Larval Shell Research Articles

Can bivalve veligers escape feeding currents of adult bivalves?

While the stock of introduced Pacific oysters ( Crassostrea gigas) increased in the Oosterschelde estuary (SW Netherlands), so did the filtration pressure of all bivalve species together. In the same period, stocks of native bivalves declined slightly. The expansion of Pacific oysters in Dutch estuaries might be partially due to better abilities of their larvae to avoid or escape filtration, compared to larvae of native bivalves. In this context, escape and swimming abilities of Pacific oyster larvae and the larvae of the native blue mussel ( Mytilus edulis) were compared. Swimming behaviour of C. gigas larvae and larvae of M. edulis was recorded in still water and in a suction current mimicking a bivalve feeding current, in a horizontal and in a vertical plane. Larval swimming behaviour in a suction flow field was reconstructed by subtracting local water movement vectors from the total movement of larvae, yielding movement paths due to larval swimming alone. Swimming speeds and the rate of displacement in vertical direction of C. gigas and M. edulis larvae were related to larval shell length, and to the pitch of up- or downward swimming. Larvae of both species did not show escape reactions in a suction flow field. With increasing shell length, larval swimming speeds of both species increased significantly. Swimming speeds of C. gigas larvae were significantly higher than swimming speeds of M. edulis larvae, resulting in a faster vertical displacement. The ability to migrate to more favourable water layers faster may offer C. gigas an advantage over native bivalves with slower swimming larvae.

A morphological and structural study of the larval shell from the abalone Haliotis tuberculata

The larval shell of the marine gastropod Haliotis tuberculata was investigated by polarised light microscopy, scanning electron microscopy, Raman microspectroscopy and infra-red spectroscopy. Trochophore and veliger larval sections were used for histological examination of the growing shell and each larval stage was related to the shell development and the appearance of calcified formations. We determined the stage of initial calcification by specific staining combined with polarised light examination. The shell of 30-h-old pre-veliger larvae was found to be mineralized, confirming that calcification occurred before larval torsion. Using both infra-red and Raman spectroscopy, we showed that CaCO3 deposition occurred at the pre-veliger stage and that the mineral phase initially deposited was essentially composed of aragonite.

Morphology of larvae of the family Mytilidae (Bivalvia) from the north-western part of the Sea of Japan

The larval shell morphology of 10 bivalve species of the family Mytilidae (Adula falcatoides,Crenella decussata,Crenomytilus grayanus,Modiolus kurilensis,Musculista senhousia,Mytilus coruscus,Mytilus galloprovincialis,Mytilus trossulusandSeptifer keenae, and an unidentified species Mytilidae indeterminate) from the Sea of Japan is described. The following morphological features were comparatively examined: larval shell outlines including shape and size of umbones, and anterior, posterior and ventral margins, hinge morphology, ligament location, sculpture, colour, and eye-spot outlines. Some dimensional parameters of larval shells are given. The time interval of occurrence of larvae in the plankton, water temperature in this period, and shell length of competent larvae are presented. It is demonstrated that, in spite of sometimes similar external morphological characters, identification of mytilid larvae creates no difficulties if all distinguishing characters are used.

Two Mississippian Caenogastropod limpets from Australia and their meaning for the ancestry of the Caenogastropoda

Two new limpets with a caenogastropod-type larval shell are described from the Mississippian (Early Carboniferous) of Australia and assigned toAustraloscutulan. gen. of the family Pragoscutulidae. This family has previously been reported only from the Early Devonian of Europe (Czech Republic, Prague Basin). Therefore, it survived the Late Devonian biotic crisis. the fact that one of the earliest certain caenogastropods has a patelliform shell is noteworthy given most other Middle to Late Paleozoic caenogastropods are high-spired or fusiform. Pragosutulidae are interpreted as an early patelliform caenogastropod offshoot derived from coiled ancestors. the Pragoscutulidae are the oldest gastropod limpets with well-preserved larval shells. Their teleoconch is entirely limpet-shaped without helicoid coiling. However, the helicoid turbiniform larval shells suggests that this group evolved from an ancestor with turbiniform or even high-spired adult shell. Moreover, the multi-whorled dextral larval shells show that Pragoscutulidae are Caenogastropoda and document that early Caenogastropoda displayed considerable disparity.

