Abstract
The new freshwater leech species Helobdella nahuelhuapensis is described based on the examination of 17 specimens collected near Nahuel Huapi Lake, Bariloche, Argentina with following diagnostic characters. Body thin and lanceolate. Chitinoid scute absent. Unpigmented region (nuchal gland) at somite VIII. Annuli subdivided dorsally. Dorsum surface lacking both papillae and tubercles. One pair of eyes on somite III; mouth pore in the anterior margin of the oral sucker; proboscis base at XII/XIII, diffuse parenchymal salivary tissue; oesophagus simple; crop with gastric chambers; postcaeca or diverticula extending posteriorly; intestine with four caeca. Six pairs of spherical testisacs; sperm ducts reach to somite XV/XVI. Atrium pyriform without preatrial loops. Ovisacs simple, reaching XIV.
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