A Systematic and Taxonomic Review of the Family Pseudotanaidae (Crustacea: Peracarida: Tanaidacea) Based Primarily on Morphometric Cladistic Analysis
Species of the tanaid family Pseudotanaidae, established by Jurgen Sieg in 1973, have been reported from all the world's oceans in depths ranging from near the surface to below 6,000 m. The family currently consists of 46 characteristically small tanaidomorph species residing in two subfamilies, the Cryptocopinae (seven species) and the Pseudotanainae (39 species). Members of the more ancestral Crytocopinae differ from the Pseudotanainae by having females with four rather than three antennule articles and a complete separation of the maxilliped endites. The primary objective of this study was to test the hypothesis that the current structure of the family Pseudotanaidae should remain intact as a monophyletic group or, alternatively, should be pared to exclude the members of the current subfamily Cryptocopinae. A heuristic search using the parsimony optimality criterion was conducted on 69 unordered and unweighted morphological characters to test the relationships among 53 species of Pseudotanaidae and four out-groups. Six equally parsimonious trees were obtained that showed substantial support values at the node dividing Pseudotanainae from Cryptocopinae, thus providing strong evidence for removing Crytocopinae from the family Pseudotanaidae. A new family, Cryptocopidae is proposed containing the subfamilies Cryptocopinae (one species), Cryptocopoidinae (three species), and Iungentitanainae (four species). The remaining 46 species of Pseudotanaidae demonstrated inconsistent structure in the cladistic analysis due to the large amount of homoplasy among the characters used, thus suggesting a revised taxonomy based more on observed groupings of character traits rather than support values. Three subfamilies are recognized: the Akanthinotanainae (ten species), the Parapseudotanainae (two species) and the Pseudotanainae (33 species). The more ancestral Akanthinotanainae is represented solely by the new genus Akanthinotanais , a former subgenus of Pseudotanais . Two new sub-genera within the Akanthinotanainae are recognized: Akanthinotanais, s.s. with nine species and Guilleitanais represented by a single species, A. guillei , with unique ancestral characters. Among the Pseudotanainae, a single genus, Pseudotanais , and two sub-genera, Pseudotanais, s.s. and the new Mystriocentrus , are recognized. Seven new taxa including four species of Pseudotanais, s.s., one of Pseudotanais (Mystriocentrus) and one each of the genera Parapseudotanais and Cryptocopoides were discovered during this research.