Changes in the timing of mantle formation and larval life history traits in linguliform and craniiform brachiopods

The distribution of embryonic and larval mantles is documented in linguliform and craniiform brachiopods. Criteria are presented for identifying these mantle types. The mantle type is related to planktotrophic and lecithotrophic larval life history patterns. In the Linguliformea and Craniiformea, all Lower Palaeozoic families with adequate preservation had larval mantles, indicating the presence of a planktotrophic larva. Heterochronic changes in the time of mantle origin, from the larval to the embryonic stage of development, has occurred several times. In the Lingulidae this change appears to have taken place at about the time the family originated in the Devonian and has been retained in extant genera. The family Discinidae has also retained a planktotrophic larval stage from the Lower Palaeozic to the present. The extant genus Crania in the Craniidae has a short-lived lecithotrophic larva that lacks a mantle. Through the Lower Jurassic, this family had planktotrophic larvae with a larval shell. During the Upper Jurassic, genera with a lecithotrophic larva that lacked a larval shell began to appear; however, the last genera in this family with a planktotrophic larva and a larval shell did not become extinct until the Tertiary.     

Larval ecology and morphology in fossil gastropods

The shell of marine gastropods conserves and reflects early ontogeny, including embryonic and larval stages, to a high degree when compared with other marine invertebrates. Planktotrophic larval development is indicated by a small embryonic shell (size is also related to systematic placement) with little yolk followed by a multiwhorled shell formed by a free‐swimming veliger larva. Basal gastropod clades (e.g. Vetigastropoda) lack planktotrophic larval development. The great majority of Late Palaeozoic and Mesozoic ‘derived’ marine gastropods (Neritimorpha, Caenogastropoda and Heterobranchia) with known protoconch had planktotrophic larval development. Dimensions of internal moulds of protoconchs suggest that planktotrophic larval development was largely absent in the Cambrian and evolved at the Cambrian–Ordovician transition, mainly due to increasing benthic predation. The evolution of planktotrophic larval development offered advantages and opportunities such as more effective dispersal, enhanced gene flow between populations and prevention of inbreeding. Early gastropod larval shells were openly coiled and weakly sculptured. During the Mid‐ and Late Palaeozoic, modern tightly coiled larval shells (commonly with strong sculpture) evolved due to increasing predation pressure in the plankton. The presence of numerous Late Palaeozoic and Triassic gastropod species with planktotrophic larval development suggests sufficient primary production although direct evidence for phytoplankton is scarce in this period. Contrary to previous suggestions, it seems unlikely that the end‐Permian mass extinction selected against species with planktotrophic larval development. The molluscan classes with highest species diversity (Gastropoda and Bivalvia) are those which may have planktotrophic larval development. Extremely high diversity in such groups as Caenogastropoda or eulamellibranch bivalves is the result of high phylogenetic activity and is associated with the presence of planktotrophic veliger larvae in many members of these groups, although causality has not been shown yet. A new gastropod species and genus, Anachronistella peterwagneri, is described from the Late Triassic Cassian Formation; it is the first known Triassic gastropod with an openly coiled larval shell.     

New results of the “EPOS” leg 3 cruise to antarctica: Horizontal and vertical distribution of isopods (Crustacea) in the eastern Weddell Sea

Summary A comparison of the EPOS leg 3 material of Weddell Sea Isopoda with the known literature data revealed some new results for the horizontal and vertical distribution of isopods in the eastern Weddell Sea. The number of isopod species known for the Weddell Sea almost doubled to 118 species. New results on the vertical distribution of 11 isopod genera are presented.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Inferring larval type in fossil bryozoans

