Cryptic mitochondrial lineages in the widespread pycnogonid Colossendeis megalonyx Hoek, 1881 from Antarctic and Subantarctic waters

Colossendeis megalonyx Hoek, 1881 is a widespread and abundant pycnogonid in the Southern Ocean which has also been reported from the South Atlantic and South Pacific Oceans. Its strictly benthic lifestyle is expected to promote genetic differentiation among populations and ultimately facilitate speciation. On the other hand, the reported eurybathy and unknown larval stages of this species may allow Colossendeis megalonyx to maintain genetic continuity between isolated shallow-water habitats by active dispersal through the deep sea or by passive rafting on floating substrates. Thus, it remains unknown whether and to which extent geographically separated populations of Colossendeis megalonyx maintain gene flow in the Southern Ocean. We sampled 96 specimens of Colossendeis megalonyx from three stations in the Atlantic Sector of the Southern Ocean and one station from the South American continental shelf (Burdwood Bank). The genetic structure of nominal Colossendeis megalonyx as well as its phylogenetic position within the genus Colossendeis were assessed using a fragment of the cytochrome c oxidase subunit 1 gene. Our data strongly support that nominal Colossendeis megalonyx consists of at least five cryptic and one pseudocryptic mitochondrial lineages, four of which appear to be geographically restricted. Two lineages occurred at locations separated by more than 1,000 km in the Antarctic, thus indicating high levels of gene flow or recent colonization. No haplotype sharing across the Polar Frontal Zone was observed. Our results strongly suggest that cryptic speciation occurred within the genus Colossendeis. The wide biogeographic distribution range of Colossendeis megalonyx and perhaps that of other Antarctic pycnogonids should therefore be regarded with caution.     

Sponges Collected by the Swedish Deep Sea Expedition

The paper deals with sponges collected in the Atlantic by the Swedish Deep Sea Expedition. The collection contains six species of the genera Malaco-saccus, Chonelasma, heptonema, Asbestopluma , and Chondrocladia , which are well known from the deep-sea. Three new species are described, viz. Asbestopluma quadriserialis sp.n., Chondrocladia al-batrossi sp.n., and C. burtoni sp.n. A survey of the knowledge of the Atlantic deep-sea sponge fauna shows that 118 species are at present known from depths of more than 2 000 m. About 35% of the species were found four or more times, whereas about 47% are known only from the type locality. 63 species were taken more than once, and 50 species are known also from depths of less than 2 000 m.     

Pycnogonids of the Eastern Weddell Sea (Antarctica), with remarks on their bathymetric distribution

The current work presents new data on the pycnogonids collected during the ANTXXI/2 cruise on board of “Polarstern” R/V during December 2003 and January 2004 in the Eastern Weddell Sea (Antarctica). Twenty-eight samples were taken, with different trawls, from depths between 120 and 1,866 m. In total, 251 specimens of pycnogonids, belonging to 31 species, were collected. Five species were observed to increase their depth range while six were found for the first time in the Weddell Sea, exhibiting an expansion in their geographical distribution, and confirming the general trend toward the circumpolarity of this group (23 of 31 species were circumpolar). Pallenopsis kupei is new for Antarctic waters. The most abundant species were Colossendeis megalonyx and Nymphon australe. Current data were completed with the samples collected from the same region during Polarstern cruise ANTXIII/3 (EASIZ I) in February–March 1996. Bathymetric patterns of distribution were analyzed for the total of 1,564 specimens (82 species, 14 genera). The results showed a difference in the composition between the continental shelf (from 100 to 900 m depth) and the slope (below 900 m), where the genus Nymphon dominated. Depth seems to be an influential factor in the structure of pycnogonid assemblages.     

Some deep water Pycnogonids from the north-east Atlantic

Twenty-two specimens of pycnogonid representing nine species arc recorded from deep waters around the British Isles. The samples are from the Faroe Channel, the Hebridean Terrace and the vicinity of the Great Sole Bank, taken at depths of between 200 and 1835 m. These specimens demonstrate marked southern range extensions for Aymphon teptocheles and Pallenopsis tritonis , and include the northernmost record for the genus Cilunculus ( C. alcicornis ) and the third European record for Colossendeis arcuata . Protonymphon larvae of N. leptocheles and Paranymphon spinosum are figured.     

