Smirnouidaphnia, Kotov, 2007

Kotov, Alexey A., 2007, Jurassic Cladocera (Crustacea, Branchiopoda) with a description of an extinct Mesozoic order, Journal of Natural History 41 (1 - 4), pp. 13-37 : 23-24

Tribe SIDINI Baird, 1850

Smirnouidaphnia gen. nov.

Type species. Smirnoυidaphnia smirnoυi sp. nov.

Etymology

This genus is dedicated to the outstanding investigator of Recent and fossil cladocerans, Professor Nikolai Nikolaevich Smirnov. Most probably, the first representative of this genus was described under the name Archedaphnia testacea Smirnov, 1971 from Novospasskoye as a member of the family Daphniidae Straus, 1820 . The second part of the new genus name refers to the genus Daphnia O. F. Müller, 1785 , the type genus of the family Daphniidae , into which Smirnoυidaphnia testacea was initially placed. But it is S. smirnoυi sp. nov. from Ust’-Baley which is selected here as the type species of the genus due to a significantly better preservation of specimens.

Diagnosis

Antennal exopod three-segmented, its second and third segments with numerous setae. All setae of endopod uniform, unspecialized. Spines on all segments except apical endopod segment, absent (or very small and due to this were not preserved in fossils). Endites on inner-distal portions of limbs not fused.

Differential diagnosis

The most spectacular difference of Smirnoυidaphnia from all Recent ctenopods is the presence of projecting unfused endites on inner-distal portions of thoracic limbs. Among eight valid Recent and fossil genera of the Sidinae described previously ( Korovchinsky 2004; Kotov and Korovchinsky 2006), only two genera ( Sida and Limnosida ) have a three-segmented exopod of AII. They were placed by Korovchinsky (1986) in the tribe Sidini Baird, 1850 , but this grouping must be checked (because it was based on symplesiomorphies). In any case, Smirnoυidaphnia gen. nov. has numerous (up to 12) lateral setae on the second segment of the exopod of AII, which distinguishes it from the Recent genera Sida and Limnosida with three to four setae there. Probably, the third segment of AII in Smirnoυidaphnia also has more setae than Sida or Limnosida , but their number cannot be counted in S. testacea .

Age

Lower-Middle Jurassic.