Abstract
The genus Cymbalcloeon gen. nov. (Ephemeroptera: Baetidae) is established for a new species Cymbalcloeon sartorii sp. nov. from Thailand, based on larval stage. This genus is unique among all of the Baetidae by the presence of three pairs of single gills on segments V–VII, ventrally oriented to cover the sterna VI–IX. Cymbalcloeon sartorii gen. nov. et sp. nov. presents unique or rare morphological characters such as a deeply concave margin between the prostheca and mola, without setae; a very large subtriangular process of the left mandible; a maxillary palp segment II with scarce and very long setae; almost completely fused labial palp segments II and III with numerous very long setae; elongate tarsal claw with two rows of teeth; a shagreen surface of the terga and paraproct; and a very reduced body size. The gills of the new genus move very quickly during respiration and present a near-synchronous protraction. Due to the very derived larval morphological character and the unknown imaginal stage, the exact phylogenetic position of the genus remains unclear; it most certainly belongs to the concept of Anteropatellata and is possibly closely related to the genus Baetopus.
Highlights
The family Baetidae is the most diverse family among mayflies, comprising 1,070 species in 110 genera [1, 2]; this accounts for about 30% of all mayfly species worldwide
The number of studied species in this family in Southeast Asia has steadily increased in the last decade, with about 45 species and 4 new genera described from this area
We describe an incredible new genus of the family Baetidae from Thailand based on larval stage only
Summary
The family Baetidae is the most diverse family among mayflies, comprising 1,070 species in 110 genera [1, 2]; this accounts for about 30% of all mayfly species worldwide. The number of studied species in this family in Southeast Asia has steadily increased in the last decade, with about 45 species and 4 new genera described from this area. Most of these mayflies have been reported from islands. Procerobaetis Kaltenbach & Gattolliat, 2020 is the last described genus of Baetidae, with 3 new species from Southeast Asia, discovered in the Philippines and Indonesia [6]. The number of species known from this area most certainly remains much lower than the real diversity [7]
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