Pachut, J.F. & Fisherkeller, P. 2010: Inferring larval type in fossil bryozoans. Lethaia, Vol. 43, pp. 396–410. Larval type in extinct organisms might be recognizable because larvae of living marine invertebrates are approximately of the same size as the initial post‐larval organism. Two larval types typically occur. Planktotrophic larvae feed on other members of the plankton, potentially prolonging their larval existence and producing broad geographic distributions. Conversely, lecithotrophic larvae feed on yolk supplied by the fertilized egg, often settle quickly after release, and display more restricted distributions. However, some lecithotrophic bryozoans undergo embryonic fission forming multiple, small, polyembryonic larvae. The relationship between post‐larval size and larval type was evaluated in bryozoans by comparing the size of the ancestrula, the founding individual of a colony, to the sizes of extant planktotrophic, lecithotrophic and polyembryonic lecithotrophic larvae and ancestrulae. The sizes of larvae and ancestrulae in extant lecithotrophic and planktotrophic cheilostome (gymnolaemate) species are statistically the same. They are, however, statistically larger than the polyembryonic larvae of extant cyclostomes (stenolaemates). In turn, the sizes of cyclostome larvae are indistinguishable from the ancestrulae of extant and fossil cyclostomes, the ancestrulae of other fossil stenolaemate species measured from the literature, and the ancestrulae of three of four genera from North American Cincinnatian strata. Ancestrulae of a fourth genus, Dekayia, are the same size as cyclostome ancestrulae but are statistically smaller than the ancestrulae of other stenolaemates. With few exceptions, stenolaemates have statistically smaller larvae and ancestrulae than both lecithotrophic and planktotrophic cheilostomes. We infer that the sizes of fossil ancestrulae permit the discrimination of taxa that had polyembryonic lecithotrophic larvae from those possessing other larval types. This inference is strengthened, in several cases, by the co‐occurrence of brood chambers (gynozooecia) and restricted palaeobiogeographic distributions. The presence of cyclostomes in Early Ordovician strata suggests that polyembryony may have been acquired during the initial radiation of Class Stenolaemata. Polyembryony appears to be a monophyletic trait, but confirmation requires the demonstration that species of several stenolaemate suborders lacking skeletally expressed brood chambers possessed polyembryonic larvae. □Ancestrulae, evolution, fossil bryozoans, gynozooecia, larvae.     

Taxonomic composition and interannual variations in numerical density of meroplankton in the Sea of Azov

This paper presents data on the taxonomic composition and dynamics of numerical density of meroplankton in the Sea of Azov. Studies performed in June 2003–2005 revealed benthic invertebrate larvae of 26 taxa: Polychaeta, 7; Cirripedia, 1; Decapoda, 5; Gastropoda, 5; and Bivalvia, 8. Meroplankton was dominated by larvae of species that are able to endure considerable concentrations of pollution by labile sulfides in bottom sediments and eutrophication: Mytilaster lineatus, Cerastoderma sp., Abra ovata (Philippi), Hydrobia acuta (Gastropoda), and Amphibalanus improvisus (Cirripedia). The spatial and temporal variations in the structure of dominant species and numerical abundance of meroplankton in the Sea of Azov are likely to be associated with water temperature fluctuations, pelagic predators, and eutrophication. Under anthropogenic stress and predation pressure, most larvae of benthic invertebrates are apparently unable to complete metamorphosis and contribute to recruitment to parental populations. Thus, the numerical density of meroplankton in the Sea of Azov can significantly vary, even over one month.     

Larvae of the deep-sea Nematocarcinidae (Crustacea: Decapoda: Caridea) from the Southern Ocean

The early larval stages of the deep-sea Nematocarcinidae, Nematocarcinus longirostris Bate, 1888, from the south-western Atlantic Ocean, and N. lanceopes Bate, 1888, from the high Antarctic Weddell Sea, were obtained from plankton catches, described and illustrated. Furthermore, field collected larvae of N. lanceopes were compared with larvae hatched and reared under constant laboratory conditions. The morphology of larvae in both species clearly indicates a planktotrophic and extended mode of larval development. This is an outstanding feature in deep-sea and especially in high-latitudinal caridean shrimp species, and the consequence of such reproductive trait for life history adaptations to both deep-sea and polar environments is discussed.This revised version was published online in November 2004 with corrections to the figure part lettering.     

