An Introduction to Animal Diversity

Page
4

Spiral and determinate

Radial and indeterminate

Coelom

Archenteron

(a) Cleavage

(b) Coelom formation

Coelom

Key

Ectoderm

Mesoderm

Endoderm

Mesoderm

Mesoderm

Blastopore

Blastopore

Solid masses of mesoderm

split and form coelom.

Folds of archenteron

form coelom.

Anus

Mouth

Digestive tube

Mouth

Anus

Mouth develops from blastopore.

Anus develops from blastopore.

(c) Fate of the blastopore

Slide 23

New views of animal phylogeny are emerging from molecular data

Zoologists recognize about three dozen animal phyla.

Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well.

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

Another hypothesis is based mainly on molecular data.

Slide 24

A view of animal phylogeny based mainly on morphological and developmental comparisons

ANCESTRAL

COLONIAL

FLAGELLATE

Metazoa

Eumetazoa

“Porifera”

Bilateria

Deuterostomia

Protostomia

Cnidaria

Ctenophora

Ectoprocta

Brachiopoda

Echinodermata

Chordata

Platyhelminthes

Rotifera

Mollusca

Annelida

Arthropoda

Nematoda

Slide 25

A view of animal phylogeny based mainly on molecular data

Silicea

ANCESTRAL

COLONIAL

FLAGELLATE

Metazoa

Eumetazoa

“Porifera”

Bilateria

Deuterostomia

Lophotrochozoa

Ecdysozoa

Calcarea

Ctenophora

Cnidaria

Acoela

Echinodermata

Chordata

Platyhelminthes

Rotifera

Ectoprocta

Brachiopoda

Mollusca

Annelida

Nematoda

Arthropoda

Slide 26

Points of Agreement

All animals share a common ancestor.

Sponges are basal animals.

Eumetazoa is a clade of animals - eumetazoans with true tissues.

Most animal phyla belong to the clade Bilateria, and are called bilaterians.

Chordates and some other phyla belong to the clade Deuterostomia.

Slide 27

Progress in Resolving Bilaterian Relationships

The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes.

In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa.

Ecdysozoans shed their exoskeletons through a process called ecdysis.

Slide 28