Diversity of Tanaidacea (Crustacea: Peracarida) in the World\u27s Oceans - How Far Have We Come?

Tanaidaceans are small peracarid crustaceans which occur in all marine habitats, over the full range of depths, and rarely into fresh waters. Yet they have no obligate dispersive phase in their life-cycle. Populations are thus inevitably isolated, and allopatric speciation and high regional diversity are inevitable; cosmopolitan distributions are considered to be unlikely or non-existent. Options for passive dispersion are discussed. Tanaidaceans appear to have first evolved in shallow waters, the region of greatest diversification of the Apseudomorpha and some tanaidomorph families, while in deeper waters the apseudomorphs have subsequently evolved two or three distinct phyletic lines. The Neotanaidomorpha has evolved separately and diversified globally in deep waters, and the Tanaidomorpha has undergone the greatest evolution, diversification and adaptation, to the point where some of the deep-water taxa are recolonizing shallow waters. Analysis of their geographic distribution shows some level of regional isolation, but suffers from inclusion of polyphyletic taxa and a general lack of data, particularly for deep waters. It is concluded that the diversity of the tanaidomorphs in deeper waters and in certain ocean regions remains to be discovered; that the smaller taxa are largely understudied; and that numerous cryptic species remain to be distinguished. Thus the number of species currently recognized is likely to be an order of magnitude too low, and globally the Tanaidacea potentially rival the Amphipoda and Isopoda in diversity

Diversity of Tanaidacea (Crustacea: Peracarida) in the World's Oceans – How Far Have We Come?

Tanaidaceans are small peracarid crustaceans which occur in all marine habitats, over the full range of depths, and rarely into fresh waters. Yet they have no obligate dispersive phase in their life-cycle. Populations are thus inevitably isolated, and allopatric speciation and high regional diversity are inevitable; cosmopolitan distributions are considered to be unlikely or non-existent. Options for passive dispersion are discussed. Tanaidaceans appear to have first evolved in shallow waters, the region of greatest diversification of the Apseudomorpha and some tanaidomorph families, while in deeper waters the apseudomorphs have subsequently evolved two or three distinct phyletic lines. The Neotanaidomorpha has evolved separately and diversified globally in deep waters, and the Tanaidomorpha has undergone the greatest evolution, diversification and adaptation, to the point where some of the deep-water taxa are recolonizing shallow waters. Analysis of their geographic distribution shows some level of regional isolation, but suffers from inclusion of polyphyletic taxa and a general lack of data, particularly for deep waters. It is concluded that the diversity of the tanaidomorphs in deeper waters and in certain ocean regions remains to be discovered; that the smaller taxa are largely understudied; and that numerous cryptic species remain to be distinguished. Thus the number of species currently recognized is likely to be an order of magnitude too low, and globally the Tanaidacea potentially rival the Amphipoda and Isopoda in diversity

The Magnitude of Global Marine Species Diversity

Background: The question of how many marine species exist is important because it provides a metric for how much we do and do not know about life in the oceans. We have compiled the first register of the marine species of the world and used this baseline to estimate how many more species, partitioned among all major eukaryotic groups, may be discovered. Results: There are ∼226,000 eukaryotic marine species described. More species were described in the past decade (∼20,000) than in any previous one. The number of authors describing new species has been increasing at a faster rate than the number of new species described in the past six decades. We report that there are ∼170,000 synonyms, that 58,000–72,000 species are collected but not yet described, and that 482,000–741,000 more species have yet to be sampled. Molecular methods may add tens of thousands of cryptic species. Thus, there may be 0.7–1.0 million marine species. Past rates of description of new species indicate there may be 0.5 ± 0.2 million marine species. On average 37% (median 31%) of species in over 100 recent field studies around the world might be new to science. Conclusions: Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century

Apseudomorphan adaptations. a, <i>Kalliapseudes</i> sp. with a filter-feeding apparatus on the chelipeds; b, <i>Cyclopoapseudes</i> sp., with a flattened body adapted to burying in the upper layer of soft sediments; c, <i>Macrolabrum</i> sp., with its twisted posterior thorax and abdomen, adapted to living inside empty snail shells, d; <i>Tanzanapseudes</i> sp., with a flattened body adapted to life on and between flat surfaces of coral rubble; e, <i>Bunakenia</i> sp with its pereopods adapted to digging in soft sediments.

