Recognition of Parapinnixidae Števčić, 2005, and Tetriasidae fam. nov. in Pinnotheroidea De Haan, 1833 (Crustacea: Brachyura: Thoracotremata).

The systematic position of three aberrant pinnotheroid genera: Tetrias Rathbun, 1898, Parapinnixa Holmes, 1895 and Sakaina Serène, 1964, are reappraised. A new family, Tetriasidae fam. nov. is established for Tetrias, and Parapinnixidae Števčić, 2005, is recognised for Parapinnixa and Sakaina. Tetriasids differ from all other pinnotheroids in that the articles of the palp of the third maxilliped (carpus, propodus and dactylus) are large and the dactylus is inserted at the distolateral corner of the propodus, whereas parapinnixids are distinctive in having the buccal cavern relatively small, subtriangular with the third maxilliped ischiomerus small, mesioproximally produced to form a triangular projection and is completely fused. The two families are phylogenetically distinct from the family Pinnotheridae based on the multi-locus gene tree, and are basal or near basal lineages in the Pinnotheroidea.