2–25 mm long transparent worms that are very common in fresh water and often form chains of individuals through asexual multiplication.

Externally, the animals correspond to the general building plan of the Naididae, however, in distinction from the other species, they bear setae (bristles) only on their ventral side, which is what gives them their name.

These worms occur mostly in stagnant or flowing freshwater, but the largest species, Chaetogaster diaphanus, also lives in brackish water.

diaphanus consumes organisms in the size class of about 0.3–3 mm, which mostly contains zooplankton (rotifers, water fleas etc.

The unselective nature of their feeding is clearly shown by the fact that sand grains and other indigestible particles (e.g. conifer pollen) are always found in their stomachs.

l. limnaei) attaches itself externally to the body of snails or to the inside of their shell (Lymnaea, Physa, Ancylus, Australorbis and many other genera[3]) and can freely move (so-called commensal ectosymbiosis).

These chains give rise to new individuals through division (paratomy), which have, because of the asexual nature of the multiplication, the same genetic blueprint as the original worm.

[9] The membership of the genus Chaetogaster to the family Tubificidae and the subfamily Naidinae has meanwhile been confirmed not only on morphological but also on molecular-genetic grounds.