海绵动物有不规则、不对称的体制；二层细胞是由中间的凝胶状的间叶细胞分开，内含有变形细胞(阿米巴细胞)、骨针和纤维。
Sponges have an irregular asymmetrical body architecture; there are two cell layers separated by a gelatinous mesenchyme containing amoeboid cells and skeletal spicules and fibers.
生物体各部分的一种排列方式，指沿着中轴的任何平面将生物体分开，所产生的两个部分都是对称的(镜像)。
Radial symmetry the arrangement of parts in an organism in such a way that cutting in any plane across the diameter splits the structure into similar halves (mirror images).
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