Holoplanktonic Gastropods Research Articles

Between sea angels and butterflies: A global phylogeny of pelagic pteropod molluscs

Pteropods, holoplanktonic gastropods, play pivotal roles in marine ecosystems as integral components of food webs and carbon cycling. With global change threatening pelagic ecosystem equilibrium, conserving pteropod biodiversity is paramount. Here, we present the most extensive phylogenetic study of the order Pteropoda to date, utilizing a complete mitogenome phylogeny to support the suppression of Thecosomata, thus demonstrating the lack of relationship between Pseudothecosomata and Euthecosomata. Through multilocus Sanger-based taxon sampling with 411 specimens (92 newly sequenced), representing nearly 100 species (out of 163 valid) from various oceans, we elucidate robust support for higher taxonomic rankings. Despite strong support, relationships between the major groups Gymnosomata, Pseudothecosomata, and Euthecosomata remain contentious. Our study addresses unresolved taxonomic questions, identifying cryptic species complexes across vast biogeographic areas, and offering unprecedented insights into pteropod diversity. We shed light on several open questions in pteropod systematics, proposing the reclassification of L. antarctica stat. rest. and elucidating the position of Thliptodon, Heliconoididae, and Thieleidae. This systematic review enhances our understanding of pteropod diversity and underscores the urgency of conservation efforts in the face of changing oceanic conditions.

The middle miocene (Badenian) holoplanktonic mollusks (Euthecosomata - Pteropoda) from Serbia, central paratethys

The present paper deals with holoplanktonic gastropods (Pteropoda) from the Middle Miocene (Badenian) deposits of Serbia. The material for the present study comes from three localities at the southern margin of the Pannonian Basin (Central Paratethys): Konjarnik (greater center of Belgra de), Sumijevac stream near Koceljeva (western Serbia), and Radljevo (Kolubara Basin, central Serbia). A total of four taxa were recorded and their stratigraphic value is discussed. Two taxa were identified to species level: Vaginella austriaca KITTL, 1886, belonging to the family Cavoliniidae GRAY, 1850 (1815), and Limacina valvatina (REUSS, 1867)?, from the family Limacinidae GRAY, 1847. Four specimens could only be identified to genus level (Vaginella sp. indet. and Clio? sp. indet.). The specimen of Clio? sp. indet. is possibly the first find of the genus Clio in Serbia. Here presented records of the genera Vaginella and Clio? from the late Badenian (NN6 nannozone) modify the insight into their paleogeographical distribution in the Middle Miocene of the Central Paratethys.

Calcification depth of pteropods in the Coral Sea using stable oxygen isotopes

Pteropods are marine holoplanktonic gastropods inhabiting epipelagic and mesopelagic waters with a wide distribution from tropical to polar regions. However, their ontogeny and calcification depth/habitat depth are not well understood. To this end, we analyzed the stable oxygen isotopic composition of five pteropod species (Diacavolinia angulata, Diacavolinia longirostris, Heliconoides inflatus, Limacina bulimoides and Telodiacria quadridentata) from two multicores recovered offshore north-eastern Australia between 15°S and 26°S in the Coral Sea. We applied the Limacina dissolution index (LDX) to evaluate the preservation status of the pteropods, which revealed very good to moderate aragonite preservation at both locations. Comparison of the pteropod shell oxygen isotopic composition with predicted aragonite equilibrium oxygen isotope values implies calcification depths of 50 ± 20 m for D. longirostris and 75 ± 30 m for D. angulata, suggesting that they predominantly calcify in the mixed layer during austral summer. The apparent calcification depths of T. quadridentata and H. inflatus at 90 ± 30 m and 120 ± 30 m at both sites indicate a year-round, lower mixed layer and upper thermocline habitat depth, respectively, while T. quadridentata appear to calcify at temperatures above 22 °C. The calcification depth of L. bulimoides is deeper (100 ± 15 m) at the northern station and shallower (75 ± 30 m) at the southern station that might also hint to a temperature control. The relative narrow calcification depth ranges of the investigated pteropod species in the Coral Sea bolster their potential for reconstructing past ocean conditions at the mixed layer and thermocline.

