''Acaulis'' is a genus of

hydrozoan Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial sp ...

s that typically lives in polar environments but is known to have been observed in subtropical and boreal regions. Its only species is ''Acaulis primarius''. They are said to range in depth from below sea level, and also reproduce asexually.

References

Acaulidae Taxa described in 1853 Taxa named by William Stimpson Monotypic cnidarian genera {{Anthoathecata-stub