introduction to animal evolution
Transcript introduction to animal evolution
Introduction To Animal
• Animals 1st appeared in Precambrian
in waters, spread to land.
• 5 criteria that define animal:
• 1Animals multicellular, must get
food through ingesting other
organisms or organic material.
• 2Animals do not have cell walls.
• 3Animals have nervous tissue to
conduct impulses and muscle tissue
• 4Most animals reproduce sexually
with diploid stage being dominate.
• 5Animals have special regulatory
genes (Hox genes) help zygote form
Branching of evolutionary tree
• 1st branch point splits Parazoa (lack
true tissues) from Eumetazoa (true
• Parazoa include sponges.
• Eumetazoans divided into 2 major
branches, partly based on body
• Radial symmetry - phylum Cnidaria
and phylum Ctenophora.
• Bilateral symmetry (left and right
side) - rest of phyla.
• Bilateral symmetry - cephalization,
- concentration of sensory
equipment towards head.
• Difference between 2 groups presence of germ layers - layers of
embryonic tissue that form various
tissues and organs.
• Bilaterally symmetric animals - 3
germ endoderm (innermost),
mesoderm (middle) ectoderm
• Bilateral animals split according to
presence of body cavity (fluid-filled
space separating digestive tract
from outer body wall) and what
cavity looks like.
• Acoelomates (phylum
Platyhelminthes) have solid body,
lack body cavity.
• Some organisms - body cavity - not
completely lined by mesoderm.
• Pseudocoelomates include rotifers
(phylum Rotifera), roundworms
• Coelomates organisms with true
coelom, (fluid-filled body cavity
completely lined by mesoderm).
• Body cavity has many purposes
including cushioning organs, allowing
them more room to grow.
• Coelomate phyla divided based on
differences in development.
• Many protostomes (mollusks,
annelids, arthropods) undergo spiral
• In many protosomes, blastopore
develops into mouth; 2nd opening at
opposite end of gastrula develops
• Zygotes of many deuterostomes
undergo radial cleavage.
• Deuterostomes - blastopore usually
develops into anus, mouth derived
from 2nd opening.