Stack of cellular lamellae forms a silvered cortex to conceal the opaque organ in a transparent gastropod in epipelagic habitat.

Gelatinous zooplankton in epipelagic environments often have highly transparent bodies to avoid detection by their visual predators and prey; however, the digestive systems are often exceptionally opaque even in these organisms. In a holoplanktonic gastropod, Pterotrachea coronata, the visceral nucleus is an opaque organ located at the posterior end of its alimentary system, but this organ has a mirrored surface to conceal its internal opaque tissue. Our ultrastructural observation proved that the cortex of the visceral nucleus comprised a stack of thin cellular lamellae forming a Bragg reflector, and the thickness of lamellae (0.16 µm in average) and the spaces between the lamellae (0.1 µm in average) tended to become thinner toward inner lamellae. Based on the measured values, we built virtual models of the multilamellar layer comprising 50 lamellae and spaces, and the light reflection on the models was calculated using rigorous coupled wave analysis to evaluate their properties as reflectors. Our simulation supported the idea that the layer is a reflective tissue, and the thickness of the lamella/space must be chirped to reflect sunlight as white/silver light, mostly independent of the angle of incidence. In P. coronata, the cortex of the visceral nucleus comprised multicellular lamellae that form a chirped Bragg reflector. It is distinct in structure from the intracellular Bragg structures of common iridophores. This novel Bragg reflector demonstrates the diversity and convergent evolution of reflective tissue using reflectin-like proteins in Mollusca.

Ecological adaptation of marine floras and faunas across the Early Jurassic Toarcian Oceanic Anoxic Event – A case study from northern Germany

We present new, high resolution bio- and chemostratigraphic data (calcareous nannofossils, ammonites, δ13Corg) of the lower Toarcian from an outcrop (Hondelage) in northern Germany. The three data sets, which cover lithostratigraphically the uppermost Amaltheenton-Formation (upper Pliensbachian) and the lower part of the Posidonienschiefer-Formation (lower Toarcian), allow a calibration of the different stratigraphic schemes in ultra high resolution. They further shed light on the ecologic conditions controlling the assemblage composition and evolutionary patterns of calcareous nannofossils, ammonites and gastropods.The distinctive negative δ13Corg excursion (negative CIE, Jenkyns Event), which is part of the early Toarcian Oceanic Anoxic Event (T-OAE), falls lithostratigraphically into the lower part of the laminated black shales of the Posidonienschiefer facies. The lower part of the Jenkyns Event is marked by the first occurrences of the calcareous nannofossil species Carinolithus superbus crassus and Diductius constans. These two events are biostratigraphically assigned to the Tiltoniceras antiquum ammonite Biohorizon (uppermost Dactylioceras tenuicostatum ammonite Zone). The top of the Jenkyns Event has been assigned to the Cleviceras exaratum ammonite Biohorizon (Harpoceras serpentinum ammonite Zone) of the lower Toarcian. The last occurrence of the nannofossil species Biscutum grande lies in the middle part of the Jenkyns Event.Calcareous nannofossils, ammonite faunas and gastropods are discussed with respect to the environmental and climatic changes, which occurred across the Pliensbachian/Toarcian boundary interval and throughout the Jenkyns Event. The extreme impoverished nannofossil and ammonite assemblages of the uppermost Pliensbachian are interpreted in the context of a cooling, primarily affecting the calcareous shelled primary producers. The onset of the Jenkyns Event in the lower Toarcian post-dates this cooling and is related to a subsequent warming. This climatic shift caused a bloom of diverse opportunistic nannofossil and ammonite taxa in the lower Toarcian. Nannofossil abundance patterns were controlled by an increased nutrient availability. The rapid evolution of the ammonite genera Tiltoniceras, Eleganticeras and Cleviceras (family Hildoceratidae), which started in the lower part of the Jenkyns Event, is potentially related to their adaptation to a shallow water dwelling habitat. The mass occurrence of phylogenetically first holoplanktonic gastropods in the lower part of the Jenkyns Event is interpreted in the context of impoverished ocean water oxygenation, which in turn triggered the evolution of a new ecological strategy.