Comparative study of shell shape and muscle scar pigmentation in the closely related cupped oystersCrassostrea angulata,C. gigasand their reciprocal hybrids

The taxonomic status of the cupped oysters Crassostrea angulata and C. gigas has received considerable attention in the last decades. Based on larval shell morphology, experimental hybridization, allozymes and nuclear DNA studies several authors have considered these two taxa as being synonymous. However, mitochondrial data showed clear genetic differences between the two taxa. In addition, microsatellite-based studies and cytogenetic studies have also pro- vided evidence that supports their differentiation. Considerable differences have also been observed at the phenotypic level in terms of growth rate and ecophysiological parameters. In the present study, C. angulata from Sado estuary (Portugal) and C. gigas from Seudre estuary (France) were collected and factorial crosses were performed. Juveniles of the different progenies were reared in Ria Formosa (Portugal) under common conditions to determine if they exhibited differences in shell shape and in pigmentation of the adductor muscle scar. Significant morphometric differences be- tween C. angulata and C. gigas progenies were indicated by univariate and multivariate analyses. Univariate analysis of size-adjusted shell measurements revealed significant differences between the two taxa for shell depth, muscle scar height, and length of ligamental area. Both reciprocal hybrids showed intermediate morphometric characters between parental lines. In addition, significant differences were also observed between C. angulata and C. gigas progenies in terms of pigmentation of adductor muscle scar. C. angulata and both reciprocal hybrid progenies showed highly pig- mented adductor muscle scars whereas in C. gigas progeny the pigmentation was lighter. The differences in shell shape and muscle scar pigmentation observed in the present study support the distinction of the two taxa.

Size of the earliest mollusks: Did small helcionellids grow to become large adults?

Research Article| February 01, 2008 Size of the earliest mollusks: Did small helcionellids grow to become large adults? Mónica Martí Mus; Mónica Martí Mus 1Área de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain Search for other works by this author on: GSW Google Scholar Teodoro Palacios; Teodoro Palacios 1Área de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain Search for other works by this author on: GSW Google Scholar Sören Jensen Sören Jensen 1Área de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain Search for other works by this author on: GSW Google Scholar Author and Article Information Mónica Martí Mus 1Área de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain Teodoro Palacios 1Área de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain Sören Jensen 1Área de Paleontología, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain Publisher: Geological Society of America Received: 25 Jun 2007 Revision Received: 23 Oct 2007 Accepted: 24 Oct 2007 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 The Geological Society of America, Inc. Geology (2008) 36 (2): 175–178. https://doi.org/10.1130/G24218A.1 Article history Received: 25 Jun 2007 Revision Received: 23 Oct 2007 Accepted: 24 Oct 2007 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mónica Martí Mus, Teodoro Palacios, Sören Jensen; Size of the earliest mollusks: Did small helcionellids grow to become large adults?. Geology 2008;; 36 (2): 175–178. doi: https://doi.org/10.1130/G24218A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The generally accepted view that early mollusks were millimeter-scale animals is partly based on paleontological data. Millimeter-scale, exquisitely preserved mollusks are important constituents of many small shelly fossil assemblages and have been the focus of most modern studies of Cambrian mollusks. Centimeter-sized mollusks occur in the fossil record as early as the earliest Cambrian but have been neglected for decades in favor of their better-preserved, millimeter-scale counterparts. Here we present a large, limpet-like mollusk from the Lower Cambrian of Spain that preserves an apical shell indistinguishable from the millimeter-scale helcionellids that have come to epitomize the ancestral “conchiferan.” The Spanish fossils provide direct evidence that at least some millimeter-scale helcionellids represent juvenile or larval shells of large, limpet-like mollusks, suggesting that the presumed generalized small size of Cambrian mollusks may be a taphonomic artifact. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Development in Berthella californica (Gastropoda: Opisthobranchia) with comparative observations on phylogenetically relevant larval characters among nudipleuran opisthobranchs

