Sea cucumbers are members of the phylum Echinodermata, along with sea urchins, starfish and other radially symmetrical, " spiny-skinned" marine invertebrates.
海参是棘皮动物门的成员，还有海胆、海星和其他径向对称的“多刺”海洋无脊椎动物。
Radially symmetrical
原声例句
TED-Ed（视频版）
PBS地球-动物趣闻
The first radially symmetrical echinoderm known from the fossil record is Camptostroma, which showed up between 516 and 513 million years ago in Pennsylvania.
化石记录中已知的第一个径向对称棘皮动物是 Camptostroma，它出现在 516 到 5.13 亿年前的宾夕法尼亚州。
英语百科
Symmetry in biology
Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism. In nature and biology, symmetry is always approximate: for example plant leaves, while considered symmetrical, rarely match up exactly when folded in half. Symmetry creates a class of patterns in nature, where the near-repetition of the pattern element is by reflection or rotation. The body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. A small minority, notably among the sponges, exhibit no symmetry (i.e., are asymmetric).