New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera) Author Prokin, Alexander A. Author Petrov, Pyotr N. Author Wang, Bo Author Ponomarenko, Alexander G. text Zootaxa 2013 3666 2 137 159 journal article 10.11646/zootaxa.3666.2.2 930d392c-8720-4820-85eb-501985209cf3 1175-5326 220466 1F8D4E8A-2447-4556-9B98-D8229D858194 Family Liadytidae Ponomarenko, 1977 Diagnosis (modified from Ponomarenko 1992, English translation of Ponomarenko 1977): Medium-sized aquatic beetles with oval, biconvex body. Head noticeably retraced into prothorax, scutellum visible. Mesocoxae located close to each other. Metepisterna reaching mesocoxal cavities. Metaventrite without anteromedial process protruding between mesocoxae, medially with elevated area sharply limited laterally. Anterior margin of metacoxae forming small median emargination bounded in front by extension of transverse metaventral suture. Legs slender and long. Metatibia not shorter than metafemur and metatarsus, very slender, linear. Tarsal segments not broad or paddle-shaped. Tibiae and tarsi with swimming setae. Notes : A broad lateral part of the metathoracic praeepisternum, a metathoracic anepisternum that reaches the mesocoxal cavities, and a transverse suture of the metaventrite characterize only two known families of Dytiscoidea: Liadytidae and Aspidytidae , the only observable difference between which listed by Balke et al. (2003) is the absence of swimming setae in Aspidytidae . This character is, in fact, insufficient for distinguishing between families of Dytiscoidea, because the families Noteridae , Dytiscidae and Coptoclavidae include members that vary in the state of this character. The characters most clearly distinguishing Aspidytidae from the other Dytiscoidea, configuration of the scapus and pedicellus (Ribera et al . 2002), are not discernible in the known species of Liadytidae . The new species Liadytes aspidytoides sp. n. is placed here in Liadytidae , based on the age of the fossils and on their mesocoxae located close to each other and the absence of the anteromedial metaventral process. This character distinguishes all Liadytes from all Aspidytes Ribera, Beutel, Balke & Vogler, 2002 and is reported here for the first time. Since Liadytes and Aspidytes are the single genera in the respective families, we can use this character also for distinguishing between the Liadytidae and Aspidytidae . The monotypic genus Ovidytes and species O . gaoi Ren, Zhu & Lu, 1995 were described in the family Liadytidae (Ren et al. 1995) . We could not study the type material of this species, but judging by the relatively short non-swimming legs, shown in an illustration to the original description, O . gaoi can hardly belong to Dytiscoidea.