The protostomes split into two lineages

Developmental, structural, and molecular data all suggest that the proto-stomes soon split into two major lineages that have been evolving independently since an cient times: lophotrochozoans and ecdysozoans. Lophotrochozoans, the animals we will discuss in the remainder of this chapter, grow by adding to the size of their skeletal elements. Some of them use cilia for locomotion, and many lineages have a type of free-living larva known as a trochophore (see Figure 32.23) The phylogeny of lophotro-chozoans we will use in this chapter is shown in Figure 32.14. In contrast, ecdysozoans, the animals we will discuss in the next chapter, increase in size by molting their external skeletons. They move by mechanisms other than ciliary action, and they all have a common set of homeobox genes.

32.14 A Current Phylogeny of Lophotrochozoans Three major lineages, including the lophophorate and spiralian phyla, dominate the tree. Some small phyla are not included here.

Three embryonic cell layers

Lopho-trochozoan ancestor

32.14 A Current Phylogeny of Lophotrochozoans Three major lineages, including the lophophorate and spiralian phyla, dominate the tree. Some small phyla are not included here.

Three embryonic cell layers

Lopho-trochozoan ancestor

Three Major Cellular Lineages

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  • felicia martinez
    What are the two major lineages of the protostomes?
    8 years ago
  • MYRTLE
    What are the two divergent lineages that projaryotes split into early in history of life?
    6 years ago

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