Biogeographic and bathymetric ranges of Atlantic deep-sea echinoderms and ascidians: the role of larval dispersal

Dispersal plays an important role in the establishment and maintenance of biodiversity and, for most deep-sea benthic marine invertebrates, it occurs mainly during the larval stages. Therefore, the mode of reproduction (and thus dispersal ability) will affect greatly the biogeographic and bathymetric distributions of deep-sea organisms. We tested the hypothesis that, for bathyal and abyssal echinoderms and ascidians of the Atlantic Ocean, species with planktotrophic larval development have broader biogeographic and bathymetric ranges than species with lecithotrophic development. In comparing two groups with lecithotrophic development, we found that ascidians, which probably have a shorter larval period and therefore less dispersal potential, were present in fewer geographic regions than elasipod holothurians, which are likely to have longer larval periods. For asteroids and echinoids, both the geographic and bathymetric ranges were greater for lecithotrophic than for planktotrophic species. For these two classes, the relationships of egg diameter with geographic and bathymetric range were either linearly increasing or non-monotonic. We conclude that lecithotrophic development does not necessarily constrain dispersal in the deep sea, probably because species with planktotrophic development may be confined to regions of high detrital input from the sea surface. Our data suggest that more information is necessary on lengths of larval period for different species to accurately assess dispersal in the deep sea.     

The Diversity of Strategies of Defense from Pathogens in Molluscs

Based on our own results and literature data, a comparative analysis is performed of particularities of mechanisms of defense from pathogens in representatives of Bivalvia and Gastropoda. The agglutinating and opsonizing activities of plasma from molluscs of phylogenetically distant species were revealed to differ significantly. These differences may be described in terms of two contrast strategies: low-promiscuous that is more typical of most gastropod mollusc species, it is characterized by a narrow specificity of plasma agglutinins and a strong dependence of phagocytosis on the presence of plasma proteins in the medium; the high-promiscuous strategy is characteristic predominately of bivalve molluscs whose plasma agglutinins are able to react with a wider spectrum of indicator cells, and the rate of phagocytosis in this case does not depend on the presence of plasma proteins in the medium. The diversity of strategies of defense from pathogens can explain differences in spectra of pathogen organisms parasitizing in Gastropoda and Bivalvia.     

Aufbau, Variabilit?t und m?gliche Funktionen des Rufduetts beim ThermometerhuhnLeipoa ocellata

Zusammenfassung Beim ThermometerhuhnLeipoa ocellata tragen die Partner eine Paares ein Rufduett vor. Der Anteil des besteht aus einer Rufreihe, die sich aus einer Folge von 2–7 identischen, zweisilbigen Rufen zusammensetzt. Das trägt einen einzelnen, obertonreichen und langgezogenen Ruf vor. Sowohl der Ruf des als auch die Rufreihe des wird in Serien vorgetragen. Innerhalb einer solcher Ruf- bzw. Rufreihenserie können mehrere Duette auftreten. Die Rufe sind jedoch nicht ausschließlich an das Duett gebunden. Die Variabilität im Aufbau des Duetts äußert sich im Zeitpunkt des Einsatzes des antwortenden Vogels, in der Anzahl der -Rufe während des Duetts und in der Anzahl der Einheiten, aus denen sich der Duettanteil des zusammensetzt. Das beginnt signifikant häufiger als das eine Serie, in der ein oder mehrere Duette vorkommen. Ebenso ist es häufiger der Initiator des ersten in dieser Serie liegenden Duetts. Das Duett dient wohl hauptsächlich zur Festigung des Zusammenhalts zwischen den Paarpartnern. Es erfüllt jedoch von seinen physikalischen Eigenschaften her auch die Bedingungen, die für ein territorial wirksames Signal gelten.

