Haeckel, 1880
Atollidae with the characters of the family, to which may be added: gonads 8, adradial; rhopalia 8; disk quite flat, mesoglea of central region lens-shaped; coronal groove deep. The four accepted species are notably uniform in appearance. Just the commonest species is therefore described in detail, and the discriminating characters of the other three species summarised afterwards.
Atolla wyvillei
Atolla chuni
Atolla parva
Atolla vanhoeffen