Winged stages of Symbiocloeon laoense Palatov 2023 (Ephemeroptera: Baetidae) and systematic position of larvae developing inside mantle cavities of bivalve mollusks

For the first time, imagines were associated by rearing with larvae inhabiting mantle cavities of freshwater bivalve mollusks. This allows us to describe all stages of development of the mayfly species Symbiocloeon laoense Palatov 2023 from Laos and to determine the systematic position of the Oriental genus Symbiocloeon Müller-Liebenau 1979, formerly known as larvae only. Judging by the structure of winged stages, Symbiocloeon belongs to the holophyletic taxon Baetovectata Kluge & Novikova 2011 (or Baetinae in the wide sense), which in its turn, belongs to the holophyletic taxon Anteropatellata Kluge 1997.

Structure of eggs extracted from female S. laoense is characteristic for the subgenus Margobaetis Kang & Yang 1994 of the genus Nigrobaetis Kazlauskas 1987, and analysis of COI MtDNA sequences also suggests close relationship between Symbiocloeon and Margobaetis. If the phylogenetic principle of systematics is accepted, Symbiocloeon can be regarded as a subgenus of Nigrobaetis; in order to avoid changing of the name Nigrobaetis Kazlauskas (in Novikova & Kluge) 1987 to the senior name Symbiocloeon Müller-Liebenau 1979, an application is submitted to the International Commission on Zoological Nomenclature (Case 3959) asking to recognize availability of the senior generic name Nigrobaetis Kazlauskas 1972.

This larval-imaginal association reveals that the former association of the African larvae and imagines described under the name Mutelocloeon bihoumi Gillies & Elouard 1990, was wrong, because these African larvae are related to the Oriental genus Symbiocloeon and, hence, belong to Baetovectata within Anteropatellata, while the imagines of Mutelocloeon bihoumi belong to Rhithocloeonini Kluge 2012 within the plesiomorphon Protopatellata Kluge & Novikova 2011.

Since the holotype of Mutelocloeon bihoumi is a male imago, the species name Mutelocloeon bihoumi and the generic name Mutelocloeon Gillies & Elouard 1990 belong to imagines described under these names. The larvae ascribed to Mutelocloeon bihoumi are moved in the genus Symbiocloeon as an unnamed species Symbiocloeon sp. A. Mutelocloeon bihoumi Gillies & Elouard 1990 is a junior synonym of Mutelocloeon corbeti (Kimmins 1956), syn. nov.; larvae of this species remain unknown.

Possibly, Mutelocloeon Gillies & Elouard 1990 will prove to be a senior synonym of Adnoptilum Gattolliat & Monaghan 2010.