Planktotrophic Larval Stage Research Articles

Temperature influences immune cell development and body length in purple sea urchin larvae

Anthropogenic climate change has increased the frequency and intensity of marine heatwaves that may broadly impact the health of marine invertebrates. Rising ocean temperatures lead to increases in disease prevalence in marine organisms; it is therefore critical to understand how marine heatwaves impact immune system development. The purple sea urchin (Strongylocentrotus purpuratus) is an ecologically important, broadcast-spawning, omnivore that primarily inhabits kelp forests in the northeastern Pacific Ocean. The S. purpuratus life cycle includes a relatively long-lived (∼2 months) planktotrophic larval stage. Larvae have a well-characterized cellular immune system that is mediated, in part, by a subset of mesenchymal cells known as pigment cells. To assess the role of environmental temperature on the development of larval immune cells, embryos were generated from adult sea urchins conditioned at 14 °C. Embryos were then cultured in either ambient (14 °C) or elevated (18 °C) seawater. Results indicate that larvae raised in an elevated temperature were slightly larger and had more pigment cells than those raised at ambient temperature. Further, the larval phenotypes varied significantly among genetic crosses, which highlights the importance of genotype in structuring how the immune system develops in the context of the environment. Overall, these results indicate that larvae are phenotypically plastic in modulating their immune cells and body length in response to adverse developmental conditions.

Artificial rearing of Actinopyga lecanora (Holothuroidea: Holothuriida) with spawning induction using relaxin: Lecithotrophic short larval period

Artificial rearing techniques of larvae and juveniles of the tropical sea cucumber, Actinopyga lecanora were developed for the first time. Broodstock individuals were collected in Yaeyama Islands, Okinawa, subtropical Japan and sorted by the gonad maturity which was determined by biopsy. An artificially-synthesized relaxin peptide, originated from Holothuria (Metriatyla) scabra, was injected into the coelomic fluid of mature A. lecanora at amounts of 3 × 10−9 to 10 × 10−9 mol kg−1 body weight, which successfully induced spawning in 10 of 14 females and 3 of 3 males after 26–70 min. The number of eggs spawned per one female individual ranged 2.2–9.5 × 105. The mean diameter of oocytes of A. lecanora individuals which spawned by the induction was 324 ± 13 μm, much larger than those of sea cucumber species having a planktotrophic larval stage. The embryo hatched during gastrula, and the larva metamorphosed to planktonic auricularia followed by doliolaria and finally settled into the benthic stage as pentactula. Time after fertilization to settlement was 4–8 days when larvae were reared in 5–500 L tanks at 26–28 °C, which is one of the shortest development periods among sea cucumbers. Although larvae were supplied with Chaetoceros gracilis cells in most rearing batches, the larvae were later confirmed as lecithotrophic (non-feeding) as (1) larvae were successfully reared until settlement without feeding, and (2) chlorophyll a fluorescence of C. gracilis was not incorporated into the larval intestine as observed under fluorescence microscopy. Auricularia larvae showed poor development of lateral arm protrusion and did not form hyaline spheres. Initial rearing densities under 0.4 larva mL−1 resulted in relatively good survival. Settling larvae were retrieved using polycarbonate corrugated sheets on which periphytic diatoms had been grown beforehand. Survival from hatching to 2 months after settlement was 1.0–1.8%, comparable with values reported for other sea cucumbers. Postsettled juveniles became orange-colored with black dorsal papillae in 50 days after settlement and subsequently gradually obtained a dark green-brown dorsal pigment. Juveniles having anal teeth and adult-like color pattern appeared from 4 months after settlement. Growth of the settled juveniles was 91.8 ± 1.5 μm day−1 from Jun to Dec, reaching 15.11 ± 5.63 mm long in 170 days, while the juveniles negatively grew during winter from Dec to Feb. The lecithotrophic short larval period of A. lecanora has potential for low-cost seed production, which is advantageous for development of aquaculture and restocking.