Reproduction in marine invertebrates in “stable” environments: the deep sea model

Summary

Studies over the last 15 years have revealed that deep-sea benthic megainvertebrates show a variety of reproductive patterns that are adapted to the deep-sea, an environment in which the fauna occurs at low densities and resources are sparse. In the NE Atlantic the majority of species reproduce year round whilst a limited number of species reproduce on a seasonal basis believed to be entrained by the deposition of surface derived organic material on the deep-sea bed. A third pattern of rapid growth and early reproduction is found in a limited number of species that utilize unpredictable and ephemeral resources in the deep sea. Examination of the fertilization and behavioural biology of species from the bathyal depths suggest some species enhance fertilization success by forming pairs during their breeding season. However, the same concentration of sperm, as seen in shallow water invertebrates, is required for successful fertilization. At least one deep-sea species of echinoid requires high pressure for successful embryogenesis suggesting a depth-related segregation of deep-sea fauna. The origin of megafaunal populations of deep-sea invertebrates in the N. Atlantic is discussed in the light of these new data in relation to varying reproductive patterns and the environmental changes that have occurred during the last deglaciation.     

PYCNOIB: Biodiversity and Biogeography of Iberian Pycnogonids

Biodiversity and biogeographic studies comparing the distribution patterns of benthic marine organisms across the Iberian Atlantic and Mediterranean waters are scarce. The Pycnogonida (sea spiders) are a clear example of both endemicity and diversity, and are considered a key taxon to study and monitor biogeographic and biodiversity patterns. This is the first review that compiles data about abundance and diversity of Iberian pycnogonids and examines their biogeographic patterns and bathymetric constraints using GIS tools. A total of 17762 pycnogonid records from 343 localities were analyzed and were found to contain 65 species, 21 genera and 12 families. Achelia echinata and Ammothella longipes (family Acheliidae) were the most abundant comprising ~80% of the total records. The Acheliidae is also the most speciose in Iberian waters with 15 species. In contrast, the family Nymphonidae has 7 species but is significantly less abundant (<1% of the total records) than Acheliidae. Species accumulation curves indicate that further sampling would increase the number of Iberian species records. Current sampling effort suggests that the pycnogonid fauna of the Mediterranean region may be richer than that of the Atlantic. The Strait of Gibraltar and the Alboran Sea are recognized as species-rich areas that act as buffer zones between the Atlantic and Mediterranean boundaries. The deep waters surrounding the Iberian Peninsula are poorly surveyed, with only 15% of the sampling sites located below 1000 m. Further deep-water sampling is needed mainly on the Iberian Mediterranean side.     

Locomotory mechanisms in Antarctic pycnogonids

Patterns of walking, modes of joint movement, and individual limb diversity were analysed with the aid of ciné film of several living Antarctic pycnogonids, including the 8-legged Colossendeis australis, C. angusta, Pallenopsis patagonica , and Nymphon sp., the 10-legged Decolopoda australis , and the 12-legged Dodecolopoda mawsoni. Appendage musculature of several of these species and also of the 10-legged Pentapycnon charcoti and Pentanymphon antarcticurn was dissected. At least two distinct morphotypes were identified: a short-legged, crawling variety ( P. charcoti ); and the more typical long-legged, large bodied, walking forms. No gross differences in musculature of joints were noted in the species examined. All joints are, at least superficially, hinge joints. The coxa-body joint is largely immobile, the coxa 1-coxa 2 joint alone exhibits promotion-remotion and all other joints are flexion-extension joints. The 8-legged forms move in an imprecise manner, there being irregularity of leg raising and lowering and where legs touch down in relation to the body and to other legs. The 10- and 12-legged forms exhibit more precise patterns of metachronal leg movements. Although legs move in a basic promotion-remotion, extension-flexion mode, there is a certain degree of twisting of a leg as it is picked up, brought forward, and set down; models indicating how such joint movement occurs were constructed. The possibility that hydrostatic pressure is employed in extension is considered and is found to be remote. Lateral placement of legs, orientated in almost all directions in the horizontal plane of the trunk, achieves a versatility of movement similar to that in crabs. Comments on pycnogonid taxonomic affinities are offered.     

Diversity of isopods (Crustacea): new data from the Arctic and Atlantic Oceans

New data on the diversity pattern of isopods (Crustacea) from the northern most part of the North Atlantic and the Arctic Oceans is presented. The pattern of diversity with depth is similar at depths <1000m, but differs considerably below about 1000m. In the Arctic the diversity of isopods (expressed both as numbers of species per sled and expected number of species) increased with increased depth to a maximum at depths of about 320 to 1100m, but then declined towards deeper waters. There was a significant increase in numbers per sled and in the expected number of species with increased depth in the northernmost part of the North Atlantic Ocean. Additionally, changes occurred in the relative composition of the shallow and deep water fauna, with asellote isopods being relatively larger part of the isopod fauna in the Arctic than in the northern most part of the North Atlantic. This indicates major faunistic changes occurring at the Greenland-Iceland-Faeroe Ridge, possibly caused by rapid changes in the temperature. Furthermore, that the low diversity of the Arctic deep-sea is a regional phenomenon, and not a part of a large scale latitudinal pattern in the North Atlantic.     