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Structure, variability and possible functions of duetting in the Mallee FowlLeipoa ocellata

Summary In the Australian Mallee Fowl,Leipoa ocellata, both and of a pair are involved in a call duet. The part of the consists of a sequence of 2–7 identical two-syllable calls. The contributes a single long-drawn-out call rich in harmonics. The call of the as well as the call sequence of the are presented in series. Within a series of calls () or call sequences () several duets can occur. The respective vocalizations, however, do not exclusively occur during the duet.The variability in the details of the duet expresses itself in the lag period after which the mate responds, in the number of -calls during the duet, and in the number of calls within the call sequence of the . The begins a series during which one or several duets occur significantly more frequently than the . The circumstances under which duetting occurs indicate that duet calling mainly serves to maintain the pair bond. Moreover, due to its physical characteristics the duet also seems to be suited to serve as a territorial signal.

     

Poecilogony and population genetic structure in Elysia pusilla (Heterobranchia: Sacoglossa), and reproductive data for five sacoglossans that express dimorphisms in larval development

Credible cases of poecilogony, the production of two distinct larval morphs within a species, are extremely rare in marine invertebrates, yet peculiarly common in a clade of herbivorous sea slugs, the Sacoglossa. Only five animal species have been reported to express dimorphic egg sizes that result in planktotrophic and lecithotrophic larvae: the spionid polychaete Streblospio benedicti and four sacoglossans distributed in temperate estuaries or the Caribbean. Here, we present developmental and genetic evidence for a fifth case of poecilogony via egg-size dimorphism in the Sacoglossa and the first example from the tropical Indo-Pacific. The sea slug Elysia pusilla produced both planktotrophic and lecithotrophic larvae in Guam and Japan. Levels of genetic divergence within populations were markedly low and rule out cryptic species. However, divergence among populations was exceptionally high (10-12% at the mitochondrial cytochrome c oxidase I locus), illustrating that extensive phylogeographic structure can persist in spite of the dispersal potential of planktotrophic larvae. We review reproductive, developmental, and ecological data for the five known cases of poecilogony in the Sacoglossa, including new data for Costasiella ocellifera from the Caribbean. We hypothesize that sacoglossans achieve lecithotrophy at smaller egg sizes than do related clades of marine heterobranchs, which may facilitate developmental plasticity that is otherwise vanishingly rare among animals. Insight into the environmental drivers and evolutionary results of shifts in larval type will continue to be gleaned from population-level studies of poecilogonous taxa like E. pusilla, and should inform life-history theory about the causes and consequences of alternative development modes in marine animals.     