Gametogenesis and reproductive traits of the cold-seep mussel Gigantidas platifrons in the South China Sea

Gigantidas platifrons (Bivalvia, Mytilidae), the dominant species at the Formosa cold seep, relies on methanotrophic symbionts dwelling in its gills for nutrition. The reproductive patterns of G. platifrons provide fundamental information for understanding the population recruitment of this species. However, we know very little about important processes in reproduction, such as gametogenesis and symbiotic bacteria transmission. To this end, we described the developmental patterns of the gonads from nine surveys and juvenile length-distribution from one-year larval traps and detected bacteria in gonad from G. platifrons samples. Our results show that G. platifrons is a functionally dioecious species. The reproduction of G. platifrons is discontinuous, with spawning maturity peak around the fourth quarter of the year. The seasonal reproduction of G. platifrons was further supported by the unimodal shell length distribution of the trapped juvenile mussels. Given the small oocyte size (48.99–70.14 μm), which was comparable to that of coastal mussels, we proposed that G. platifrons developed via a free-living, planktotrophic larval stage before settlement. The blooms at the water surface can also supply the development of the planktonic larvae of G. platifrons. Meanwhile, no bacteria were observed in gonads, suggesting a horizontal symbiont transfer mode in this mussel. Collectively, these results provide fundamental biological information for an improved understanding of the early life history of G. platifrons in the Formosa cold seep.

Middle Triassic gastropods from the Besano Formation of Monte San Giorgio, Switzerland

For the first time gastropods from the Besano Formation (Anisian/Ladinian boundary) are documented. The material was collected from three different outcrops at Monte San Giorgio (Southern Alps, Ticino, Switzerland). The taxa here described are Worthenia (Humiliworthenia)? aff. microstriata, Frederikella cf. cancellata, ?Trachynerita sp., ?Omphaloptycha sp. 1 and ?Omphaloptycha sp. 2. They represent the best preserved specimens of a larger collection and document the presence in this formation of the clades Vetigastropoda, Neritimorpha and Caenogastropoda that were widespread on the Alpine Triassic carbonate platforms. True benthic molluscs are very rarely documented in the Besano Formation, which is interpreted as intra-platform basin sediments deposited in usually anoxic condition. Small and juvenile gastropods could have been lived as pseudoplankton attached to floating algae or as free-swimming veliger planktotrophic larval stages. Accumulations of larval specimens suggest unfavorable living conditions with prevailing disturbance in the planktic realm or mass mortality events. However, larger gastropods more probably were washed in with sediments disturbed by slumping and turbidite currents along the basin edge or storm activity across the platform of the time equivalent Middle San Salvatore Dolomite.

Food Restrictions Affect the Larval Metamorphosis and Early Juvenile Performance in a Neotropical Mangrove Fiddler Crab (Leptuca cumulanta).

Sporadic fluctuations in food availability may affect larval biology and post-metamorphic development in many marine invertebrates. In an experimental study in the laboratory, we investigated whether different regimes (1, 3, and 5 days) of initial starvation or feeding affect the survival and duration of the last planktotrophic larval stage (i.e., megalopa) of the neotropical mangrove fiddler crab Leptuca cumulanta. Newly metamorphosed crabs originating from megalopae starved for 1 and 3 days were cultured through the first 5 juvenile stages to further evaluate whether prior nutritional experience affects the post-larval performance of this species. All megalopae that were starved continuously died, while 80% of the larvae that were fed constantly metamorphosed successfully into the juvenile stage. Megalopae initially starved for 3 and 5 days exhibited lower survival (55% and 30% of larval metamorphosis, respectively) than larvae starved for only 1 day (85%) or fed constantly. The starvation periods (1, 3, and 5 days) also significantly prolonged the mean megalopal stage duration (12.8, 13.9, and 14.3 days, respectively) compared to the continuous feeding regime (10.6 days). Survival of the megalopae subjected to different periods of initial feeding (1, 3, and 5 days) was significantly lower (15.0%, 57.5%, and 62.5%, respectively) than survival of the larvae fed constantly. The mean megalopal stage duration, by contrast, did not vary among megalopae initially fed for 3 and 5 days or fed continuously (10.4 days). The larval starvation did not affect survival and carapace shape of juveniles, but it did alter their intermolt period, growth, and body size. These carryover effects were stronger in the first juvenile crab stage than in other juvenile stages. Our results indicate that the timing and duration of the starvation or feeding regime experienced by the megalopae may affect their successful survival and developmental period until metamorphosis to juvenile life. In addition, the preceding larval starvation associated with a prolonged larval period may also affect early juvenile performance in specific crab stages of L. cumulanta.