Abstract. Morphological criteria defining the Nudipleura and sister group relationships among the three nudipleuran subgroups (pleurobranchoideans, anthobranch nudibranchs, and cladobranch nudibranchs) have been controversial. Analysis of larval stages may help resolve these uncertainties by identifying additional phylogenetically informative characters, but existing information on pleurobranchoidean larvae is meager. We studied larval development and metamorphosis of the pleurobranchoidean Berthella californica using histological sections, scanning and transmission electron microscopy, and immunolabeling of neurons within the larval apical ganglion. We also provide comparative data on other nudipleuran larvae that may be useful for phylogenetic reconstruction. Berthella californica fills a previously unoccupied place within an evolutionary scenario that derives nudibranchs from pleurobranchoideans, two groups in which the larval mantle fold forms the post‐metamorphic notum (dorsal epidermis). In B. californica, reflection of the mantle fold epithelium to form the notum begins at metamorphosis, as also occurs in nudibranchs, whereas mantle reflection in other pleurobranchoideans begins well before metamorphosis. Dissolution of overgrown shell walls inside the protoconch and formation of the post‐metamorphic notum from the inner epithelium of the larval mantle fold may be synapomorphies of the Nudipleura. The larval shell in B. californica is additionally noteworthy because it acquires bilateral symmetry later in development, which is very unusual among larval opisthobranchs. We demonstrate an osphradium in the larvae of two pleurobranchoideans and one anthobranch nudibranch, although adults lack this trait. We also identified an autapomorphy of cladobranch nudibranchs in the form of five ampullary neurons within the larval apical ganglion, whereas other planktotrophic opisthobranch larvae have only four of these neurons. Although our data provide morphological criteria defining both the Nudipleura and the cladobranch nudibranchs, they are insufficient to resolve sister group relationships within the Nudipleura.

AN EARLY CAMBRIAN ORGANOPHOSPHATIC BRACHIOPOD WITH CALCITIC GRANULES

Abstract: The linguliform brachiopod Eoobolus from the Early Cambrian Mural Formation (Jasper National Park, Canadian Rocky Mountains) exhibits various calcitic features in its otherwise apatitic shell. It is argued here that the decomposition of the organic matter within the shell led to a microenvironment similar to those resulting in the phosphatization of soft tissues. This diagenetic regime encouraged the initial precipitation of apatite cements followed by calcite cements. By fully coating primary structures early apatite cements separate primary structures from the later precipitation of calcite cement. Round calcareous grains, about 3 µm in size, that occur in the centre of apatite botryoids must therefore represent original components of the shell. The equivalent pits of such calcareous granules are seen in the larval shells of many Palaeozoic linguliform brachiopods. This suggests that mixed organophosphatic‐calcareous shells were relatively common at that time but that they have been overlooked owing to the obliteration of original calcareous structures by traditional acid preparation methods for the extraction of phosphatic fossils. The Eoobolus shell structure is intermediate between purely organophosphatic and calcitic shells. Although one such genus is not sufficient to reconstruct the ancestral composition of the brachiopod shell, it provides a means of recognizing other transitional forms that are needed to understand fully the shift in shell mineralogy.

An Extraordinarily Long Larval Duration of 4.5 Years from Hatching to Metamorphosis for Teleplanic Veligers ofFusitriton oregonensis

Veliger larvae of the NE Pacific snail Fusitriton oregonensis were reared in culture for 4.5 to 4.6 years from hatching to metamorphosis and through postlarval growth to reproduction. Larval shells grew in length from 0.20 to 3.9 mm. Late veligers grew slowly, but shell sizes increased even in the 4th and 5th years. Widths of larval shells at late stages equaled or exceeded those of the protoconchs of two juveniles from the field. Cultured larvae did not metamorphose until presented with subtidal rocks and associated biota. There was no indication of larval senescence: the first 2 years of postmetamorphic shell growth were slightly faster, and time from metamorphosis to first reproduction (3.3 years) was slightly less than for an individual that had developed to metamorphic competence in the plankton. A 4.5-year larval phase exceeds previous estimates for teleplanic larval durations and greatly exceeds estimates of the time for transport across oceans. This extraordinarily long larval period may exceed the usual duration in nature but shows that larval periods can be much longer than previously suspected without complete stasis in growth and with little if any loss of viability.

Dynamic expression of ancient and novel molluscan shell genes during ecological transitions

BackgroundThe Mollusca constitute one of the most morphologically and ecologically diverse metazoan phyla, occupying a wide range of marine, terrestrial and freshwater habitats. The evolutionary success of the molluscs can in part be attributed to the evolvability of the external shell. Typically, the shell first forms during embryonic and larval development, changing dramatically in shape, colour and mineralogical composition as development and maturation proceeds. Major developmental transitions in shell morphology often correlate with ecological transitions (e.g. from a planktonic to benthic existence at metamorphosis). While the genes involved in molluscan biomineralisation are beginning to be identified, there is little understanding of how these are developmentally regulated, or if the same genes are operational at different stages of the mollusc's life.ResultsHere we relate the developmental expression of nine genes in the tissue responsible for shell production – the mantle – to ecological transitions that occur during the lifetime of the tropical abalone Haliotis asinina (Vetigastropoda). Four of these genes encode evolutionarily ancient proteins, while four others encode secreted proteins with little or no identity to known proteins. Another gene has been previously described from the mantle of another haliotid vetigastropod. All nine genes display dynamic spatial and temporal expression profiles within the larval shell field and juvenile mantle.ConclusionThese expression data reflect the regulatory complexity that underlies molluscan shell construction from larval stages to adulthood, and serves to highlight the different ecological demands placed on each stage. The use of both ancient and novel genes in all stages of shell construction also suggest that a core set of shell-making genes was provided by a shared metazoan ancestor, which has been elaborated upon to produce the range of molluscan shell types we see today.