Transcriptomic Responses of Adult Versus Juvenile Atlantids to Ocean Acidification

Shelled holoplanktonic gastropods are among the most vulnerable calcifiers to ocean acidification. They inhabit the pelagic environment and build thin and transparent shells of aragonite, a metastable form of calcium carbonate. While shelled pteropods have received considerable attention and are widely regarded as bioindicators of ocean acidification, atlantids have been much less studied. In the open ocean, atlantids are uniquely positioned to address the effects of ocean acidification at distinct trophic levels. From juvenile to adult, they undergo dramatic metamorphosis. As adults they are predatory, feeding primarily on shelled pteropods, copepods and other zooplankton, while as juveniles they feed on algae. Here we investigated the transcriptome and the impact of a three-day CO2 exposure on the gene expression of adults of the atlantid Atlanta ariejansseni and compared these to results previously obtained from juveniles. Individuals were sampled in the Southern Subtropical Convergence Zone (Atlantic Ocean) and exposed to ocean chemistry simulating past (~mid-1960s), present (ambient) and future (2050) conditions. In adults we found that the changes in seawater chemistry had significantly affected the expression of genes involved in biomineralization and the immune response, although there were no significant differences in shell growth between the three conditions. In contrast, juveniles experienced substantial changes in shell growth and a broader transcriptomic response. In adults, 1170 genes had the same direction of expression in the past and future treatments when compared to the ambient. Overall, this type of response was more common in adults (8.6% of all the genes) than in juveniles (3.9%), whereas a linear response with decreasing pH was more common in juveniles (7.7%) than in adults (4.5%). Taken together, these results suggest that juveniles are more sensitive to increased acidification than adults. However, experimental limitations including short incubation times, one carboy used for each treatment and two replicates for transcriptome analysis, require us to be cautious about these conclusions. We show that distinct transcriptome profiles characterize the two life stages, with less than 50% of shared transcripts. This study provides an initial framework to understand how ocean acidification may affect the molecular and calcification responses of adult and juvenile atlantids.

Spatio-temporal variability of the zooplankton community in the SW Mediterranean 1992–2020: Linkages with environmental drivers

Variability in the spatial and temporal distribution of the mesozooplankton abundance in the N Alboran Sea (SW Mediterranean) was assessed intermittently from 2010 to 2020, and compared with 1992–2000 historical time series data. Total abundance of mesozooplankton was significantly higher in the coast than in the shelf and slope waters. There were significant differences in mesozooplankton abundance between 1992–2000 and 2010–2020 at the three zones. Copepods dominated the mesozooplankton during winter and spring, but cladocerans and doliolids also became important components of the community in summer and autumn. We found significant increases between the first and the second decadal periods in the abundance of copepods, appendicularians, holoplanktonic gastropods and siphonophores in the shelf. However, in the coast, copepod nauplii, doliolids, gastropods and siphonophores increased, while euphausiids abundance decreased significantly. These trends contrast with the ongoing decline of the sardine stocks in European waters. Increasing temperature and decreasing predation pressure are suggested to be the main drivers of mesozooplankton variability.

Evidence that host ecology drives first intermediate host use in the Didymozoidae (Trematoda: Hemiuroidea): an asexual infection in a vermetid (Gastropoda).

The Didymozoidae (Trematoda: Hemiuroidea) is among the most speciose trematode families, known from a wide range of marine teleost fishes. Despite their richness, however, didymozoid life cycles are unusually poorly known; only two first intermediate hosts are known, a marine bivalve (Anadara trapezia) and a pelagic gastropod (Firoloida desmarestia). This study uses multi-locus molecular sequence data to identify a novel first intermediate host for the family, a sessile gastropod of the genus Thylacodes Guettard (Vermetidae). The didymozoid infection is not identified to species but, based on molecular phylogenetic analyses, it is close to Saccularina magnacetabula Louvard et al., 2022, which uses a bivalve as a first intermediate host. The distribution of known first intermediate hosts of didymozoids (a bivalve, a holoplanktonic gastropod and a sessile gastropod that feeds with the use of mucus nets) suggests that first intermediate host use within the Didymozoidae has been opportunistically driven by the trophic ecology of potential mollusc hosts and has involved significant host-switching events.

