The cave hygropetric - a little known habitat and its inhabitants

While rocks are generally dry on the surface if they are not permanently wetted, most walls in caves are permanently moist or wet. Therefore, it is reasonable to apply and restrict the term cave hygropetric to the habitat which offers its potential inhabitants special conditions and/or requires special adaptations. Such are the cave walls with thin water films moving down in mostly laminar flow, a moderately common phenomenon in karst caves. Some conspicuously troglomorphic leptodirine beetles (Coleoptera: Cholevidae: Leptodirinae) in caves along the Dinaric and Italo-Dinaric karst between W Montenegro and NE Italy regularly occur in such places. They belong to genera Tartariella NONVEILLER & PAVICEVIC 1999, Hadesia MUELLER 1911, Nauticiella MORAVEC & MLEJNEK 2002, Radziella CASALE & JALIC 1988, Cansiliella PAOLETTI 1972. These beetles may be associated with some relatively generalist troglobionts, including the predaceous amphipod Typhlogammarus mrazeki SCHAEFERNA in Hercegovina, the predaceous leech Croatobranchus mestrovi KEROVEC, KUCINIC & JALZIC in the Velebit Mountains, and the detrivorous oniscid isopod Illyrionethes sp. Although not very closely mutually related, the hygropetric leptodirines are similar in shape (pholeuonoid), with enlarged and curved claws, and with modified mouthparts, characterized mainly by a marked setation and by knee-shaped mandibles. Similar set of morphologies occurs in three unrelated groups of semiaquatic Diplopoda, as well as in some aquatic Crustacean genera (Isopoda: Asellidae; Amphipoda: Niphargidae). Such modified mouthparts evidently mostly occur in the nutrient-poor hypogean habitats, where alternative feeding modes may be of a particular advantage.