在海洋中生存着一种无脊椎动物,它就是海胆,别名刺锅子、海刺猬,体形呈圆球状,就像一个个带刺的紫色仙人球,因而得了个雅号——“海中刺客”。渔民们也常把它称为“海底树球”、“龙宫刺猬”。在遥远的过去(古生代和中生代时期),海胆有很多种类,仅发现的海胆化石就多达5000余种。海胆的身体由一个球形或盘形的胆壳所包围,生物学家称为硬壳,壳上布满了许多刺样的东西,叫做棘,可千万不要小瞧这些棘,它们可是有 There is an invertebrate living in the ocean. It is the sea urchin, which is named after the sea urchin. It has an oval ball shape, like a prickly purple cactus, and it has a nickname—“Sea Assassin”. Fishermen often refer to it as “submarine tree ball” and “dragon hedgehog.” In the distant past (Paleozoic and Mesozoic), there were many species of sea urchins, and as many as 5,000 sea urchin fossils were discovered. The body of the sea urchin is surrounded by a spherical or disk-shaped bile. Biologists call it a hard shell. The shell is covered with a lot of spiny-like things called spines. Don’t underestimate these spines. They have