Distribution and abundance of planktonic mollusks along a longitudinal gradient in the Southeastern Pacific off Chile

The objectives of this research were to estimate the abundance of the main groups of planktonic mollusks (meroplanktonic larvae, holoplanktonic gastropods and cephalopod paralarvae), and relate these groups to the physical-chemical water properties along a longitudinal gradient between Caldera, on the coast of mainland Chile, and the Easter Island ecoregion (Rapa Nui Island and Salas y Gómez Island), in the Southeast Pacific Ocean. Plankton samples were collected over the course of the CIMAR 21-Islas Cruise, from October to November 2015, at 33 oceanographic stations via vertical hauls of a WP2 net (180-µm mesh size) from a maximum depth of 300 m to the sea surface. Mollusks were sorted, counted and initially assigned to Class rank, later being identified to lower taxonomic ranks. Planktonic mollusks were obtained at all stations, and were composed of 92.7% of Gastropoda and 7.3% of Bivalvia. The total abundance of mollusks varied between 55 and 4,922 individuals 100 m-3.Euthecosomate gastropods exhibited the highest occurrence within the oceanic area. Meanwhile, no paralarvae were captured. Differences in the composition of planktonic mollusks between the continental and oceanic zones were evident. Bivalve larvae increased their abundance in warmer, salty and vertically mixed waters. These results are the first record of meroplanktonic mollusks in waters near the Chilean oceanic islands, and suggest that planktonic mollusks display spatial variation at the scale of the South Pacific Basin, which could be related to the hydrographic conditions and the water column structure.

Palaeoceanographic significance of aragonitic pteropods in the Indian Ocean – a review

The Quaternary pteropod records published in the late 1990s from the Indian Ocean provided vital information on past oceanographic and climatic changes in this region. This paper reviews the published work on pteropod preservation and abundance in the Indian Ocean to evaluate the usefulness of this microfossil group in palaeoceanographic reconstructions. Their aragonitic shell chemistry makes them reliable indicators of ocean acidification, paleaoceanography and paleoclimate. An increased interest in studying this faunal group has arisen from recent findings on the vulnerability of aragonite shell preservation to human impacted water column chemistry changes. The compiled pteropod studies show that most of the pteropod databases contain information on abundance and distribution. However, the biogeochemical parameters and processes, such as aragonite production in the water column, their settling fluxes and the shell dissolution patterns are less explored. Despite the wide geographical range of pteropods and their significance in the marine food web, the ecology and taxonomy of the holoplanktonic gastropods in the Indian Ocean are poorly known. Though these pteropods are recovered in plankton tows (standing crop) and sediment traps (settling fluxes), the surface sediments in large parts of the northern Indian Ocean are completely devoid of them. Thus, assessing their fate in the water column and the sediment–water interface and their response to prevailing biogeochemical conditions are worth pursuing. Genomic studies and isotopic and elemental chemistry of living and fossil pteropods could help assess their response to ecological changes. To date, such modern techniques have been little utilized in studying Indian Ocean pteropods. A knowledge of their shell chemistry is crucial in the context of increased input of anthropogenic CO2 and the susceptibility of pteropod preservation to changing climate.

Oceanic dispersal barriers in a holoplanktonic gastropod.

