它们有一条推进用的尾巴，咽及鳃裂。

Iv. They present a propulsive tail, pharynx and branchial openings.

youdao

它们有一条推进用的尾巴，咽及鳃裂。

Iv. They present a propulsive tail, pharynx and branchial openings.

youdao