The body is cylindrical, elongated in length, with pointed front and rear ends. Size from 0.3 to 10 mm. Due to the ability to reproduce asexually (see below), the body, as a rule, is a chain of non-separated individuals ( zooids ), the length of one zooid does not exceed 1.5-2 mm.
The mouth, like all representatives of the order Macrostomida, is located on the front end of the body.
Near the front end on the sides there are two red eyes (sometimes they are absent). Behind them, also on the sides of the body, are two ciliary fossae (a sign of the Microstomidae family). Under them, on the lower side of the body, are paired excretory pores, and behind them is the oral opening. The mouth leads to the throat, and that, in turn, into the intestine, which occupies almost the entire body of the worm.
The body is colorless or painted a faint yellow, brown, grayish color. The parenchyma is transparent, but the intestine, filled with food, is usually dark in color and makes the body almost opaque.
The worm epithelium contains the so-called kleptocnids - stinging capsules of hydra eaten by it.
It is capable of asexual reproduction by transverse division ( paratomy ), with the formation of chains consisting of undivided individuals in an amount of up to 23 pieces, between which there are partitions. Asexual reproduction occurs throughout the summer, sexual - only in the fall.
Predator. It feeds on worms, small crustaceans and hydra. If you enter a tank that contains hydra, it can cause great damage. Very widespread, common in fresh standing water bodies.