Redescription of Chirocephalus bobrinskii (Alcock, 1898) (Anostraca: Chirocephalidae) with special attention to somatic sensillar armature

Systematics within the Chirocephalidae (Branchiopoda) remain confused at the genus level and in several groups within Chirocephalus. We redescribe Chirocephalus bobrinskii (Alcock, 1898), an endemic of Central Asia, based on material from several localities in Tajik Pamir, Tajikistan. The studied populations displayed significant variability of the second antenna distal antennomere, shape and size of the antennal appendage, and thoracopods, but only slight interpopulation genetic variation of the Folmer’s COI gene fragment. With such high morphological plasticity, no clear quantifiable differences were observed between C. bobrinskii and the closely related Central Asian taxa, C. altaicus Daday, 1910 and C. turkestanicus Daday, 1910, which we treat as junior synonyms. Based on morphological and genetic evidence, C. bobrinskii likely belongs to the C. spinicaudatus group, but further integrative revision of that group is needed. We also discuss the structure and location of somatic sensillae in C. bobrinskii, which differ between sexes. As these sensory structures are present in many anostracans and may have specific patterns in different groups, they may be useful in systematics. Unfortunately, the somatic sensillae are rarely included in species descriptions due to their small size. Thus, more studies are needed to clarify the significance of sensillar morphology to anostracan taxonomy.