Among animals with a body cavity, there are differences in how the cavity develops. If the cavity is not completely lined by tissue derived from mesoderm, it is termed a pseudocoelom. Animals with this body plan, such as rotifers (phylum Rotifera), roundworms (phylum Nematoda), and a few other phyla, are called pseudocoelomates (FIGURE 29.4b). Coelomates are animals with a true coelom, a fluid-filled body cavity completely lined by tissue derived from mesoderm. The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally to form mesenteries, which suspend the internal organs (FIGURE 29.4c).
Among animals with a body cavity, there are differences in how the cavity develops. If the cavity is not completely lined by tissue derived from mesoderm, it is termed a pseudocoelom. Animals with this body plan, such as rotifers (phylum Rotifera), roundworms (phylum Nematoda), and a few other phyla, are called pseudocoelomates (FIGURE 29.4b). Coelomates are animals with a true coelom, a fluid-filled body cavity completely lined by tissue derived from mesoderm. The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally to form mesenteries, which suspend the internal organs (FIGURE 29.4c).
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