Invasion of the North American Atlantic Coast by a Large Predatory Asian Mollusc

The large Asian gastropod mollusc Rapana venosa Valenciennes 1846 (Neogastropoda, formerly Muricidae, currently Thaididae) is reported for eastern North America in the lower Chesapeake Bay and James River, Virginia, USA. This record represents a transoceanic range expansion for this carnivorous species. This species has previously been introduced to the Black Sea, Adriatic Sea, and Aegean Sea. Ballast water transport of larval stages from the eastern Mediterranean or Black Sea is the suspected vector of introduction into the Chesapeake Bay; 650 adult specimens in the size range 68–165mm shell length (SL) have been collected from hard sand bottom in depths ranging from 5 to 20m at salinities of 18–28ppt. The absence of small individuals from local collections is probably related to bias in collection methods. Age of the specimens could not be determined. R. venosa is probably capable of reproducing in the Chesapeake Bay. Egg cases of R. venosa were collected from Hampton Roads, a section of the James River, in August 1998, and hatched over a 21-day period under laboratory conditions to release viable bilobed veliger larvae. Four lobed larvae developed 4 days post-hatching and apparent morphological metamorphic competency was observed 14–17 days post-hatching. Despite the provision of live substrates and/or metamorphic inducers no metamorphosis to a crawling form was observed for larvae cultured on the monospecific diet. In work performed during 1999 settlement was observed for larvae cultured on a diet of mixed flagellates and diatoms and subsequently exposed to local epifaunal species. Salinity tolerance tests were performed on larvae at 1–6 days post-hatching. No deleterious effects were observed at salinities as low as 10ppt with limited survival to 7ppt at 6 days post-hatch. Current distribution is considered in context with larval salinity tolerance tests and literature describing native Asian and introduced populations to assess potential for establishment and further range extension both within the Chesapeake Bay and along the Atlantic coast of North America. Establishment within the Bay mainstem to the Rappahannock River with minor incursions into the mouths of the southerly subestuaries is considered feasible. A projected breeding range on the Atlantic seaboard extending from Cape Cod to Cape Hatteras is considered as tenable. Potential impact of R. venosa on commercially valuable shellfish stocks throughout the projected range is cause for serious concern. Boring by the polychaete Polydora websteri is more prevalent in the younger whorls of the shell, and absent in shell laid down later in life. This pattern suggests that juvenile animals may prefer hard substrates and not adopt an infaunal lifestyle until a size in excess of 50mmSL, or after reaching maturity.     

Structure of the first-formed shell of the Middle Ordovician orthid-like brachiopods from the Leningrad Region

Shell structure of the first-formed shell of the Middle Ordovician orthid-like brachiopods from the Leningrad Region is described. The 190-μm-wide first-formed shell is composed of finely granular layer while 700-μm-wide first-formed shell is fibrous. Thus the order Orthida in the Early Paleozoic included brachiopods with both planktotrophic and lecithotrophic larvae in the ontogeny.     

Developmental dimorphism: consequences for larval behavior and dispersal potential in a marine gastropod

Specific effects of alternative developmental programs on swimming and settlement behavior for marine larvae have not been identified experimentally. A major impediment to this research has been the rarity of species with variable development. Here, we compared traits related to movement and habitat selection for different ontogenetic stages of long-lived, feeding larvae (planktotrophic) and short-lived, nonfeeding larvae (lecithotrophic) of the herbivorous gastropod Alderia modesta. Newly hatched planktotrophic larvae swam in meandering paths with equal rates of upward and downward movement. As planktotrophic larvae developed towards competence (physiological ability to metamorphose), their swimming paths became straighter, faster, and increasingly directed towards the bottom, traits shared by newly hatched lecithotrophic larvae. Despite differing in developmental history, competent planktotrophic (32-d-old) and lecithotrophic larvae (competent upon hatching) exhibited qualitatively similar swimming behaviors and substrate specificity. However, lecithotrophic larvae moved downward at twice the speed of competent planktotrophic larvae, potentially producing a 5-fold higher rate of contact with the bottom in natural flows. Competent larvae swam downwards rather than passively sinking, even though sinking rates were faster than swimming speeds; active swimming may allow larvae to keep the velum extended, permitting rapid response to chemical settlement cues and promoting successful habitat colonization. Differences between larvae of the two development modes may reflect fine-tuning by selection of traits important for dispersal and settlement into patchy adult habitats.     

Diversity and distribution of molluscan fauna of Asthamudi estuary,Kerala, India

The survey of molluscan fauna of Ashtamudi estuary of the southwest coast of India recorded the presence of 119 species classified under 3 classes (Polyplacophora, Gastropoda and Bivalvia), 57 families and 96 genera. The species diversity was dominated by the Gastropoda (69 species), followed by the Bivalvia (49 species) and the Polyplacophora (1 species). The report includes four species recorded for the first time from India: Desmaulus edgarianus (Melvill, 1898), Pilosabia trigona (Gmelin, 1791), Nassarius javanus (Schepman, 1891) and Jorunna labialis (Eliot, 1908). The true diversity of the mangrove region was as good as that of a community with 31.380 (=?31) equally common species; the respective values for the bar mouth and lake regions were 15.516 and 8.997, respectively, indicating that the molluscan species assemblage of the mangrove was the most diverse and of the lake, the least. True β-diversity across this gradient registered 1.792, which means that though there were three communities, they were equivalent to only 1.792 (=?2) effective communities, i.e., the three actual communities were as different from each other as 2 with equal weights and no species in common.

