Paralovricia beroni is a new species. Scale bar: 1 mm. Credit: Pensoft Publishers

One of the smallest ever cave-dwelling ground beetles (Carabidae), has recently been discovered in two caves in the Rhodopi Mountains, Bulgaria, and described under the name Paralovricia beroni. The beetle is completely blind and is only 1.8-2.2 mm long. The study was published in the open access journal ZooKeys.

"When we saw this beetle for first time, it became immediately clear that it belongs to a genus and species unknown to science. Moreover, its systematic position within the family of Carabidae remained unclear for several years. After a careful study of its closest relatives Lovricia and Neolovricia, discovered in caves of the Dinaric Alps of Croatia, we came to the conclusion that all three genera belong to a new subtribe which we describe now under the name Lovriciina", commented Borislav Gueorguiev from the National Natural History Museum in Sofia, Bulgaria.

The species of this group are extremely rare and are known only from a few specimens. Lovricia jalzici was described in 1979 which is presently known only from a single female specimen found at the cave Gospodska pećina in Croatia; Lovricia aenigmatica is known from one male and one female found at an unnamed pit near the peak Sveti Jure on the Biokovo Mountains and from another female from Lovrićija Jama II (Sveti Jure, Biokovo); lastly, Neolovricia ozimei was described also very recently (2009), and is known from one female found in the cave Åpilja u Radinovcima in the Biokovo Mountains, Croatia.

The new discovery sheds light on the paleogeographic history of the Balkans. The currently known distribution of this group of beetles with common origin is widely disjointed between the Dinarides (West Balkans) to the Rhodopes (Еast Balkans).

"To explain this" - adds the lead author Pier Ðœauro Ciachino, from Torino, Italy - "we must go back at least to the Late Oligocene (29-24 million years) where a continuum of land connected the Dinarides and Rhodopes mountains, allowing colonization by this phyletic lineage. Conversely, a paleogeographic event that could be placed at the origins of the separation of Paralovricia (in the Rhodopes) from a common ancestor - which then enabled a further differentiation of Lovricia and Neolovricia in the Dinarides - may be identified in the Early Miocene (20.5-19 Ma) when a strip of lowlands, covered with freshwater lakes and marshes seems to have divided the Dinarides from the Rhodopes."

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