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Theme: Combined session: Ocean acidification andEvolution, systematics and developmental biologyPhylogeny of the Tanaidacea of the suborder Apseudomorpha (Crustacea:Malacostraca)Anna Stępień, Piotr Jóźwiak, Magdalena Błażewicz-PaszkowyczUniversity of Lodz, PolandEmail: stepie.anna@gmail.comTanaidacea are small marine crustaceans present in various marine habitats.Currently they are represented by almost 1200 nominal species, but it is assumedthat the total number of tanaidaceans might be a order of magnitude higher. In modernsystematics tanaidaceans are divided into three extant suborders: Apseudomorpha,Neotanaidomopha and Tanaidomorpha; the fourth suborder, Anthracocaridomorpharepresents exclusively extinct taxa.This study presents the first analysis of the phylogenetic relationships of theApseudomorpha, which is presumed to be the most plesiomorphic suborder of currentTanaidacea. The data matrix prepared with MESQUITE ver. 2.74 included 90 generaand 94 (72 binary and 22 multistate) unordered characters. Opsipedon, an extinctand apparently phylogenetically primitive genus been chosen as a representative ofan outside group.Phylogenetic analysis was conducted with T.N.T. (ver. 1.1). Bremer support wascalculated to assess branch support. A consensus tree was calculated from the tenmost parsimonious trees of the length of 744 steps; consistency index and retentionindex were 0.17 and 0.58 respectively.The cladogram derived resulted in only two clades which were consistent with thecurrent taxonomy; in consequence the status of eleven currently defined familiesis questioned. It can be concluded that the Kalliapseudidae and Sphyrapodidaewere the only monophyletic families, with Bremer support = 2 and 3 respectively.The Parapseudidae and Apseudidae are apparently polyphyletic although somemembers of the Leviapseudinae (fam. Apseudidae) form a separate clade (Br =2).The Chondropodinae, currently a subfamily of the Metapseudidae, together with thegenera as Francapseudes and Ascumnella (members of the Sphyrapodidae andParapseudidae, respectively) may represent a new higher taxon. The remainingMetapseudidae were grouped into a large and well-supported clade (Br =2 ) togetherwith members of the Pagurapseudidae, Whiteleggiidae, Sphaeromapseudidae,Tanzanapseudidae and Pagurapseudopsididae. This last result confirms a commonconcept (Sieg 1980, 1983; Gutu (1996) that these families constitute a group ofclosely-related taxa which could be defined as a superfamily.- 50 -