<p>Apseudomorphan adaptations. a, <i>Kalliapseudes</i> sp. with a filter-feeding apparatus on the chelipeds; b, <i>Cyclopoapseudes</i> sp., with a flattened body adapted to burying in the upper layer of soft sediments; c, <i>Macrolabrum</i> sp., with its twisted posterior thorax and abdomen, adapted to living inside empty snail shells, d; <i>Tanzanapseudes</i> sp., with a flattened body adapted to life on and between flat surfaces of coral rubble; e, <i>Bunakenia</i> sp with its pereopods adapted to digging in soft sediments.</p

New tanaidomorph Tanaidacea (Crustacea: Peracarida) from submarine mud-volcanoes in the Gulf of Cadiz (North-east Atlantic)

Faunal collections from mud-volcano sites in the Gulf of Cadiz, at depths between 355 and 3061 m, have revealed a high diversity (and in some cases high density) of tanaidaceans. The present study reports on nine new tanaidomorph species from eight different genera from this material. These include representatives of genera known elsewhere from non-vent-associated deep-sea habitats, but notably only the second and third (respectively) representatives of two genera, Coalecerotanais and Cristatotanais, known previously from cold-seep-habitats in the Gulf of Mexico. The genus Spinitanaopsis is synonymized with Cristatotanais. The tanaidacean records to date from hydrothermal vents or cold seeps are collated as a context for the present material. The possibilities of habitat-endemism in tanaidacean taxa associated with reducing environments and their biogeography are discussed.Training Through Research Programme IOC-UNESCOEC FP6 - GOCE-CT-2005-511234 HERMESMNiSW grant 2PO4C 089 29Census of Marine Life - COMARG

Cumulative curve of the number of species known (published) from Australian waters since the first published in 1882 (histogram bars illustrate the number published each year).

<p>Cumulative curve of the number of species known (published) from Australian waters since the first published in 1882 (histogram bars illustrate the number published each year).</p

Tanaidacea of the Amundsen and Scotia Seas: an unexplored diversity

The Scotia Arc and Amundsen Sea are contrasting regions within West Antarctica. The Scotia Sea shelf is well studied and central to the origin and diversity of the Southern Ocean benthic fauna, whilst the shelf of Amundsen Sea is one of the least studied shelf areas in the world; a ‘white spot’ on the map of benthic research. Here we report on the tanaidaceans collected using an epibenthic sledge on two expeditions, BIOPEARL 1 and 2, of the RRS James Clark Ross in 2006 and 2008, respectively. This study represents the first analysis of the tanaidacean fauna of those two basins. Thirty-seven species were found in the Amundsen Sea from 500–1500 m depth and 51 species were found at depths ranging from 200–1600 m in the Scotia Sea. In the Scotia Sea, many species were unique to each of the study sites which may be evidence of allopatric speciation episodes. Site specificity was especially evident for Typhlotanais and Pseudotanais. Only three species were common to both basins. Around 90% of the species were previously undescribed. Our findings increase the number of the tanaidaceans known in the Southern Ocean by 50%

Cluster analysis of Bray-Curtis similarities (%) between various sea-areas, based on the numbers of species of tanaidacean genera (or higher taxa, see text) per region, for: a, shallow waters, <200 m depth, and: b, deep waters. A, B and C are clusters referred to in the text.

<p>Cluster analysis of Bray-Curtis similarities (%) between various sea-areas, based on the numbers of species of tanaidacean genera (or higher taxa, see text) per region, for: a, shallow waters, <200 m depth, and: b, deep waters. A, B and C are clusters referred to in the text.</p

Cumulative number of tanaidacean species described in each decade since 1800.

<p>Cumulative number of tanaidacean species described in each decade since 1800.</p