A new subterranean Maraenobiotus (Crustacea: Copepoda) from Slovenia challenges the concept of polymorphic and widely distributed harpacticoids

Maraenobiotus slovenicus sp. nov. is described from subterranean waters of a very cold, temporary karstic spring in the vicinity of Velika Pasica cave, central Slovenia. A detailed examination of numerous specimens reveals a low level of morphological variability in this population. Morphological characters traditionally used in the genus Maraenobiotus Mrázek, 1893 would identify our population as a subspecies of the polymorphic and widely distributed M. vejdovskyi Mrázek, 1893. This species was reported from the Palearctic, with at least six accepted subspecies, some of which have been reported in sympatry or parapatry, sometimes even without any apparent niche partitioning. One of these subspecies, M. vejdovskyi truncatus Gurney, 1932, originally described from the UK and later on also reported from Italy and Japan, shares with our population the extremely reduced female principal caudal setae. However, a closer examination of the caudal armature and other characters reveals significant differences between these disjunct populations. We propose a hypothesis of distinct species within the M. vejdovskyi-complex, and critically review all recognized and some unrecognized morphotypes and subspecies. As a result, three new species names are proposed for previously reported populations from Italy and Japan: Maraenobiotus galassiae sp. nov.; M. isidai sp. nov.; and M. pescei sp. nov. Four subspecies of M. vejdovskyi are now elevated to the full specific rank: M. anglicus Gurney, 1932; M. arctica Löffler; M. tenuispina Roy; and M. truncatus Gurney, 1932. This hypothesis remains to be tested using molecular (and other) tools, but can serve as a viable alternative to the concept of polymorphic and widely distributed freshwater harpacticoids.