From Europe to America: pliocene to recent trans-atlantic expansion of cold-water north atlantic molluscs

Data on the geographical distribution, phylogeny and fossil record of cool-temperate North Atlantic shell-bearing molluscs that live in waters shallower than 100 m depth belong to two biogeographic provinces, one in eastern North America north of Cape Cod, the other in northern Europe. Amphi-Atlantic species, which are found in both provinces, comprise 30.8% of the 402 species in the northeastern Atlantic and 47.3% of the 262 species in the northwestern Atlantic. Some 54.8% of these amphi-Atlantic species have phylogenetic origins in the North Pacific. Comparisons among fossil Atlantic faunas show that amphi-Atlantic distributions became established in the Middle Pliocene (about 3.5 million years ago), and that all represent westward expansions of European taxa to North America. No American taxa spread eastward to Europe without human assistance. These results are in accord with previous phylogeographic studies among populations within several amphi-Atlantic species. Explanations for the unidirectional expansion of species across the Atlantic remain uncertain, but may include smaller size and greater prior extinction of the North American as compared to the European fauna and biased transport mechanisms. Destruction of the European source fauna may jeopardize faunas on both sides of the Atlantic.     

Evidence from morphological and genetic data confirms that Colossendeis tenera Hilton, 1943 (Arthropoda: Pycnogonida), does not belong to the Colossendeis megalonyx Hoek, 1881 complex

Within the Pycnogonida, genetic studies have revealed that Colossendeis megalonyx Hoek (Challenger Report, Zoology, 3(X), 1–167, 1881), consists of a complex of several cryptic or overlooked species. Colossendeis megalonyx is a typical Southern Hemisphere species complex distributed primarily on the continental shelves in the Antarctic and Subantarctic. However, a different Colossendeis species with a completely different geographic distribution range, Colossendeis tenera Hilton (Journal of Entomology and Zoology, Pomona College, Claremont, 35(1), 2–4, 1943), was considered a subspecies of Colossendeis megalonyx by Turpaeva (Trudy Instituta Okeanology "P. P. Shirshova", Akademy Nauk SSSR, 103, 230–246, 1975). Colossendeis tenera occurs predominantly along the Pacific Coast of North America from the Bering Sea to central California. Prominent differences between these two currently distinct species are found in body proportions and other characters that were interpreted by Turpaeva as a possible case of pedomorphosis induced by deep-sea conditions. In this study, we tested the hypothesis that Colossendeis tenera belongs to the Colossendeis megalonyx complex by analyzing available and novel sequence data (CO1 and H3) of both Colossendeis megalonyx and Colossendeis tenera as well as a similar, apparently closely related species, Colossendeis angusta Sars (Archiv for Mathematik og Naturvidenskab, 2, 237–271, 1877). We compared morphometric data and SEM of the ovigera of these species. Our results clearly indicate that Colossendeis tenera and Colossendeis angusta are not a part of the Colossendeis megalonyx complex. A sister-group relationship of Colossendeis tenera and Colossendeis angusta is strongly supported, but Colossendeis tenera is not clearly resolved as monophyletic with respect to Colossendeis angusta. This work highlights the need for further examination of the variation found in the tenera-angusta clade. It also gives a first hint of the phylogenetic affinities of species within Colossendeis.     

Postembryonic development of Nymphon unguiculatum Hodgson 1915 (Pycnogonida, Nymphonidae) from the South Shetland Islands (Antarctica)

Male specimens of the sea spider species Nymphon unguiculatum, carrying eggs, larvae and postlarvae in various stages of development, were collected off the South Shetland Island at water depths between 112 and 472 m in austral summer 2006/2007. Here, we describe the external morphology of four postembryonic stages (protonymphon, instar 1, instar 2, and instar 3) carried by these specimens. We found that (1) protonymphon larvae hatch from the eggs; (2) larvae and postlarval stages have yolk reserves and are characterized by a relatively large size (average body lengths of 0.46, 0.55, 0.65 and 0.73 mm in the successive stages); (3) postlarvae remain on the ovigerous legs of males during several moults; (4) a spinning apparatus is present; (5) the development of walking legs is sequential. The larval and postlarval development of N. unguiculatum is compared with that known from other pycnogonid species.     

