Intro to Animal DiversityChapter 32

What Is An Animal?

What Is An Animal?

What Is An Animal?

• Multicellular• Heterotrophic• Eukaryotic• No cell walls – held

together with structural proteins, mainly collagen

Body Plans

• Animal phyla are categorized based on features that are either present or absent.

• Features often included:– Symmetry– Tissue layers– Body cavities– Protostomes vs. deuterostomes

Body Symmetry

• Asymmetrical• Radial• Bilateral– Dorsal & ventral– Anterior & posterior

Body Tissues

Body Tissues

• No true tissues (no gastrulation)• Diploblastic– Ectoderm & endoderm

• Triploblastic– Also has mesoderm

Body Cavities

• Acoelomate

• Pseudocoelomate

• Coelomate

Protostomes vs. Deuterostomes

Protostomes vs. Deuterostomes

Animal phylogenetic tree

• Zoologists currently recognize about 35 animal phyla

• The current debate in animal systematics– Has led to the development of two phylogenetic

hypotheses, but others exist as well

• One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

Animal phylogenetic tree

Porif

era

Cnid

aria

Cten

opho

ra

Phor

onid

a

Ecto

proc

ta

Brac

hiop

oda

Echi

node

rmat

a

Chor

data

Plat

yhel

min

thes

Mol

lusc

a

Anne

lida

Arth

ropo

da

Rotif

era

Nem

erte

a

Nem

atod

a

“Radiata” Deuterostomia Protostomia

Bilateria

Eumetazoa

Metazoa

Ancestral colonialflagellate

Animal phylogenetic tree• One hypothesis of animal phylogeny based

mainly on molecular data

Calc

area

Silic

area

Cten

opho

ra

Cnid

aria

Echi

node

rmat

a

Chor

data

Brac

hiop

oda

Phor

onid

a

Ecto

proc

ta

Plat

yhel

min

thes

Nem

erte

a

Mol

lusc

a

Anne

lida

Rotif

era

Nem

atod

a

Arth

ropo

da

“Radiata”

“Porifera” Deuterostomia Lophotrochozoa Ecdysozoa

Bilateria

Eumetazoa

Metazoa

Ancestral colonialflagellate

Points of Agreement

• All animals share a common ancestor• Sponges are basal animals• Eumetazoa is a clade of animals with true

tissues• Most animal phyla belong to the clade Bilateria• Vertebrates and some other phyla belong to the

clade Deuterostomia

Disagreement over the Bilaterians

• The morphology-based tree– Divides the bilaterians into two clades:

deuterostomes and protostomes• In contrast, several recent molecular studies– Generally assign two sister taxa to the protostomes

rather than one: the ecdysozoans and the lophotrochozoans