Department of Polar Biology and Oceanobiology, University of Łódź, Łódź, Poland.
PLoS One. 2012;7(4):e33068. doi: 10.1371/journal.pone.0033068. Epub 2012 Apr 4.
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.
糠虾类是小型等足甲壳动物，存在于所有海洋生境中，深度范围广泛，很少进入淡水。然而，它们的生命周期中没有强制性的扩散阶段。因此，种群不可避免地会被隔离，并且会出现异域物种形成和高区域多样性；世界性分布被认为是不可能或不存在的。讨论了被动扩散的选择。糠虾类似乎首先在浅水区进化，这是 Apseudomorpha 和一些糠虾类科的最大多样化区域，而在更深的水域，Apseudomorpha 随后进化出了两到三条不同的谱系。Neotanaidomorpha 已经在深海中独立进化并多样化，而 Tanaidomorpha 经历了最大的进化、多样化和适应，以至于一些深海分类群正在重新殖民浅水区。对其地理分布的分析表明存在一定程度的区域隔离，但存在多系群分类群的纳入和普遍缺乏数据的问题，特别是对于深海。结论是，深海和某些海洋区域的糠虾类多样性有待发现；较小的分类群在很大程度上未得到研究；还有许多隐种有待区分。因此，目前公认的物种数量可能低了一个数量级，在全球范围内，糠虾类在多样性上可能与十足目和等足目相媲美。