A scanning-electron microscopic study of <Emphasis Type="Italic">Dickdellia labioflecta</Emphasis> (Dell, 1990) (Gastropoda,Littorinoidea) on <Emphasis Type="Italic">Colossendeis megalonyx megalonyx</Emphasis> Fry and Hedgpeth, 1969 (Pycnogonida,Colossendeidae): a test for ectoparasitism

A scanning-electron microscopic (SEM) study of a clutch of eggs and juveniles of Dickdellia labioflecta on Colossendeis megalonyx megalonyx revealed that the young snails remove the upper layers of the pycnogonid cuticle, most probably by rasping. This way holes are created in the cuticle that could serve as a potential source of food for the snail. Measurements and statistics show that the holes have the same density as the cuticular glands. These glands are spread all over the pycnogonid cuticle. Additionally, they are filled with cytoplasmic material having a fine structure and cuticular surrounding that is typical for those glands. Hence, it is suggested that the snails get access to the interior of the pycnogonid through the holes and glands. Holes in the cuticle are absent under smaller Dickdellia specimens, but they are formed consecutively as they become older and grow larger. It is suggested that Dickdellia snails are ectoparasites because this would allow them to remain on pycnogonids until they exceed the initial egg volume, which would be difficult to explain without additional food uptake from the pycnogonid host.     

The Lepocreadiidae Odhner, 1905 (Digenea) of fishes from the north-east Atlantic: summary paper,with keys and checklists

Results published in seven previous papers on the Lepocreadiidae are summarised and keys are given to the 19 species of lepocreadiid parasite from north-eastern Atlantic fishes. Diagnoses for the family and the two subfamilies represented in the north-eastern Atlantic are presented. Parasite-host and host-parasite lists, arranged in taxonomic order, are given. The NE Atlantic fauna is dominated numerically by members of the subfamily Lepidapedinae, which occur most frequently in gadiform fishes, often in the deep-sea.The three lepocreadiine forms are parasites of cosmopolitan fishes or fish families that predominate in warm waters.     

A new deep-sea hydroid (Cnidaria: Hydrozoa) from the Bering Sea Basin reveals high genetic relevance to Arctic and adjacent shallow-water species

The marine benthic fauna in Arctic shallow-water is reported to be a relatively young assemblage by species of either Pacific or Atlantic affinity. Whether current deep-sea Pacific species are included in the affinity or not is unknown. Combining morphological comparisons and genetic analyses, a new deep-sea hydroid to science, Sertularia xuelongi sp. nov. (Cnidaria: Hydrozoa: Sertulariidae), is described from the northern margin of the Bering Sea Basin at depths of 800–1570 m collected in 2010. It is characterized by slender and zigzag-shaped hydrocauli, alternately arranged hydrothecae and the absence of distal-lateral horns in fully matured female gonothecae. Its distribution, currently known only from Bering Sea Basin, suggests that it could not be an Arctic species with Pacific affinity. However, phylogenetic analyses based on the mitochondrial 16S rRNA gene show that it is clustered into a distinctive clade with four closely related species recorded from shallow-water of Northwest France, Iceland, Chukchi Sea and/or Bering Sea. In addition, its sequence similarity is highly relevant to these four species: Sertularia argentea (98.6 %), S. cupressina (98.8 %), S. plumosa (98.8 %) and S. robusta (99.4 %). All these provide a new insight into the relevance of North Pacific deep-sea species to the benthic fauna in Arctic and adjacent shallow-water. The taxonomic restriction of the genus Sertularia and the re-validation of the genus Polyserias are discussed. Future researches on more deep-sea species from Pacific and/or Atlantic are required to understand the evolution and speciation pattern involved in polar relevance.     

Salinity and temperature tolerance by Nymphon gracile (Leach) and Achelia echinata (Hodge) (Pycnogonida)

The tolerance of two species of pycnogonid, Achelia echinata (Hodge) and Nymphon gracile (Leach) to a range of salinities, temperatures and relative humidities has been examined. In most instances N. gracile is more resistant than A. echinata and indeed is found higher in the littoral zone during the warmer months and thus likely to be subjected to greater environmental fluctuation.     