Molecular phylogeny, morphology, and distribution of Polygordius (Polychaeta: Polygordiidae) in the Atlantic and Mediterranean

Low morphological diversity among interstitial taxa makes it difficult to delimit species and their geographic boundaries based solely on morphology and molecular data often reveal cryptic species. Polygordius (Annelida, Polygordiidae) have low morphological diversity, but are unusual among interstitial species in their comparatively large size due to their elongated form, high fecundity, and potential for long-distance dispersal via a planktotrophic larval stage. Polygordius species collected from 14 localities in the Northwest Atlantic, Mediterranean Sea, and Southwest Atlantic including several of the respective type localities were analysed. This study presents the first phylogeny of the genus Polygordius and combines molecular data, sequences of COI, 16S and ITS1/2 genes, and morphological data for a systematic re-evaluation focusing on Atlantic species, with an emphasis on populations from European waters. Phylogenetic analyses recovered six valid species (P. appendiculatus, P. lacteus, P. neapolitanus, P. triestinus, P. jouinae, and P. eschaturus) and their distinctness is confirmed by haplotype network analyses. Thus, molecular data supported the validity of the previously recognized morpho-species and no new species were present. P. erythrophthalmus and P. villoti are invalid species being synonymous with P. lacteus. Subtle differences in head and pygidial morphology and larval type (endolarva vs. exolarva), were useful characters for discrimination. Yet seemingly significant variation in characters among individuals in some species was not diagnostic (e.g., number of pygidial cirri). Highly similar species based on adult morphology were shown to be sister taxa occurring in allopatry. Present day distribution patterns of species are summarized in light of this study.

Unexpected absence of island endemics: Long‐distance dispersal in higher latitude sub‐Antarctic Siphonaria (Gastropoda: Euthyneura) species

AbstractAimWe assess biogeographical patterns, population structure and the range of species in the pulmonate genus Siphonaria across the sub‐Antarctic. We hypothesized that locally endemic cryptic species will be found across the distribution of these direct‐developing limpets in the sub‐Antarctic.LocationThe sub‐Antarctic coasts of the Southern Ocean including South America, the Falkland/Malvinas, South Georgia, Kerguelen and Macquarie Islands.MethodsMulti‐locus phylogenetic reconstructions, mtDNA time‐calibrated divergence time estimations and population‐based analyses of Siphonaria populations were used at the scale of the Southern Ocean.ResultsWe resolve two widely distributed lineages of Siphonaria (S. lateralis and S. fuegiensis) across the sub‐Antarctic. MtDNA divergence time estimates suggest that they were separated around 4.0 Ma (3.0 to 8.0 Ma). Subsequently both species followed different evolutionary pathways across their distributions. Low levels of genetic diversity characterize the populations of both species, reflecting the role of Quaternary glacial cycles during their respective demographic histories, suggesting high levels of dispersal among geographically distant localities.Main conclusionsSiphonaria lateralis and S. fuegiensis constitute sister and broadly co‐distributed species across the sub‐Antarctic. Unexpected transoceanic similarities and low levels of genetic diversity in both these direct‐developing species imply recurrent recolonization processes through long‐distance dispersal to isolated sub‐Antarctic islands. For such groups of Southern Ocean invertebrates, rafting may be more effective for long‐distance dispersal than a free‐living planktotrophic larval stage. This biogeographical model may explain why many marine species lacking a dispersal phase exhibit broad distributions, low genetic diversity and low population structure over thousands of kilometres.

