A new sexually dimorphic Diploechiniscus species (Tardigrada: Echiniscidae) from Calvert Island (British Columbia, Canada)

An important, but generally overlooked source in intraspecific variability of characters used in tardigrades taxonomy is sexual dimorphism. Dioecious tardigrades species with unisexual or bisexual populations are common, but external sexual dimorphism is rarely observed. The discovery and integrative analysis of a Diploechiniscus species population with high sexual dimorphism from Calvert Island (Canada) has allowed its description as a new species. Diploechiniscus dimorphus n. sp. is characterized by a different chaetotaxy in males and females, and by enlarged cephalic sensory appendages in the males. The discovery of this new species shows that it is important to consider sexual dimorphism as a source of intraspecific variability in tardigrade taxonomy due to its implications on the use of traits commonly used to delineate species such as chaetotaxy. Lastly, the finding of individuals of Diploechiniscus horningi (Schuster and Grigarick, 1971), a species previously synonymized with Diploechiniscus oihonnae (Richters, 1903), allows us to prove that it is genetically a separate species and to reinstate it.