A bizarre creature which looks like a bootlace or black string was caught by a stunned fisherman who had no idea what it was and shared it on social media.
The dark-coloured, wiry creature moves with a distinctive snapping motion as it jerks around on top of some rocks.
The incident was filmed at Zavoj Lake on the Visocica River in south-eastern Serbia and the footage was later posted on Facebook by Marko Ungurjanovic where it has been widely shared by baffled viewers.
Marko said the little creature was accidentally hooked while fishing at the lake.
While he did not know what the organism was, he later discovered that it was a Nematomorpha, commonly known as horsehair worms or Gordian worms.
Most species range in size from 5 to 10 centimetres, sometimes reaching lengths of up to two metres in extreme cases.
Despite this extreme length, the worms are usually between one and three millimetres in diameter.
Horsehair worms are found in damp areas, such as watering troughs, swimming pools, streams, puddles, and cisterns.
While the adult worms are free-living, the larvae live as parasites on creatures such as beetles, cockroaches, mantids, and crustaceans.
They have an external cuticle without cilia (a hair-like organ) and inside, the weird animals have only a longitudinal muscle and non-functional gut.
This comes after a grotesque looking sea monster which resembled a human brain was found washed up on a beach.
And a “mutant” sea animal with disturbing human-like features caused panic when it was found alive after being brought ashore by the tide.
Meanwhile, the skeleton of a sea creature with fangs on its tail baffled a woman when she stumbled upon its remains at the beach in Brighton.
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