Description of Ilyocryptus nevadensis (Branchiopoda, Anomopoda), a new species from a high altitude crater lake in the volcano Nevado de Toluca, Mexico

A new species of a cladoceran fi om a crater-lake, located at 4120 m a.s.l. in the volcano Nevado de Toluca, Mexico, is here described. It belongs to the genus llyocryptus, and is distinguished mainly by a combination of feat ures, including an incomplete moulting; the anal opening is located on the distal end of the postabdomen, which is armed with moveable lateral spines along most of its length; and with no lobe formation. The shell bears bifur cate defensive spines. This record constitutes the first find of an ilyocry ptid in a high altitude crater-lake. This record also increases the number of species known from Mexico to thr ee, and to nine in the New World. Most of the American forms differ from the European ones, such confirming again the non-cosmopolitanism of most of these cladocerans.