Larval shells of Late Palaeozoic naticopsid gastropods (Neritopsoidea: Neritimorpha) with a discussion of the early neritimorph evolution

Extant neritimorphs with planktotrophic larval development have a convolute smooth larval shell which is internally resorbed. The oldest known larval shells of this type are of Triassic age. Well-preserved Late Palaeozoic neritimorph specimens have larval shells of two or more rapidly increasing well separated whorls. These larval shells resemble planktotrophic caenogastropod larval shells. This type of larval shell is possibly plesiomorphic in neritimorphs and caenogastropods. Permian/Pennsylvanian neritimorphs (Naticopsis, Trachyspird) have smooth larval shells (Naticopsidae) or larval shells with strong axial ribs (Trachyspiridae new family). The convolute low-spired round shell shape of modern neritimorphs is causally linked with the resorption of the inner teleoconch and protoconch whorls. Modern neritimorph shells with a uniform, undifferentiated inner lumen have probably evolved from naticopsid ancestors which lack resorption. It is possible that an elevated spire, deep sutures and protruding spiral larval shells would have made such internally undifferentiated shells more vulnerable for mechanical destruction and predation. Suggestions that coiling evolved independently in neritimorphs and other Gastropoda are unlikely and contrast with the fossil record. The modern neritid larval shell has probably evolved from relatively low-spired smooth naticopsid larval shells like those reported here.

Laser ablation ICP‐MS analysis of larval shell in softshell clams (Mya arenaria) poses challenges for natural tag studies

We investigated whether laser ablation inductively coupled plasma mass spectrometry (ICP‐MS) could be used to quantify larval shell compositions of softshell clams, Mya arenaria. The composition of aragonitic otoliths has been used as a natural tag to identify natal habitat in connectivity studies of fish. If it is possible to measure larval shell reliably, this technique could also be applied to marine bivalves. To determine whether the first larval shell (prodissoconch I) could be measured independent of underlying material, we conducted laboratory experiments in which larval M. arenaria were exposed to enrichments of the stable isotope 138Ba during different stages in shell development. We were unable to isolate the chemical signature of the prodissoconch I from subsequent life stages in all combinations of shell preparation and instrument settings. Typical instrument settings burned through the prodissoconch I on a post‐settlement juvenile and at least 9 d of second larval shell (prodissoconch II) growth. Our results suggest instrumental and technical improvements are needed before laser ablation ICP‐MS can be useful for connectivity studies that require analysis of larval shell on a post‐settlement M. arenaria juvenile. Laser burn‐through is potentially a problem in any connectivity study where it is necessary to assay the small amounts of shell material that are deposited before a larva disperses away from its natal location.

Origin of planktotrophy—evidence from early molluscs: a response to Freeman and Lundelius

Evolution & DevelopmentVolume 9, Issue 4 p. 313-318 Origin of planktotrophy—evidence from early molluscs: a response to Freeman and Lundelius Alexander Nützel, Corresponding Author Alexander Nützel Bayerische Staatssammlung für Paläontologie und Geologie (Bavarian State Collection for Paleontology and Geology), Richard-Wagner-Str. 10, 80333 München, Germany*Author for correspondence (email: a.nuetzel@lrz.uni-muenchen.de)Search for more papers by this authorOliver Lehnert, Oliver Lehnert Institut für Geologie und Mineralogie, Universität Erlangen, Schlossgarten 5, D-91054 Erlangen, GermanySearch for more papers by this authorJiří Frýda, Jiří Frýda Czech Geological Survey, Klárov 3/131, 118 21 Prague 1, Czech RepublicSearch for more papers by this author Alexander Nützel, Corresponding Author Alexander Nützel Bayerische Staatssammlung für Paläontologie und Geologie (Bavarian State Collection for Paleontology and Geology), Richard-Wagner-Str. 10, 80333 München, Germany*Author for correspondence (email: a.nuetzel@lrz.uni-muenchen.de)Search for more papers by this authorOliver Lehnert, Oliver Lehnert Institut für Geologie und Mineralogie, Universität Erlangen, Schlossgarten 5, D-91054 Erlangen, GermanySearch for more papers by this authorJiří Frýda, Jiří Frýda Czech Geological Survey, Klárov 3/131, 118 21 Prague 1, Czech RepublicSearch for more papers by this author First published: 20 July 2007 https://doi.org/10.1111/j.1525-142X.2007.00166.xCitations: 20Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume9, Issue4July/August 2007Pages 313-318 RelatedInformation