Pteropods, a group of holoplanktonic gastropods, are regarded as bioindicators of the effects of ocean acidification on open ocean ecosystems, because their thin aragonitic shells are susceptible to dissolution. While there have been recent efforts to address their capacity for physiological acclimation, it is also important to gain predictive understanding of their ability to adapt to future ocean conditions. However, little is known about the levels of genetic variation and large‐scale population structuring of pteropods, key characteristics enabling local adaptation. We examined the spatial distribution of genetic diversity in the mitochondrial cytochrome c oxidase I (COI) and nuclear 28S gene fragments, as well as shell shape variation, across a latitudinal transect in the Atlantic Ocean (35°N–36°S) for the pteropod Limacina bulimoides. We observed high levels of genetic variability (COI π = 0.034, 28S π = 0.0021) and strong spatial structuring (COI ΦST = 0.230, 28S ΦST = 0.255) across this transect. Based on the congruence of mitochondrial and nuclear differentiation, as well as differences in shell shape, we identified a primary dispersal barrier in the southern Atlantic subtropical gyre (15–18°S). This barrier is maintained despite the presence of expatriates, a gyral current system, and in the absence of any distinct oceanographic gradients in this region, suggesting that reproductive isolation between these populations must be strong. A secondary dispersal barrier supported only by 28S pairwise ΦST comparisons was identified in the equatorial upwelling region (between 15°N and 4°S), which is concordant with barriers observed in other zooplankton species. Both oceanic dispersal barriers were congruent with regions of low abundance reported for a similar basin‐scale transect that was sampled 2 years later. Our finding supports the hypothesis that low abundance indicates areas of suboptimal habitat that result in barriers to gene flow in widely distributed zooplankton species. Such species may in fact consist of several populations or (sub)species that are adapted to local environmental conditions, limiting their potential for adaptive responses to ocean changes. Future analyses of genome‐wide diversity in pteropods could provide further insight into the strength, formation and maintenance of oceanic dispersal barriers.

Freboldia carinii sp. nov. from the Middle Triassic Brembana Valley (Esino Limestone, Southern Alps, Italy) – possibly the oldest known holoplanktonic gastropod

A monospecific mass occurrence of the new gastropod species Freboldia carinii sp. nov. is described from the Middle Triassic Esino Limestone of the Brembana Valley, Southern Alps, Italy. It is the second species assigned to the genus Freboldia that was initially described from the Early Jurassic of Ellesmere Island, Canadian Arctic. This gastropod is unusual in being planispiral and inflated with a nearly bilateral symmetrical shape and in having a very thin shell. Like the Canadian type species of Freboldia, the new Triassic species is interpreted as a possibly holoplanktonic gastropod. If true, it would be the oldest known example of this life style in Gastropoda.

Some observations on the geological history of the holoplanktonic gastropods

The pteropods (sea butterflies) and heteropods (sea elephants) are two groups of holoplanktonic gastropods that are important components of the modern, open ocean, plankton. The geological record of the pteropods (Pteropoda) and heteropods (Pterotracheoidea) extends to at least the earliest Eocene (55 million years ago), although there are records of taxa in the earliest Jurassic and mid-Late Cretaceous that may be planktonic gastropods. The more complete fossil record of pteropods and heteropods begins in the early Paleogene, coinciding with the transition from a calcitic ocean to an aragonitic ocean and it is possible that these aragonitic gastropods either appeared at that time or certainly commenced their wider diversification. While known diversity or species richness are subject to taxonomic ‘distortion’, especially when comparing biological data with palaeobiological data, pteropod and heteropod diversity appears to have been affected by changes in global climate. The heteropods may have been the product of our modern, thermohaline-driven ocean, while the pteropods diversified during the hyperthermal events of the early to mid-Eocene but also survived the transition to the modern, thermohaline-driven ocean and the onset of the present ‘icehouse world’.

Distribution of Atlantidae species (Gastropoda: Pterotracheoidea) during an El Niño event in the Southern California Current System (summer-fall 2015)

Atlantids are holoplanktonic gastropods present in tropical to sub-polar waters, and have gained an increasing interest due to their potential use as biological indicators of climate change and ocean acidification. However, there is a lack of information regarding their distribution for large areas of some oceans, particularly in the California Current System (CCS), which has been used as a model for many acidification studies and where intense warming events occur. The distribution patterns of 18 species of Atlantidae off the west coast of the Baja California Peninsula, Mexico, representing 90% of the atlantid species registered for the Pacific Ocean, were analyzed during a period of warm anomalies associated with the El Niño of 2015-2016 and the 2014-2016 marine heat wave (MHW). The species distribution showed 3 groups: 2 in the north (coastal and oceanic) and 1 in the south. The limit of distribution between these 3 groups was found in the vicinity of Punta Eugenia (PE). The southernmost community of atlantids was characterized by tropical and subtropical species that were transported northward due to coastal advection of warm waters associated with the El Niño of 2015-2016. North of PE, the warm-water affinity oceanic speciesAtlanta roseaandA. fragiliswere found, evidencing the entrance of water from the Central Pacific related to MHW which affected the oceanic region off the coast of PE. The response of the distribution patterns proves that atlantids can be used as biological indicators, as they reflect the effect of environmental anomalies in the southern CCS.