Ecology of the spider crab Libinia ferreirae (Brachyura: Majoidea): ontogenetic shifts in habitat use

We described the ecology of the spider crab Libinia ferreirae testing the habitat segregation during the ontogenetic shifts. Collections were performed monthly by trawling along the coastal area of Cananeia, Sao Paulo State (southeastern Brazil). Medusae were examined for the presence of any symbionts, and crabs were classified as juveniles (abdomen sealed to the sternite), adults (unsealed abdomen), and ovigerous females (embryos adhered to the pleopods). The environmental factors related to the water column were obtained using a multiparameter probe. In total, 564 adults and 357 juveniles were collected. However, all juveniles were obtained in association with Lychnorhiza lucerna medusae. An increase in the abundance of ovigerous females was observed as chlorophyll levels (phytoplanktonic production) increased, which is consistent with the patterns proposed for crustaceans with planktotrophic larval stages, i.e., the association of larval hatching with oceanic productivity could explain the success in juvenile recruitment approximately two months after the peak in the abundance of ovigerous females (cross-correlation: r = 0.96). This spider crab shows an ecological strategy of habitat segregation among juvenile and adult individuals, thus avoiding competition for resources among different life cycle stages.

A silicified Early Triassic marine assemblage from Svalbard

Understanding how the marine biosphere recovered from the late Permian mass extinction event is a major evolutionary question. The quality of the global fossil record of this interval is, however, somewhat poor due to preservational, collection and sampling biases. Here we report a new earliest Induan (Hindeodus parvus Zone) marine assemblage from the Deltadalen Member of the Vikinghøgda Formation, central Spitsbergen, which fills a critical gap in knowledge. The fully silicified fossils comprise the oldest silicified assemblage known from the Triassic and provide critical new systematic data. For its age, the assemblage is exceptionally diverse with 14 species of bivalves and gastropods, as well as conodonts and ammonoids. Four new bivalve species (Austrotindaria antiqua, A. svalbardensis, Nucinella taylori and N. nakremi) and one new gastropod species (Glabrocingulum parvum) are described, and five families are recorded in the Induan for the first time. Some of the common and globally widespread Early Triassic taxa, such as Unionites, are also present, and their exceptional preservation reveals key morphological characters that are documented for the first time. Taxonomic and ecological revisions based on these new data suggest that shallow-infaunal deposit-feeders were a dominant component of pre-Spathian benthic communities. The gastropods and bivalves all possessed a planktotrophic larval stage, which may have been a particular advantage in the wake of the late Permian mass extinction.http://zoobank.org/urn:lsid:zoobank.org:pub:3EBCAEF3-27C2-4216-9F18-89F195FA534F

Ocean currents determine functional connectivity in an Antarctic deep‐sea shrimp

AbstractThe coherency among larval stages of marine taxa, ocean currents and population connectivity is still subject to discussion. A common view is that organisms with pelagic larval stages have higher dispersal abilities and therefore show a relatively homogeneous population genetic structure. Contrary to this, local genetic differentiation is assumed for many benthic direct developers. Specific larval or adult migratory behavior and hydrographic effects may significantly influence distribution patterns, rather than passive drifting abilities alone. The Southern Ocean is an ideal environment to test for the effects of ocean currents on population connectivity as it is characterized by several well‐defined and strong isolating current systems. In this study we studied the genetic structure of the decapod deep‐sea shrimp Nematocarcinus lanceopes, which has planktotrophic larval stages. We analysed 194 individuals from different sample localities around the Antarctic continent using nine microsatellite markers. Consistent with a previous study based on mitochondrial DNA markers, primarily weak genetic patterns among N. lanceopes populations around the continent were found. Using ocean resistance modeling approaches we were able to show that subtle genetic differences among populations are more likely explained by ocean currents rather than by geographic distance for the Atlantic Sector of the Southern Ocean.

New Occurrence of Abnormal Sea Star, Astropecten indicus from Mudasalodai, South East Coast of India

A marine invertebrate of starfish is a most familiar one. It was mainly occur on the seabed and diversity of starfish is remarkable ones. Astropecten sp is not easily identified organism while a number of species a long-lived planktotrophic larval stage. As a rule of pentamerism, Astropecten indicus strictly produces only 5 arms but some time the number was lesser than or greater than five and shows its abnormality. The reason may be of regeneration of plate systems which is responsible for forming the whole organs during larval metamorphosis or regenerating the lost plate systems in the disc in the later stages or due to environmental factors or may be of mutation.

