the false limpet Siphonaria lateralis from Atlantic Patagonia

Siphonariids are pulmonate gastropods inhabiting rocky intertidal habitats, and many studies have focused on these false limpets around the world. In the southern South Atlantic, studies on reproduction and development in species of Siphonaria are scarce. We studied the embryonic development and egg masses of Siphonaria lateralis at its northernmost distribution in Atlantic Patagonia. In S. lateralis, as in most species of Siphonaria, individuals spawn benthic egg masses that strongly attach to intertidal rocky substrata. A single spherical egg that measures ~120 µm develops inside the egg capsule of S. lateralis. Considering the relatively small egg size, and reports from previous studies, the developmental modality of S. lateralis might be expected to include a planktotrophic larval phase. However, we found that hatchlings emerged as 1‐mm crawling juveniles, probably owing to the presence of intracapsular fluid, which may provide the energetic requirements for direct development. The embryonic size changed little from the egg to veliger stages, and then increased rapidly until the hatchling stage. We compared development in S. lateralis with development in the sympatric Siphonaria lessonii, in which egg size was reported to be ~80 µm and hatching occurs as planktotrophic veliger larvae. In these two species, spawn and early intracapsular developmental modes are remarkably different; these differences represent contrasting ways to survive in the harsh and physically stressful intertidal Patagonian coasts.     

Embryonic development of the sea butterfly Desmopterus papilio (Gastropoda: Thecosomata)

The embryonic development of the thecosome Desmopterus papilio is described for the first time. The mature individual produced a round-shaped egg mass containing ca. 200 fertilised eggs. First cleavage was observed 15 min after the release of the egg mass. Embryos showed typical molluscan spiral cleavage: macromeres produced the first and second quartets of micromeres in clockwise and counterclockwise directions, respectively. A trochophore larva hatched from the egg capsule 28 h after the release of the egg mass. Thereafter, the larva secreted a primary shell at the posterior part, developing into the veliger stage. These findings may be useful for future work on postembryonic development, especially on the loss of the veliger shell, in the genus Desmopterus which is the only group of thecosome species without a shell in the adult stage.     

Capsule walls as barriers to oxygen availability: Implications for the development of brooded embryos by the estuarine gastropod Crepipatella dilatata (Calyptraeidae)

Encapsulation of developing embryos imposes potential restrictions, because the capsule wall must allow for adequate inward diffusion of oxygen and for increased diffusion of oxygen as metabolic demand increases with continued development. Samples of egg capsules from the gastropod Crepipatella dilatata were used to document surface characteristics, composition of the different capsule wall layers, and alterations in wall thickness during development. The diffusion coefficient and capsule wall permeability were determined experimentally for capsules containing embryos at different developmental stages. We also determined oxygen consumption rates for various embryonic stages and for nurse eggs, which provide food for embryos during development. The capsule wall of C. dilatata possesses 2 differentiated layers: the external capsular wall (ECW) and the internal capsular wall (ICW). The ECW is compact and fibrous, features that remain invariable during development, and lacks surface features that might make some portions of the capsule wall more permeable to oxygen than others. On the other hand, the ICW is initially spongy and thick, but significantly decreases in thickness over time, particularly before the embryos begin feeding on nurse eggs. Although the capsule wall is a serious barrier to diffusion, permeability to oxygen increases over time by 112% due to the dramatic thinning of the inner capsule wall layer. Nurse eggs consume oxygen but at very low rates, supporting the idea that they correspond to living embryonic cells that have stopped their development. Respiration measurements indicated that embryos are initially supplied with enough oxygen within the egg capsules to carry out the activities characteristic of embryogenesis, even though the capsular walls show their maximum thickness and lowest permeability at this time. However, as the embryo develops its velum and becomes more active, capsule wall thickness decreases and capsule permeability to oxygen increases. Correspondingly, the oxygen demands of metamorphosed but still encapsulated specimens are approximately 135% higher than those of pre-metamorphosed sibling embryos.     