KYLLINIA PARENTALIS (NEOGASTROPODA: TURRIDAE), NEW GENUS AND SPECIES FROM THE PLIO–PLEISTOCENE OF THE CENTRAL MEDITERRANEAN AREA

Abstract A new genus and species of turrid neogastropod, Kyllinia parentalis, is described based on three shells from the Pliocene (North Italy) and the Pleistocene (northwestern Peloponnesus) of the central Mediterranean area. The new taxon is compared to the buccinid (sensu lato) genus Metula H. and A. Adams, 1853 with which it shows a few superficial similarities mainly limited to the latticed sculptural pattern of the teleoconch. Kyllinia parentalis is placed in the turrid subfamily Mangeliinae on the basis of teleoconch characters (double sinuosity of the outer lip and the short, forward curved anterior canal) and protoconch (a characteristic pattern formed by narrow axial riblets giving a coronated suture to the larval shell). These taxonomic characters, together with the almost clathrate teleoconch sculpture, form an original combination within the Mangeliinae, thus justifying the description of a new genus. The Recent species Philbertia marchadi Knudsen, 1956 (for which we consider the previous at...

First finds of larval shells of Ordovician craniids in the Pskov Region

The inner surface of the dorsal valve at the early developmental stages and the larval shells lacking adult shell are described for the first time for the Ordovician craniids. The presence of a larval calcareous shell in the Early Paleozoic craniids is proposed.

Settlement of larval top shell Turbo�(Batillus)�cornutus in response to several marine algae

The settlement of larval top shell Turbo (Batillus) cornutus in response to seven macroalgal and three benthic diatom species was examined in the laboratory. The percentages of larval settlement different significantly among algal species, and were significantly higher on two red algal species (Marginisporum crassissima, an articulated coralline alga, and Gelidium elegans, an agarophyte) than on the green algae, brown algae and benthic diatoms tested. Marginisporum crassissima induced larval settlement most strongly throughout the experiments. The percentage of larval settlement on a crustose coralline alga (unidentified species), which is known as a suitable substratum for abalone larvae, was much lower than on M. crassissima and G. elegans, which have morphologically complex growth forms. The percentage of settled individuals on ethanol-killed M. crassissima was much lower than on intact M. crassissima. The results indicate that physical structure is unlikely to be the main inducer of settlement; therefore, settlement of top shell larvae seems to be strongly induced by chemicals from the two red algal species. The specific distribution of juvenile top shell in the field may be at least partly determined by the strong induction of larval settlement by articulated coralline and gelidiacean algae.

Similar reproductive cycles and life‐history traits in congeneric limid bivalves with different modes of nutrition

AbstractWe have studied two congeneric limid bivalves, Acesta species novum and Acesta excavata (Bivalvia: Limidae), that live in similar physical conditions but use different food sources. Acesta sp. nov. live on the giant siboglinid tubeworm Lamellibrachia luymesi at cold seeps and feed on their eggs, a continuous food source that ultimately is derived from chemosynthesis, whereas A. excavata relies on planktonic food of photosynthetic origin, which varies seasonally. We hypothesized that these two species might show differences in the periodicity of reproduction; specifically, we predicted that A. sp. nov. would breed continuously and that A. excavata would demonstrate an annual reproductive cycle. Our hypothesis was refuted, as both species have a semi‐continuous reproductive cycle. Food quality, quantity or seasonality had no clear effect. Reproductive adults are functionally gonochoristic. Females broadcast buoyant eggs with an average size of 179 μm in A. sp. nov. and 160 μm in A. excavata. Both the size of the larval shell and the size of the spawned eggs are suggestive of pelagic lecithotrophic development. Both species also appear to be protandric hermaphrodites, changing from male to female at approximately 77 and 90 mm shell height, respectively, although not all individuals change sex. In the material investigated in this study there was a biased sex ratio favouring males.