Earliest ontogeny of Early Palaeozoic Craniiformea: compelling evidence for lecithotrophy

Popov, L.E., Bassett, M.G. & Holmer, L.E. 2012: Earliest ontogeny of Early Palaeozoic Craniiformea: compelling evidence for lecithotrophy. Lethaia, Vol. 45, pp. 566–573. The early ontogeny of Palaeozoic Craniiformea (Brachiopoda) remains controversial, with conflicting reports of evidence indicating lecithotrophic versus planktotrophic larval stages. Further compelling evidence for lecithotrophy in Palaeozoic craniiforms is described here. Newly obtained, well-preserved Silurian specimens of craniiforms, including Craniops (Craniopsida), and Lepidocrania? and Orthisocrania (Craniida) from Gotland and the St. Petersburg region, form the basis for this study. The new material demonstrates that the characters of shell structure and shell formation provide evidence of early differentiation of an adult dorsal mantle, and the presence of a distinctive primary layer with a characteristic lath-like pattern indicates that these craniiforms underwent a lecithotrophic larval stage, more or less identical to that of living. □Novocrania. Brachiopoda, Craniiformea, ontogeny, phylogeny, Early Palaeozoic.

Fussy feeders: phyllosoma larvae of the Western Rocklobster (Panulirus cygnus) demonstrate prey preference.

The Western Rocklobster (Panulirus cygnus) is the most valuable single species fishery in Australia and the largest single country spiny lobster fishery in the world. In recent years a well-known relationship between oceanographic conditions and lobster recruitment has become uncoupled, with significantly lower recruitment than expected, generating interest in the factors influencing survival and development of the planktonic larval stages. The nutritional requirements and wild prey of the planktotrophic larval stage (phyllosoma) of P. cygnus were previously unknown, hampering both management and aquaculture efforts for this species. Ship-board feeding trials of wild-caught mid-late stage P. cygnus phyllosoma in the eastern Indian Ocean, off the coast of Western Australia, were conducted in July 2010 and August-September 2011. In a series of experiments, phyllosoma were fed single and mixed species diets of relatively abundant potential prey items (chaetognaths, salps, and krill). Chaetognaths were consumed in 2–8 times higher numbers than the other prey, and the rate of consumption of chaetognaths increased with increasing concentration of prey. The highly variable lipid content of the phyllosoma, and the fatty acid profiles of the phyllosoma and chaetognaths, indicated they were from an oligotrophic oceanic food chain where food resources for macrozooplankton were likely to be constrained. Phyllosoma fed chaetognaths over 6 days showed significant changes in some fatty acids and tended to accumulate lipid, indicating an improvement in overall nutritional condition. The discovery of a preferred prey for P. cygnus will provide a basis for future oceanographic, management and aquaculture research for this economically and ecologically valuable species.

Reproductive Traits of the Cold-Seep Symbiotic Mussel Idas modiolaeformis: Gametogenesis and Larval Biology

We describe the first reproductive features of a chemosynthetic mussel collected at cold seeps from the eastern Mediterranean Sea. Idas modiolaeformis (Bivalvia, Mytilidae) is a hermaphroditic species in which production of male and female gametes likely alternates, a feature regarded as an adaptation to patchy and ephemeral habitats. By using fluorescent in situ hybridization, we demonstrate that bacterial symbionts, while present within the gills, are absent within acini that enclose female gametes and male gametes. This supports the hypothesis of environmental acquisition of symbionts in chemosynthetic mytilids. Prodissoconch I (PI) is relatively small compared to prodissoconch II (PII), suggesting a planktotrophic larval stage. Diameters of the two larval shells are in the range of sizes reported for mytilids, with a PII size between that of the shallow Mytilus edulis and that of the cold-seep mussel "Bathymodiolus" childressi.