DNA-RNA hybridization studies of gene activity during the development of the gastropod, Acmaea scutum

DNA-RNA molecular hybridization experiments were performed to compare sequences of RNA that are present in the unfertilized egg, gastrula, trochophore, early veliger, mid-veliger, and adult with that population that is being synthesized by the midveliger. The conditions of annealing were designed to examine the more common RNA sequences that are complementary to the highly reiterated sequences of the genome. It was found that the RNA of the unfertilized egg competes extensively with RNA sequences that are being synthesized by this relatively late larval stage. These RNA sequences are present at a lower concentration in RNA preparations extracted from unfertilized eggs as compared to later stages. Autoradiographs of ³H-uridine labeled veligers indicate that the pulse-labeled RNA used in these experiments represents that synthesized by a wide variety of larval tissues. These results are discussed with respect to differences in RNA metabolism and determination between regulative and mosaic embryos.     

Embryonic rotational behaviour in the pond snail Lymnaea stagnalis: influences of environmental oxygen and development stage

Responses of freshwater organisms to environmental oxygen tensions (PO₂) have focused on adult (i.e. late developmental) stages, yet responses of embryonic stages to changes in environmental PO₂ must also have implications for organismal biology. Here we assess how the rotational behaviour of the freshwater snail Lymnaea stagnalis changes during development in response to conditions of hypoxia and hyperoxia. As rotation rate is linked to gas mixing in the fluid surrounding the embryo, we predicted that it would increase under hypoxic conditions but decrease under hyperoxia. Contrary to predictions, early, veliger stage embryos showed no change in their rotation rate under hyperoxia, and later, hippo stage embryos showed only a marginally significant increase in rotation under these conditions. Predictions for hypoxia were broadly supported, however, with both veliger and hippo stages showing a marked hypoxia-related increase in their rotation rates. There were also subtle differences between developmental stages, with hippos responding at PO₂s (50% air saturation) greater than those required to elicit a similar response in veligers (20% air saturation). Differences between developmental stages also occurred on return to normoxic conditions following hypoxia: rotation in veligers returned to pre-exposure levels, whereas there was a virtual cessation in embryos at the hippo stage, likely the result of overstimulation of oxygen sensors driving ciliary movement in later, more developed embryos. Together, these findings suggest that the spinning activity of L. stagnalis embryos varies depending on environmental PO₂s and developmental stage, increasing during hypoxia to mix capsular contents and maintain a diffusive gradient for oxygen entry into the capsule from the external environment (“stir-bar” theory of embryonic rotational behaviour).     

Reproduction and development in a vermetid gastropod, Vermetus triquetrus

Abstract. We report on a study of reproduction and development in the Mediterranean vermetid gastropod Vermetus triquetrus from the SE coast of Spain. It is a gonochoristic species. The egg capsules are attached to the inside of the shell, and females brood up to 22 capsules simultaneously (more often 4–10). The capsules hold 10–61 eggs or embryos; the uncleaved eggs are yolk-rich, with a mean diameter of 377.3 μm. A distinct polar lobe occurs during the first cleavage, and blastomere D has discernible qualities after the 4-cell stage. The formation of the mesentoblast 4d occurs at the transition from the 24-cell stage to the 25-cell stage. Gastrulation begins after the 36-cell stage. Internal yolk is the major source of nutrition for the encapsulated embryos, but some nurse eggs (∼ 12%) and some sibling larvae are also ingested by the developing embryos. Hatching occurs during the swimming/crawling pediveliger stage, and metamorphosis is completed outside the capsules soon after hatching. Hence, larval development in Vermetus triquetrus is lecithotrophic intracapsular, with a short free-swimming/crawling phase.     

Larval development and metamorphosis in the marine pulmonate Amphibola crenata (Mollusca: Pulmonata)

The development of the free-swimming veliger of Amphibola is followed from hatching to settlement, and the larval structures compared with those of post-metamorphic juveniles and adult snails. Observations of living specimens and light-microscope sections were combined with scanning electron microscopy to build up a composite picture of veliger structure.
Four stages in the development of veligers are recognized, each being characterized by the appearance of organ systems such as the mantle cavity, larval heart, adult heart and kidney, and larval pallial gland. At or after metamorphosis, the larval systems (heart, kidney and pallial gland) disappear, and the developing adult organs move to the positions characteristic of adult snails.
Organogenesis in Amphibola veligers is compared with that of prosobranch and opisthobranch larvae, and with that of pulmonate larvae with direct development. The closest similarity is seen to be with opisthobranch veligers.     

