海蜘蛛，是节肢动物海蜘蛛纲海蜘蛛目的总称，因形似蜘蛛，故名。

• 体长5-6毫米，褐色或淡黄色；
• 头胸部前端有口，上面有4个小隆起，上面有单眼；
• 腹部不发达，为一小突起；
• 头胸部有4对长足，末端有钩爪，前方有一对小螯肢。

Sea spiders, also called Pantopoda or pycnogonids, ('pycno-' closely packed, 'gonid' gonidia) are marine arthropods of class Pycnogonida. They are cosmopolitan, found especially in the Mediterranean and Caribbean Seas, as well as the Arctic and Antarctic Oceans. There are over 1300 known species, ranging in size from 1 millimetre (0.039 in) to over 90 cm (35 in) in some deep water species. Most are toward the smaller end of this range in relatively shallow depths, however, they can grow to be quite large in Antarctic waters.