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