acoelomate

n.
An animal that lacks a coelom. Acoelomates, which include the flatworm, fluke, tapeworm, and ribbon worm, exhibit bilateral symmetry and possess one internal space, the digestive cavity.

[New Latin Acoelōmata, group name : A-¹ + Greek koilōma, koilōmat-, cavity; see coelom.]

acoelomate a·coe'lo·mate (-lə-mĭt) adj.