Although they have specialized cells for particular functions, they lack true tissues in which specialized cells are organized into functional groups. Sponges appear to represent an early stage of multicellularity in the animal clade. The sponges and the cnidarians represent the simplest of animals. Invertebrates include a huge diversity of animals, millions of species in about 32 phyla, which we can just begin to touch on here. Although in general we are most familiar with vertebrate animals, the vast majority of animal species, about 95 percent, are invertebrates. The kingdom of animals is informally divided into invertebrate animals, those without a backbone, and vertebrate animals, those with a backbone. Describe the organizational features of cnidarians.Describe the organizational features of the simplest animals.By the end of this section, you will be able to:
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