EARLY STAGES OF THE ENCAPSULATED DEVELOPMENT OF NUCELLA LAPILLUS (LINNAEUS) (GASTROPODA, MURICIDAE)

The intertidal muricid gastropod Nucella lapillus (Linnaeus)develops entirely within an egg capsule up to the juvenile stage.This study investigates how the embryos have adapted to theabundance of their own yolk (protolecith) and extraembryonicnutrients (nurse eggs, capsule fluid) during five stages ofearly organogenesis The pretorsional preveliger uses protolecith and albumen asnutritive resources. The main portion of the protolecith isstored in the large unequal macro-mere 4D, which is interpretedto be an adaptation to the large content of its own yolk andpersists beyond the ingestion stage. The transitory storageof protolecith makes the predominant resorption of the nutritiveeggs possible. The stomodaeum develops early as an ectodermalinvagination and opens into an anterior buccal part and a posterioroesophageal part. The radular sac is of early pretorsional origin.Some prospective endodermal structures (midgut and hindgut)first become apparent by their histological differentiation During ingestion the differentiation of midgut and cephalopodiumis arrested. The extremely thin epithelium of the midgut surroundsthe swallowed nurse eggs The last stage, an early veliger, has developed all essentialorgans as rudiments, except the coelomic derivates and the pallia]organs. The hindgut opens by a proctodaeal invagination (anus).The embryo undergoes further torsional displacement (Received 20 August 1987;     

Report of a cohesive gelatinous egg mass produced by a tropical marine bivalve

Abstract. Gelatinous egg masses are common in a number of animal phyla. However, they are virtually unknown in marine bivalves, with structures that could be thought of as gelatinous egg masses being reported for only five species. We describe the gelatinous egg mass and intracapsular development in the tropical lucinid Phacoides pectinatus. The embryos developed within individual capsules embedded in a large flimsy, spherical mass. Swimming veligers hatch at 198 μm shell length. They did not feed, settled within several days of hatching, and metamorphosis was completed within 2 weeks of hatching. Gelatinous egg masses might be detected in members of more lucinid species if studies of development included field or in vivo observations of reproduction in addition to producing embryos by stripping the gonads.     

Energy source utilization by embryos and larvae of the muricid snail Chorus giganteus (Lesson, 1829)

The muricacean snail Chorus giganteus presents intracapsular development and the occurrence of nurse eggs that are ingested by the early encapsulated embryos indicate both that these snails develop through a lecitotrophic type of development and that reserves would be sufficient to support settlement and metamorphosis. In order to get more information about the use of energy resources, the dynamics of biochemical components throughout development at three temperatures (9, 12 and 15 °C) and the energetic cost of free-swimming life and metamorphosis are described. The uptake of ³H-alanine, as representative of dissolved organic matter, by embryo and larval stages is also investigated. While protein levels increased at all temperature conditions after ingestion of nurse eggs, lipids only increased when embryo and larvae were reared at 15 °C, and no change in carbohydrate levels was detected at any of the temperatures. The RNA/DNA indexes showed no significant differences with temperature at any stage of development but decreased along with the development of individuals. After hatching, organic matter and energy content of juveniles steadily decreased. Individuals at any of the developmental stage showed to be able to uptake alanine from seawater; the aminoacid uptake capacity increased along with intracapsular development. Uptake of alanine showed to be an active process and to follow Michaelis-Menten kinetics. This would be the first report about dissolved organic matter uptake by encapsulated development stages of any marine invertebrate species and let conclude that these larvae have the ability to obtain exogenous food in a dissolved form and to incorporate it into metabolizable compounds.     

