The Cave tube-worm (Marifugia cavatica) inhabits the underground freshwater of the Dinaric karst (mountain range from Italy to Albania). It is the only known representative of the Serpulidae family that lives in caves. Scientists assume that 5.3 – 2.6 Ma ago, during the Pliocene, species lived in lakes on the surface.
The Cave tube-worm is a sessile animal. It lives attached to the cave walls and builds a limestone tube up to 6 cm long around the worm-like body. Through the tube, it draws out feathery crown of tentacles that filter the organic substance from the water. In unfavorable conditions, such as drought, the entire body can be drawn into the tube and closed with the lid. It inhabits water within a temperature range from 4 to 19 °C, and can build dense colonies in places with slower water flow. Such colonies make a special habitat – a community of marifugia deposits in which many other aquatic cave animals live.
Leeches (Hirudinea) are class within the annelids (phylum Annelida). Several species of leeches occasionally inhabit caves, but real cave species (stigobionts) are rare. Most of the stigobiotic leeches belong to the Erpobdellidae family. In Europe, stigobiotic leeches belong to the genus Dina and maybe Trocheta. For confirmation of Trocheta genus, further research is needed. Adaptation of leeches to life in caves are milky white to pink body color, lack of eyes or eye pigment, and sometimes a wider anterior sucker.
In Croatia, in the caves of Istria and Lika regions, we find a stygophilic species Dina krasensis. From the stigobionts, Absolon’s leech (D. absoloni) lives in the Dalmatia region, while the deep caves of northern Velebit Mt host the Meštrov’s leech (Croatobranchus mestrovi).
Not much is known about the biology of the C. mestrovi. The species has so far been found only in four deep pits in northern Velebit Mt (cave system Jamski sustav Velebita, cave system Jamski sustav Lukina jama – Trojama, and caves Slovačka jama and Jama Olimp). Most of the specimens were found in the hygropetric zone or in drip pools with a water flow and temperatures from 4 to 6 °C. They are often found attached to a cave wall in a weak water flow with their heads facing the water stream as they actively move.
Adult specimens are 25 – 40 mm in length, with an elongated body and slightly dorsoventrally flattened. Their body is milky white to slightly yellowish in colour, without eyes. The most obvious difference from other leeches are finger‐like lateral projections. Their proper functions are not fully clarified, but it is assumed they serve for oxygen supply which in leeches occurs through the surface of the body. It is assumed the species is predatory, like its relatives living outside of caves, but there is no concrete evidence of its diet.