The structure of mollusc larval shells formed in the presence of the chitin synthase inhibitor Nikkomycin Z.

BackgroundChitin self-assembly provides a dynamic extracellular biomineralization interface. The insoluble matrix of larval shells of the marine bivalve mollusc Mytilus galloprovincialis consists of chitinous material that is distributed and structured in relation to characteristic shell features. Mollusc shell chitin is synthesized via a complex transmembrane chitin synthase with an intracellular myosin motor domain.ResultsEnzymatic mollusc chitin synthesis was investigated in vivo by using the small-molecule drug NikkomycinZ, a structural analogue to the sugar donor substrate UDP-N-acetyl-D-glucosamine (UDP-GlcNAc). The impact on mollusc shell formation was analyzed by binocular microscopy, polarized light video microscopy in vivo, and scanning electron microscopy data obtained from shell material formed in the presence of NikkomycinZ. The partial inhibition of chitin synthesis in vivo during larval development by NikkomycinZ (5 μM – 10 μM) dramatically alters the structure and thus the functionality of the larval shell at various growth fronts, such as the bivalve hinge and the shell's edges.ConclusionProvided that NikkomycinZ mainly affects chitin synthesis in molluscs, the presented data suggest that the mollusc chitin synthase fulfils an important enzymatic role in the coordinated formation of larval bivalve shells. It can be speculated that chitin synthesis bears the potential to contribute via signal transduction pathways to the implementation of hierarchical patterns into chitin mineral-composites such as prismatic, nacre, and crossed-lamellar shell types.

Ecological implications of molluscan ontogenetic strategies ‐ examples from aquatic ecosystems of the Cenozoic Iberian Peninsula

Molluscs from marginal marine and intra-continental basins of the Iberian Peninsula are described with special emphasis on the early ontogenetic shell formation, which reflects the embryogenesis and larval ecology. The fossils, covering a time span from the Early Oligocene to the Early Pleistocene, are compared to contemporaneous fossil faunas of the Mediterranean and Paratethys, and to extant Mediterranean faunas. Larval shells occur in bivalves and gastropods of Upper Tortonian coastal lagoons near Crevillente (Alicante), indicating marine larval stages and a connection of the adult habitat with the open sea. The euryhaline marginal marine gastropods display planktotrophic larval shells, which enable a marine distribution, but prevented generally euryhaline genera, such as Granulolabium and Terebralia (Cerithioidea, Potamididae), from colonizing continental saline ecosystems. The establishment of athalassic saline populations implies the preadaptational loss of planktotrophy. For the first time lecithotrophic larval development in an athalassic saline system is documented for Potamides gaudryi (Cerithioidea, Potamididae) from the late Middle to early Upper Miocene of the Duero Basin. With regard to the early ontogenetic development, P. gaudryi is distinguished from its possible descendant, the extant Potamides conicus (Blainville, 1829), which represents a direct developer that lacks any larval stage. In comparison to direct development, lecithotrophic larval development was advantageous in the colonization of temporary habitats, such as flood areas. Two different modes of direct development with hatching of crawling young are documented: Feeding on embryonic yolk until the hatching stage and adelphophagy. Adelphophagous embryonic development appears to be advantageous in neritids, thiarids and pulmonates that live in habitats with strong predation of juvenile fishes based on the advanced developmental stage and larger shell size of the hatchlings.

Larval rearing of calico scallops, Argopecten gibbus, in a flow-through system

A flow-through (FT) culture system is described for calico scallop, Argopecten gibbus, larvae. Its performance was assessed by larval survival rate, shell growth, settlement rate and post-larval shell growth for the duration of larval life (13 days). Comparisons were made with larvae reared in standard static system (S). Effect of increased larval density on FT performance was also investigated. With comparable larval densities, survival rate of Day 2 larvae to pediveliger stage was similar in both larval rearing systems. Shell growth for FT-reared larvae was comparable or significantly higher than in the static system (P < 0.01). Settlement rate of pediveligers was comparable for both systems, averaging 30.7%, and no significant difference was seen in shell growth of FT- and static-reared pediveligers. Increased initial larval density did not affect survival rate in FT, but did negatively affect larval shell growth, settlement rate and post-larval shell growth yielding lower growth and minimal settlement rate (10.9 ± 2.8%) compared to the static system. This FT system was successful as larval rearing system, optimising space allocation in the hatchery, reducing labour, and eliminating the use of antibiotics. Optimising initial larval density within the system needs to be investigated in association with food ration.