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Chapter 31 Animal Origins & the Evolution of Body Plans
31.1 What Evidence Indicates the Animals Are Monophyletic
Traits that distinguish animals from other groups:
- Unlike bacteria, archae, and most microbial eukaryotes, all animals are multicellular. Animals develop from single-
celled zygote into a multicellular adult.
- All animals are heterotrophs.
- Fungi are also heterotrophs, but unlike fungi, animals use internal processes to break down materials from
environment into organic molecules they need most.
- They can move.
Animal Monophyly:
- may have resembled modern choanoflagellates, protists that are closest living relatives of animals
Proof of Animal Monophyly:
- Gene sequence, such as the ribosomal RNA genes.
- Organization and function of Hox genes that are present in all animals.
- Types of junctions between cells that are present in all animals.
- Animals have a common set of extracellular matrix molecules, ex. Collagen & proteoglycans
Embryonic develop wrt phylogeny:
- First few cell division of zygote = cleavage (# of cells doubles)
- Different cleavage patterns exist amongst different animals.
- During early development of animals, distinct cell layers form, which later develop into organs and
organ systems.
- The embryos of diploblastic animals have 2 of the cell layerouter (called ectoderm) and inner
(called endoderm).
- The embryos of triploblastic animals have above 2 and a 3rd layer (called mesoderm) which lies
between the other 2.
- During early development, a hollow ball indents to form a cup-shaped structure, process =
gastrulation.
- The opening of the cavity formed by this indentation is called the blastopore. The pattern of formation after the
appearance of the bastopore divides the triploblastic animals into 2 main groups: protostomes and deuterostomes.
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Document Summary

Chapter 31 animal origins & the evolution of body plans. 31. 1 what evidence indicates the animals are monophyletic. Unlike bacteria, archae, and most microbial eukaryotes, all animals are multicellular. Animals develop from single- celled zygote into a multicellular adult. Fungi are also heterotrophs, but unlike fungi, animals use internal processes to break down materials from environment into organic molecules they need most. May have resembled modern choanoflagellates, protists that are closest living relatives of animals. Gene sequence, such as the ribosomal rna genes. Organization and function of hox genes that are present in all animals. Types of junctions between cells that are present in all animals. Animals have a common set of extracellular matrix molecules, ex. First few cell division of zygote = cleavage (# of cells doubles) Different cleavage patterns exist amongst different animals. During early development of animals, distinct cell layers form, which later develop into organs and organ systems.

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