The Long and Short of It: Genetic Variation and Population Structure of the Anchialine Atyid Shrimp Caridina rubella on Miyako-jima, Japan

One of the most threatened ecosystems on many islands may be anchialine habitats, or coastal land-locked water bodies with no surface connection to the sea yet containing brackish water that fluctuates with the tides. To better manage these habitats, it is important to develop a broader understanding of the biodiversity within them since such knowledge plays critical roles in establishing conservation strategies. In this study, the genetic variation and population structure of an anchialine atyid shrimp, Caridina rubella Fujino and Shokita, 1975 was investigated in the Southern Ryukyu Archipelago, Japan. Given a planktotrophic larval stage and its potential amphidromous life cycle, populations of C. rubella on the island of Miyako-jima (to which it is apparently restricted) were hypothesized to have little to no structure across the island. To test this, 61 individuals were collected from four anchialine caves and sequence variation examined at the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA). Surprisingly, significant genetic structure was exhibited across distances ranging from 10 km. Additionally, deep (∼17% p-distance) genetic divergence correlating with distinct variation in rostrum lengths was found between closely situated, but more-or-less completely isolated, populations. This implies “C. rubella ”m ay actually represent two distinct species on Miyako-jima. Given that this atyid is already listed as a threatened species by the Japanese government, the results presented here are useful in the formulation and implementation of future conservation plans for populations of C. rubella on Miyako-jima.

Fluctuations of the oxygen minimum zone at the end of Oceanic Anoxic Event 2 reflected by benthic and planktic fossils

The latest Cenomanian to early Turonian (Late Cretaceous) section at Vallecillo, Mexico, contains a continuous and highly fossiliferous sedimentary record across the late Oceanic Anoxic Event (OAE) 2, and shows similar distributions of benthic inoceramids and planktic foraminifers during this period of an expanded oxygen minimum zone (OMZ). We suggest that these synchronous abundance changes result from similar environmental vulnerability of planktotrophic larval stages of inoceramids and deeper-dwelling planktic foraminifers, and that these synchronous changes reflect the expansion of the OMZ. The abundances of ammonites and fishes, used as independent control groups, do not correlate and rule out a preservational bias. Ammonites, fishes, and their hatchlings thus populated shallower water depths than inoceramid gametes and planktic foramininifers. The improving conditions at the end of OAE 2 resulted in the dispersal of new inoceramid and foraminiferal morphotypes.

A revision of the Australian fossil species of Zoila (Gastropoda: Cypraeidae)

Darragh, Thomas A. 2011. A revision of the Australian fossil species of Zoila (Gastropoda: Cypraeidae). Memoirs of Museum Victoria 68: 1–28. Zoila Jousseaume, 1884 is a cowry genus, the species of which are now confined to the coastal waters of Western Australia and southern Australia. Six fossil species are known from southeast Australia, of which three are new, ranging in age from late Oligocene to middle Miocene, known from the Murray, Otway and Bass basins. Three fossil species are known from Western Australia, of which three are new, ranging in age from late Eocene to late Pliocene, known from the Carnarvon, Bremer and Eucla basins. Umbilia (Gigantocypraea) Schilder 1927 (type species Cypraea gigas McCoy) is regarded as a synonym of Zoila. The earliest record of the genus is Z. chathamensis (Cernohorsky, 1971), Paleocene/early Eocene, Chatham Islands, probably ancestral to the Australian fossils. Zoila is closely related to Cypraeorbis Conrad, 1865, of which Bernaya Jousseaume, 1884 is regarded as a synonym. Living species are known to have no planktotrophic larval stage, so there is considerable variation in species morphology. Such direct development arose in these cowries at least as early as the late Eocene. Fossils described here are Zoila viathomsoni sp. nov., Z. didymorhyncha sp. nov., Z. glomerabilis sp. nov., Z. dolichorhyncha sp. nov., Z. mulderi (Tate, 1892), Z. platypyga (McCoy, 1876) (= consobrina McCoy, toxorhyncha Tate, platypyga simplicior Schilder), Z. gigas (McCoy, 1867) (= dorsata, gabrieli), Z. campestris n. sp. and Z. fodinata n. sp.

