The document summarizes key concepts about the evolution of animal diversity. It describes the major splits in animal evolution including acoelomates vs coelomates, radiates vs bilateria, and protosomes vs deuterosomes. The Cambrian explosion occurred around 500 million years ago, resulting in the emergence of modern animal phyla. Today's animals can be classified into over 35 phyla based on their adult forms, embryological development, body symmetry, and presence of tissues and body cavities. Examples of major phyla include sponges, cnidarians, flatworms, arthropods, mollusks, and chordates.

1. AP Biology - Core Concept Cheat Sheet
16: The Evolution of Animal Diversity
Animal Evolution
Animal Features
• Acoelomate vs coelomate split: acoelomates-animals
with no coelome (body cavity). Coelomates-all animals with
a body cavity
• All surviving animals today can be traced back to their
ancestors to this time period. Major advance in animal
evolution is sudden appearance of hard tissues in animalsabout 550 million years ago.
• Animal Diversity: Animal diversity expanded because of
increased dependency on the predatory /prey relationship,
adequate environment oxygen to support active animal life
style, development of genes to assist embryonic
development.
• Animal organs: most animals have a body form, muscle,
hormones, circulatory, respiratory, excretory skeleton,
nervous and sensory systems
• Animal: eukaryotic, multicellular heterotrophs without cell
wall
• Cambrian explosion: About 500 million years ago, extant
animal body plans were identified on fossil records
• Characteristics of animals: eat other organisms, able to
absorb, digest and excrete food. Can store energy as
glycogen, utilize collagen as a basic structural protein, are
diploid, reproduce sexually, have the ability to develop
motile sperm and non motile eggs, develop from embryos
and posses nervous and muscle tissue
• Features of animals: go through embryonic stages that
include the blastula and gastrula. Have distinct types of cell
junctions. Are composed of diploid cells with the exception
of gametes. Contain genes that regulate zygote growth
• Gastrulation: gastrulation is defined as the mode of
animal development which leads to differentiation of animal
tissues into germinal layers
• germ layers: Ectoderm- becomes the outer surface and
nervous tissue of animals, Mesoderm-becomes muscle,
skeletal and connective tissue, Endoderm- becomes the
lining of the digestive gut
• Invertebrates: the majority of animals are invertebrates;
extant animals are divided into about 35 phyla.
• Parazoa vs eumetazoa split: earliest split in evolution
was between parazoa and eumetazoa- animals
lacking/possessing true tissues. Phylum porifera are the
only extant members of the parazoans.
• Phyla groups: phyla are grouped according to their adult
and embryological forms. The different phyla were split
millions of years ago. The major splits were among:
parazoa vs eumetazoa, radiate vs bilateria, diploblastic vs
triploblastic, acoelomates vs coelomates, protosomes vs
deuterosomes
• Protosomes vs deuterosomes split: organisms in whom
a second opening serves as the mouth are protosomes;
organisms in whom the second hole serves as the anus are
deuterosomes.
• Radiata vs bilateria split: radiata are those animals with
radial symmetry and are diploblastic (eg cnidaria). Bilateria
are all other animal groups which are bilateral symmetric
and are triploblastic.
• Advantages of coelome: animals have room for growth of
internal organs, can have a circulatory system, fluid itself
can act as a transport system, the muscles can squeeze fluid
and the digestive tract muscles are independent of body wall
muscles
• Acoelome: animals with no body cavity, such as phylum
platyhelmenthyes (flatworms)
• Pseudocoelomates: have a “false gut cavity”, eg
nematode. The have no segmentation and no muscles
around the digestive tract. Roundworms are classified in the
phylum, nematode.
• Cambrian explosion: modern phyla evolved during the
Cambria period-about 500 million years ago. This was a 10
million year period of explosive evolution. No new animal
species have been discovered after the Cambrian explosion
and it appears that all phyla have been locked in
• Sponges: phylum porifera: marine animals built on a
body plan with a radial symmetry- ie have similar shapes as
mirror images
• Cnidaria: exhibit radial symmetry. Body plans have a
central tubular body surrounding a gastrovascular opening
• Platyhelmenthes: flatworms with a gastrovascular cavity
and no other body cavity. The body has a head end with
sensory nerves.
• Arthropod: most successful of all phyla. Are segmented,
have jointed appendages and have an exoskeleton composed
of chitin
• Segmentation: segmentation is subdivision of body in
repeat parts. Earthworms have repeating segments.
Segmentation provides body flexibility and mobility
• Mollusks: Have a common body plan with bilateral
symmetry with a complete digestive tract, coelom and
internal organs. Have a muscular foot and mantle. The
outgrowth of the body surface functions as a shell, sensory
organ and houses gills
• Human and Animal diversity: The introduction of non
native animals into new environments may result in the
death of the species or the survival of the species and
destruction of the ecosystem.
Origin of Animal:
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