珠江口及邻近海域大型底栖动物多样性随盐度、水深的变化趋势

利用2006年7-8月(夏季)、2007年4-5月(春季)和2007年10-12月(秋季)珠江丰水期、平水期和枯水期3个航次在南中国海北部珠江口附近海域4条由河口、近岸到深水区调查断面的数据, 研究大型底栖动物多样性由河口-近岸-深水的变化趋势及与环境因子的关系。春季、夏季和秋季分别获得大型底栖动物273、256和148种, 各季节均以环节动物种类最多, 节肢动物次之。大型底栖动物种类数、丰度、生物量和Shannon-Wiener多样性指数均由河口向近岸海域升高, 再由近岸向外海深水区降低。Pielou均匀度深水区最高, 其次为近岸。河口和深水区大型底栖动物k-优势度曲线位于近岸浅水域曲线之上, 表明生物多样性由河口向近岸升高, 而由近岸向深水则降低。大型底栖动物与环境因子Pearson相关性分析表明, 春、秋季大型底栖动物种类数、丰度和生物量与水深呈显著的负相关, 秋季种类多样性指数和均匀度也与水深呈显著的负相关性, 而夏季仅生物量与水深呈显著的负相关; 春、秋季大型底栖动物种类数、生物量、丰度、多样性指数和种类均匀度与盐度的相关性不显著, 但是夏季大型底栖动物种类数、丰度、多样性指数和种类均匀度与盐度呈显著正相关。单位面积(0.2 m²)内, 珠江口及邻近海域大型底栖动物在近岸浅水区较深水区和河口生物多样性高, 且生物量丰富。     

Predatory behavior of giant Antarctic sea spiders (Colossendeis) in nearshore environments

Pycnogonids in the genus Colossendeis are found in the deep sea and Southern Ocean. Although the genus contains the largest and most conspicuous species of sea spiders, little is known about their ecology or behavior. We documented two species feeding on a variety of benthic and pelagic invertebrates during three diving field seasons at McMurdo Station, Antarctica. Individuals of one species, Colossendeis megalonyx, fed on a variety of pelagic organisms, particularly the pteropod Clione antarctica. We used video to document rapid capture of individuals of C. antarctica by captive specimens of C. megalonyx in the laboratory, and we suggest that, at least in the nearshore environment, pelagic invertebrates are an important food source for this and potentially other pycnogonid species.     

Taxonomic notes on halacarids (Acari) from the Skagerrak area

A total of 27 halacarid species were found in sediments taken at 5–25 m depth off the western coast of Sweden. The four speciesCopidognathus magnipalpus, Actacarus obductus, Coloboceras longiusculus, andLohmannella multisetosa are new to the fauna of the northeastern North Atlantic; taxonomic diagnoses of these species are given.Anomalohalacarus septentrionalis andCamactognathus borealis, both new species, are described. Member of the Taxonomy Group at the Biologische Anstalt Helgoland     

Genetic structure of the deep-sea coral Lophelia pertusa in the northeast Atlantic revealed by microsatellites and internal transcribed spacer sequences

The azooxanthellate scleractinian coral Lophelia pertusa has a near-cosmopolitan distribution, with a main depth distribution between 200 and 1000 m. In the northeast Atlantic it is the main framework-building species, forming deep-sea reefs in the bathyal zone on the continental margin, offshore banks and in Scandinavian fjords. Recent studies have shown that deep-sea reefs are associated with a highly diverse fauna. Such deep-sea communities are subject to increasing impact from deep-water fisheries, against a background of poor knowledge concerning these ecosystems, including the biology and population structure of L. pertusa. To resolve the population structure and to assess the dispersal potential of this deep-sea coral, specific microsatellites markers and ribosomal internal transcribed spacer (ITS) sequences ITS1 and ITS2 were used to investigate 10 different sampling sites, distributed along the European margin and in Scandinavian fjords. Both microsatellite and gene sequence data showed that L. pertusa should not be considered as one panmictic population in the northeast Atlantic but instead forms distinct, offshore and fjord populations. Results also suggest that, if some gene flow is occurring along the continental slope, the recruitment of sexually produced larvae is likely to be strongly local. The microsatellites showed significant levels of inbreeding and revealed that the level of genetic diversity and the contribution of asexual reproduction to the maintenance of the subpopulations were highly variable from site to site. These results are of major importance in the generation of a sustainable management strategy for these diversity-rich deep-sea ecosystems.     

The energy cost of off-shore migration in Nymphon gracile (Pycnogonida)

The transportation off-shore of the littoral pycnogonid Nymphon gracile during the winter months is facilitated by the ebb tide swimming of this otherwise benthic animal. The energy cost of migration has been estimated from measurements of oxygen consumption and drag forces acting on the different segments of the leg during swimming. The swimming patterns of N. gracile both under constant conditions and in response to tidal pressure cycles are considered in relation to the animals' energy reserves.