The width of the shell is 5–12 mm. The height of the shell is 10–22 mm.
Ecology
It lives in calm pools of fast-flowing streams and also on rocks in small waterfalls. Polgar et al. measured thermal tolerance of Clea nigricans. The behaviour of Clea nigricans in natural habitat is unknown.
Like all snails in the clade Neogastropoda, this species is carnivorous. It feeds on different types of worms and gastropods, often eating other, larger snails after burying themselves and ambushing their prey.
Life cycle
Clea nigricans consists of defined male and femalegenders, and is not capable of gender change. It is unknown as to how to sex these animals. Both males and females seem to be the same size and shape. When a male and female mate, they lock together for 8–12 hours.