Gastrotricha, hairy-backs

Gastrotricha have/are

An outer cuticle and ventral cilia
Bilaterally symmetrical and worm-like
A body covered in spines, hooks and adhesive tubes
A through gut and anus
A nervous system and two longitudinal cords
Hermaphrodite or parthenogenic
Aquatic, freshwater and marine

Don't have

A body cavity
Circulatory or gaseous exchange systems

Greek: gaster = stomach, thrix = hair

Gastrotrichs (hairy-backs) are small (less than 4 mm), dorsoventrally flattened, transparent worms. At the anterior end they have sensory bristles, cilia, sensory pits, and some species have eye spots. The body ends in a tail or fork. Over 400 species are known, among these 50 freshwater species are found in the U. K.

Chaetonotus, Gastrotricha

They inhabit interstitial spaces in sand and compacted surfaces, and move using epidermal cilia to glide along, or loop in a leech-like fashion using adhesive tubes, see Chaetonotus sp. above and below which has two adhesive tubes.


Males tend to be rare and poorly developed.The marine species tend to be less well known, but their food is the same as all Chaetonotus sp.

Chaetonotus maximus, Gastrotrich

Above is Chaetonotus maximus, a freshwater gastrotrich. Chaetonotus sp. feeds on detritus, bacteria, diatoms and protozoa.