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

• 无体腔动物：没有体腔的动物。无体腔动物包括扁虫、吸虫、绦虫或纽虫。为两侧对称，有一内部消化腔