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

Aspects of biogeography, systematics and ecolomorphology of deep-sea Tanaidacea (Crustacea, Peracarida)

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A comparative study on the tubes and feeding behaviour of eight species of corophioid Amphipoda and their bearing on phylogenetic relationships within the Corophioidea

Observations are presented on mouthpart functional morphology, and on feeding, grooming and defaecatory behaviour of eight species of corophioid Amphipoda, viz. Corophium bonnellii, Lembos websteri, Aora gracilis, A. spinicornis, Gammaropsis nitida, Ericthonius punctatus, Jassa falcata and J. marmorata. These data are considered in relation to tube structure and amphipod posture in relation to the tube. All these species occupy double-ended cylindreical tubes made from 'amphipod silk' secreted by the third and fourth preraeopods, incorporating sediment and other debris to varying degrees. Uniquely among this set of species, however, E. punctatus has a tube that is architecturally distinct. It tapers along its length and has a distinctive oblique main entrance at its widest end. This end is used preferentially. The other species studied use either opening with equal facility. Such a feature is adaptive in facilitating deployment of the antennae and shielding the head of E. punctatus. Two groupings of species are propose: group A which feed inside their tube using pleopod-induced through-tube currents, and group B which feed outside or at the entrance to their tube using external water currents. Group A includes C. bonnellii, L. websteri and the Aora species. Group B includes E. punctatus and the Jassa species. Gammaropsis nitida exhibits traits from both groups, adding weight to its perceived status as a genus representative of the stem corophioid. The ischyrocerid habit of externalizing food-gathering may be regarded as the first step along an evolutionary line leading to the rod-building podocerid types and ultimately towards the caprellids. All species examined show a degree of flexibility in their feeding habits which helps to explain the success of this taxon, which has radiated into a great diversity of aquatic biotopes