The first species of Thelastoma Leidy, 1849 (Nematoda: Thelastomatidae) parasitising the scorpion Euscorpius italicus (Chactidae: Scorpionidea).

A new species, Thelastoma euscorpii, (Thelastomatidae: Oxyuroidea) is described from Euscorpius italicus (Chactidae) on Pag Island (Kvarner Islands), Croatia. The new taxon differs from all other species of Thelastoma in having a cuticle with fine transverse striae. The excretory pore of the female specimens is located in a prebulbar position, the tail is short and subfiliform (5.5-9.3% of the total body length), and the eggs are small (47-52 x 24-29 microm). The males have a short oesophagus and no spicules. This is the first nematode species found in scorpions (Scorpionidea).