Genus Tanais Latreille, 1831

Diagnosis. Four pleonites present plus pleotelson. Pleonites 1 and 2 carrying a transverse dorsal row of plumose setae. Antennule with four articles, first article at least 2.5 times length of second article, terminal article with four to seven aesthetascs. Antenna with seven articles, article 2 longer than wide, last two articles small. Maxillule endite with eight large terminal spiniform setae, palp with several long setae. Labium outer lobe with rounded terminal process. Pereopod 1 coxa without anterior bulge. Pleopod basis with one or two plumose setae on inner margin and seven to twelve on outer margin, endopod inner margin with seven to twelve plumose setae. Uropod with three or four articles, terminal article normal. Sexually dimorphic.