Pteropods and heteropods (Mollusca, Gastropoda, Thecosomata) and the Miocene Oxygen Minimum Zone, Trinidad

Fossil holoplanktonic mollusks (pteropods and heteropods) are so far little known from Trinidad and have not yet been employed in paleoenvironmental studies in this region. Specimens >125 µm were examined in samples from two sections of the Middle Miocene Brasso Formation of Central Trinidad. Samples from the type section at Brasso Village were younger (planktonic foraminiferal Zones N11–N12) than those from Nollis Tunnel, near Tabaquite (N8). Both sections yielded abundant holoplanktonic molluscs, but all were juveniles. At Brasso Village, yields were highest in samples collected near a bathyal oxygen minimum zone (OMZ) that was revealed using benthic foraminifera. The percentage of the fauna as Vaginella sp. did not vary significantly throughout this section, while Heliconoides sp. was concentrated in rocks deposited near the OMZ base and Creseis spina above the OMZ core. This implies depth stratification among the pteropods that limited the flux of Heliconoides sp. to shallower water samples. The fauna from Nollis Tunnel, where recovery was restricted to eight out of nine samples, was used to infer the position of the OMZ at this site. The assemblage was more abundant at Nollis Tunnel than at Brasso Village. Simultaneous confidence intervals show that the proportional abundance of Vaginella sp. did not vary significantly throughout the Nollis Tunnel section, while Creseis roesti and Heliconoides inflatus inflatus? showed depth stratification. This demonstrates that fossil holoplanktonic gastropods have potential as a tool for paleoenvironmental interpretations, especially in detecting fossil OMZs.

Assessing species boundaries in the open sea: an integrative taxonomic approach to the pteropod genus Diacavolinia

AbstractTo track changes in pelagic biodiversity in response to climate change, it is essential to accurately define species boundaries. Shelled pteropods are a group of holoplanktonic gastropods that have been proposed as bio-indicators because of their vulnerability to ocean acidification. A particularly suitable, yet challenging group for integrative taxonomy is the pteropod genus Diacavolinia, which has a circumglobal distribution and is the most species-rich pteropod genus, with 24 described species. We assessed species boundaries in this genus, with inferences based on geometric morphometric analyses of shell-shape variation, genetic (cytochrome c oxidase subunit I, 28S rDNA sequences) and geographic data. We found support for a total of 13 species worldwide, with observations of 706 museum and 263 freshly collected specimens across a global collection of material, including holo‐ and paratype specimens for 14 species. In the Atlantic Ocean, two species are well supported, in contrast to the eight currently described, and in the Indo‐Pacific we found a maximum of 11 species, partially merging 13 of the described species. Distributions of these revised species are congruent with well-known biogeographic provinces. Combining varied datasets in an integrative framework may be suitable for many diverse taxa and is an important first step to predicting species-specific responses to global change.

Vertical distribution and diurnal migration of atlantid heteropods

Understanding the vertical distribution and migratory behaviour of shelled holoplanktonic gastropods is essential in determining the environmental conditions to which they are exposed. This is increasingly important in understanding the effects of ocean acidification and climate change. Here we investigated the vertical distribution of atlantid heteropods by collating data from publications and collections and using the oxygen isotope (?18O) composition of single aragonitic shells. Data from publications and collections show 2 patterns of migration behaviour: small species that reside in shallow water at all times, and larger species that make diurnal migrations from the surface at night to deep waters during the daytime. The ?18O data show that all species analysed (n = 16) calcify their shells close to the deep chlorophyll maximum. This was within the upper 110 m of the ocean for 15 species, and down to 146 m for a single species. These findings confirm that many atlantid species are exposed to large environmental variations over a diurnal cycle and may already be well adapted to face ocean changes. However, all species analysed rely on aragonite supersaturated waters in the upper <150 m of the ocean to produce their shells, a region that is projected to undergo the earliest and greatest changes in response to increased anthropogenic CO2.