     

Morphogenesis and phenotypic divergence in two developmental morphs of Streblospio benedicti (Annelida,Spionidae)

Abstract. The morphology of marine invertebrate larvae is strongly correlated with egg size and larval feeding mode. Planktotrophic larvae typically have suites of morphological traits that support a planktonic, feeding life style, while lecithotrophic larvae often have larger, yolkier bodies, and in some cases, a reduced expression of larval traits. Poecilogonous species provide interesting cases for the analysis of early morphogenesis, as two morphs of larvae are produced by a single species. We compared morphogenesis in planktotrophic and lecithotrophic morphs of the poecilogonous annelid Streblospio benedicti from the trochophore stage through metamorphosis, using observations of individuals that were observed alive, with scanning electron microscopy, or in serial sections. Offspring of alternate developmental morphs of this species are well known to have divergent morphologies in terms of size, yolk content, and the presence of larval bristles. We found that some phenotypic differences between morphs occur as traits that are present in only one morph (e.g., larval bristles, bacillary cells on the prostomium and pygidium), but that much of the phenotypic divergence is based on heterochronic changes in the differentiation of shared traits (e.g., gut and coelom). Tissue and organ development are compared in both morphs in terms of their structure and ontogenetic change throughout early development and metamorphosis.     

The Larval Development of the Chiton <Emphasis Type="Italic">Deshayesiella curvata</Emphasis> (Carpenter in Dall, 1879) (Mollusca: Polyplacophora)

Chronological study of the larval development of the chiton Deshayesiella curvata with sketching of the first stages of egg division and embryos up to the seven-valved shell stage is presented for the first time. D. curvata exhibits pelagic development with lecithotrophic larvae. Larval eyes form at the age of 3 days; at the age of 6 days, a Schwabe organ appears near the eyes in the form of two pigmented spots. Chitons at the stage of seven-valved shell have larval eyes, as well as the Schwabe organ.     

Larval Development and Metamorphosis in Sipuncula

In a brief review of development of the phylum Sipuncula, fourpatterns of development are recognized: (1) direct with no pelagicstage; (2) one larval stage, a lecithotrophic trochophore; (3)two larval stages, a lecithotrophic trochophore and a lecithotrophicpelagosphera; (4) two larval stages, a lecithotrophic trochophoreand a planktotrophic pelagosphera. Larval types and their metamorphosesare described, with special attention to the development andmorphology of the larval cuticle. In the majority of speciesstudied, the egg envelope is transformed into the larval cuticleat metamorphosis of the trochophore. The cuticle of many planktotrophicpelagosphera larvae is characterized by surface papillae ofdiverse form and pattern. The underlying cuticle in some speciesis composed of layers of fibers at right angles to one another.     

Density Dynamics and Size Composition of Bivalve Mollusk Larvae of the Genus Mya in Peter the Great Bay (Sea of Japan)

The seasonal population size of planktonic larvae of mollusks of the soft-shell clam genus Mya were studied in Vostok Bay. The larvae occurred in plankton from the first third of June to early September. The highest density of larvae (279.7 ± 98.7 specimens/m³) was found in late June. In early July, larval numbers decreased sharply, and at the end of the first third of July, only single Mya larvae were found in the plankton. Another increase in larval population was observed in early and late August. The larvae varied in length from 175 to 325 m in June–July and from 150 to 250 m in August. It is likely that the larvae of two species of Mya, M. arenaria and M. uzenensis, are present in the plankton of Vostok Bay.