棘皮动物门是动物界的一门。这个门从寒武纪出现，总共有20000多种类，现生种约5000余种。除现生5纲外，另有15纲之多，皆为海生动物，无陆生或淡水种类。常见的海胆与海参皆属于此门。

棘皮动物是后口动物。它们的原肠胚孔形成肛门，而口部是后来形成的。它们有特殊的五体对称步管结构。棘皮动物的次生体腔发达，是由肠体腔（enterocoele）发育形成。

由于棘皮动物在胚胎形成方式及DNA串行上与脊索动物相似，被认为是包括人在内的脊索动物的近亲。

棘皮动物特有的结构是水管系统和管足。

刚出生的棘皮动物是两边对称的。成长期间，左边增大而右边缩小，直到右边被完全吸收了，然后这一边长成五倍辐形对称形状。

Echinoderm is the common name given to any member of the Phylum Echinodermata (from Ancient Greek, ἐχῖνος, echinos – "hedgehog" and δέρμα, derma – "skin") of marine animals. The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.