The old and the new plankton: ecological replacement of associations of mollusc plankton and giant filter feeders after the Cretaceous?

Owing to their great diversity and abundance, ammonites and belemnites represented key elements in Mesozoic food webs. Because of their extreme ontogenetic size increase by up to three orders of magnitude, their position in the food webs likely changed during ontogeny. Here, we reconstruct the number of eggs laid by large adult females of these cephalopods and discuss developmental shifts in their ecologic roles. Based on similarities in conch morphology, size, habitat and abundance, we suggest that similar niches occupied in the Cretaceous by juvenile ammonites and belemnites were vacated during the extinction and later partially filled by holoplanktonic gastropods. As primary consumers, these extinct cephalopod groups were important constituents of the plankton and a principal food source for planktivorous organisms. As victims or, respectively, profiteers of this case of ecological replacement, filter feeding chondrichthyans and cetaceans likely filled the niches formerly occupied by large pachycormid fishes during the Jurassic and Cretaceous.

Time-calibrated molecular phylogeny of pteropods.

Pteropods are a widespread group of holoplanktonic gastropod molluscs and are uniquely suitable for study of long-term evolutionary processes in the open ocean because they are the only living metazoan plankton with a good fossil record. Pteropods have been proposed as bioindicators to monitor the impacts of ocean acidification and in consequence have attracted considerable research interest, however, a robust evolutionary framework for the group is still lacking. Here we reconstruct their phylogenetic relationships and examine the evolutionary history of pteropods based on combined analyses of Cytochrome Oxidase I, 28S, and 18S ribosomal rRNA sequences and a molecular clock calibrated using fossils and the estimated timing of the formation of the Isthmus of Panama. Euthecosomes with uncoiled shells were monophyletic with Creseis as the earliest diverging lineage, estimated at 41–38 million years ago (mya). The coiled euthecosomes (Limacina, Heliconoides, Thielea) were not monophyletic contrary to the accepted morphology-based taxonomy; however, due to their high rate heterogeneity no firm conclusions can be drawn. We found strong support for monophyly of most euthecosome genera, but Clio appeared as a polyphyletic group, and Diacavolinia grouped within Cavolinia, making the latter genus paraphyletic. The highest evolutionary rates were observed in Heliconoides inflatus and Limacina bulimoides for both 28S and 18S partitions. Using a fossil-calibrated phylogeny that sets the first occurrence of coiled euthecosomes at 79–66 mya, we estimate that uncoiled euthecosomes evolved 51–42 mya and that most extant uncoiled genera originated 40–15 mya. These findings are congruent with a molecular clock analysis using the Isthmus of Panama formation as an independent calibration. Although not all phylogenetic relationships could be resolved based on three molecular markers, this study provides a useful resource to study pteropod diversity and provides general insight into the processes that generate and maintain their diversity in the open ocean.

First Record of Janthina globosa Swainson, 1822 (Mollusca, Gastropoda) and Prostheceraeus giesbrechtii Lang, 1884 (Platyhelminthes) in the Gulf of Antalya

During the survey study, a holo-planktonic gastropod species Janthina globosa Swainson, 1822 was captured for the first time during trawl shootings at 20-30 m depths from the Gulf of Antalya on 24th June 2015. On 15th July 2015, during the underwater diving, a colourful flatworm Prostheceraeus giesbrechtii was observed at the hard substratum depths of 5-7 m near the old Harbour (Antalya) (36o 35’ 5,15’’N; 30o 42’ 1,45’’E). The flatworm was taken to laboratory and photographed. Its length was approximately 2-3 cm and 1-1.5 mm thick. This species is the first record for the Gulf of Antalya, the North-eastern Mediterranean part of Turkey.