Pigmented, with two eyes, each composed of several pigment cells and numerous retinal cells. Head typically of low triangular form, with definite auricular slits. Pharynx usually free of pigment. Testes numerous, dorsal (except N. tinga) and not extending beyond copulatory apparatus. Seminal vesicle a single muscular cavity. Ejaculatory duct typically convoluted, usually with a proximal glandular chamber, and without a diaphragm. Bursa copulatrix present anterior to penis. Bursal stalk musculature of inner longitudinal fibres surrounded by a thick layer od circular fibres, particularly ectally. Oviducts enter bursal stalk above zone of shell glands. Cocoon so far as known, unstalked. Inhabitants of freshwater.