Phylogenetic relationships in the genus Astropecten Gray (Paxillosida: Astropectinidae) on a global scale: molecular evidence for morphological convergence, species-complexes and possible cryptic speciation

With over 150 described species, Astropecten Gray (Paxillosida:Astropectinidae) is one of the most species-rich genera among sea stars. This diversity is remarkable, because most species of Astropecten have a long-lived planktotrophic larval stage, which would be expected to lead to a low speciation rate. The taxonomy of this genus is complex and not well resolved, and phylogenetic relationships have only been addressed in the beginning of the last century. In order to resolve general taxonomic issues, identify speciation patterns and estimate species diversity within the genus Astropecten, we inferred a molecular phylogeny of 117 specimens of Astropecten belonging to 40 species from around the world using mitochondrial DNA (mtDNA) sequences of 12S rRNA, 16S rRNA and cytochrome oxidase subunit I (COI). We compared the resulting molecular phylogeny to a previously published morphological one by Döderlein and investigated the possibility of morphological convergence in species from different geographic regions. Finally, we also aimed at identifying potentially problematic descriptions and/or signs of cryptic speciation in Astropecten. The global molecular phylogeny exhibited three main clades, each containing specimens of the same geographic region: 1. the IndoPacific; 2. the Neotropics; and 3. the eastern Atlantic and Mediterranean. Phylogenetic inferences based on mtDNA indicate that morphological and ecological convergence has taken place in Astropecten, resulting in allopatric non-sister taxa with similar morphologies and habitat preferences. The comparison to Döderlein’s morphological phylogeny reveals congruence on the whole but many discrepancies on a local scale, indicating that meaningful morphological characters are not easily identified and categorized in Astropecten. Our results also reveal that A. polyacanthus Müller & Tröschel and A. indicus Döderlein are species-complexes; cryptic speciation may have occurred within each of these morphospecies. Furthermore, several variants, previously presumed to be conspecific, exhibit genetic distances large enough to justify recognizing them as separate species.

Reproduction of the vermetid gastropod Dendropoma maximum (Sowerby, 1825) in Moorea, French Polynesia

Vermetidae are sessile molluscs with tubular shells cemented to the substrate. Although they are common inhabitants of coral reefs and rocky shores, little is known about the basic biology of most species. Dendropoma maximum is the largest vermetid species and is common across its Indo-Pacific range. Here we report on a study of reproductive and morphological traits in D. maximum from the lagoon around Moorea, French Polynesia. Both body length and diameter of shell aperture (generally the only visible part of the animal in the field) were good predictors of body weight and this relationship did not differ between males and females. Shell apertural diameter is therefore a good index of body size in D. maximum. The sex ratio became increasingly dominated by females with increasing body size, which is suggestive of protandric hermaphroditism. Probability of brooding, the number and size of brooded egg capsules, and the number of embryos per capsule were all positively related to female size. Females released veliger larvae that lived without additional food for up to 10 days, but were observed to feed when offered cultured phytoplankton on the final day. This is the first direct observation of feeding by larvae in this genus, and a planktotrophic larval stage has implications for potential dispersal in D. maximum.

Spatial and temporal population genetic structure of four northeastern Pacific littorinid gastropods: the effect of mode of larval development on variation at one mitochondrial and two nuclear DNA markers

We investigated the effect of development mode on the spatial and temporal population genetic structure of four littorinid gastropod species. Snails were collected from the same three sites on the west coast of Vancouver Island, Canada in 1997 and again in 2007. DNA sequences were obtained for one mitochondrial gene, cytochrome b (Cyt b), and for up to two nuclear genes, heat shock cognate 70 (HSC70) and aminopeptidase N intron (APN54). We found that the mean level of genetic diversity and long-term effective population sizes (N(e)) were significantly greater for two species, Littorina scutulata and L. plena, that had a planktotrophic larval stage than for two species, Littorina sitkana and L. subrotundata, that laid benthic egg masses which hatched directly into crawl-away juveniles. Predictably, two poorly dispersing species, L. sitkana and L. subrotundata, showed significant spatial genetic structure at an 11- to 65-km geographical scale that was not observed in the two planktotrophic species. Conversely, the two planktotrophic species had more temporal genetic structure over a 10-year interval than did the two direct-developing species and showed highly significant temporal structure for spatially pooled samples. The greater temporal genetic variation of the two planktotrophic species may have been caused by their high fecundity, high larval dispersal, and low but spatially correlated early survivorship. The sweepstakes-like reproductive success of the planktotrophic species could allow a few related females to populate hundreds of kilometres of coastline and may explain their substantially larger temporal genetic variance but lower spatial genetic variance relative to the direct-developing species.