Spring diet of common eiders (Somateria mollissima) in Breiðafjörður, West Iceland, indicates non-bivalve preferences

Breiðafjörður is an important molting, breeding, and wintering area for about 25 % of the Icelandic common eider (Somateria mollissima) population. However, feeding habits of eiders in this area have not been investigated until now. Prey selection was analyzed from 192 stomach samples (esophagus and proventriculus) collected in spring 2007–2010. Thirty-five prey species were identified; the highest percentage occurrences were of gastropods (79 %), chitons (polyplacophorans) (58 %), crustaceans (43 %), bivalves (26 %), and echinoderms (8 %). The most common food species was the mottled red chiton Tonicella marmorea (58 %), followed by the common whelk Buccinum undatum (40 %), the spider crab Hyas arenarius (39 %), and the chink shell Lacuna vincta (35 %). The majority of the food items was of small size and consumed in high quantity. The chitons and mussels were of similar average sizes (11.7 and 13.4 mm, respectively), which might suggest that prey size could be as important as species in food selection. There were some inter-annual differences in dominant prey classes between years. For example T. marmorea was found in 60–70 % of birds in the years 2007 and 2009 but only in 30 % of the birds in the other years investigated. Diets of males and females were equally diverse and similar when all months and years were pooled. Prey selection was highly variable but most individuals focused on few or a single species in the hours prior to collection. Results indicate that the most common prey species for common eiders is a chiton and not blue mussels as reported elsewhere.     

Transmission of Nephridial Bacteria of the Earthworm Eisenia fetida

The lumbricid earthworms (annelid family Lumbricidae) harbor gram-negative bacteria in their excretory organs, the nephridia. Comparative 16S rRNA gene sequencing of bacteria associated with the nephridia of several earthworm species has shown that each species of worm harbors a distinct bacterial species and that the bacteria from different species form a monophyletic cluster within the genus Acidovorax, suggesting that there is a specific association resulting from radiation from a common bacterial ancestor. Previous microscopy and culture studies revealed the presence of bacteria within the egg capsules and on the surface of embryos but did not demonstrate that the bacteria within the egg capsule were the same bacteria that colonized the nephridia. We present evidence, based on curing experiments, in situ hybridizations with Acidovorax-specific probes, and 16S rRNA gene sequence analysis, that the egg capsules contain high numbers of the bacterial symbiont and that juveniles are colonized during development within the egg capsule. Studies exposing aposymbiotic hatchlings to colonized adults and their bedding material suggested that juvenile earthworms do not readily acquire bacteria from the soil after hatching but must be colonized during development by bacteria deposited in the egg capsule. Whether this is due to the developmental stage of the host or the physiological state of the symbiont remains to be investigated.     

Effects of temperature, salinity, and air exposure on development of the estuarine pulmonate gastropod Amphibola crenata

The primitive pulmonate snail Amphibola crenata embeds embryos within a smooth mud collar on exposed estuarine mudflats in New Zealand. Development through hatching of free-swimming veliger larvae was monitored at 15 salinity and temperature combinations covering the range of 2-30 ppt salinity and 15-25 °C. The effect of exposure to air on developmental rate was also assessed. There were approximately 18,000 embryos in each egg collar. The total number of veligers released from standard-sized egg collar fragments varied with both temperature and salinity: embryonic survival was generally higher at 15 and 20 °C than at 25 °C; moreover, survival was generally highest at intermediate salinities, and greatly reduced at 2 ppt salinity regardless of temperature. Even at 2 ppt salinity, however, about one-third of embryos were able to develop successfully to hatching. Embryonic tolerance to low salinity was apparently a property of the embryos themselves, or of the surrounding egg capsules; there was no indication that the egg collars protected embryos from exposure to environmental stress. Mean hatching times ranged between 7 and 22 days, with reduced developmental rates both at lower temperature and lower salinity. At each salinity tested, developmental rate to hatching was similar at 20 and 25 °C. At 15 °C, time to hatching was approximately double that recorded at the two higher exposure temperatures. Exposing the egg collars to air for 6-9 h each day at 20 °C (20 ppt salinity) accelerated hatching by about 24 h, suggesting that developmental rate in this species is limited by the rates at which oxygen or wastes can diffuse into and from intact collars, respectively. Similarly, veligers from egg capsules that were artificially separated from egg collars at 20 °C developed faster than those within intact egg collars. The remarkable ability of embryos of A. crenata to hatch over such a wide range of temperatures and salinities, and to tolerate a considerable degree of exposure to air, explains the successful colonization of this species far up into New Zealand estuaries.