7/1/19

1

Origin of Animals •  Cambrian radiation •  Animal body plans

–  Symmetry –  Tissue systems –  Development

•  Porifera (Sponges) •  Cnidaria (Jellies)

–  True tissues –  Radial symmetry

•  Protostomes –  Lophotrochozoa

•  Molluscs •  Annelids •  Plus other groups we’ll skip

–  Ecdysozoa (tomorrow) July 1, 2019

Brief History of Life

Eukaryotes Diplomonads

Parabasalids

Euglenozoans

Stramenopiles

Alveolates

Rhizarians

algae G

reen

Am

oebozoans Opisthokonts

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates SAR

Apicomplexans

Ciliates

Radiolarians

Forams

Cercozoans

Red algae

Chlorophytes

Charophytes

Plants

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Choanoflagellates

Animals

Unikonta

Archaeplastida

Ch 31

Ch 32-34

Unikonts è

General characteristics of animals:

– Multicellular

– Heterotrophic

– Internal digestion

– Motile

But there are exceptions to each of these�.

The Burgess Shale fossil bed Hallucinigenia

Distinct Body Plans Evolved among the Animals

Look at: – Symmetry – Body cavity (coelom) structure – Segmentation – External appendages

7/1/19

2

Radial symmetry

Bilateral symmetry

Symmetry

Most animals have a central body cavity (Coelom)

Coelom Body covering (from ectoderm)

Digestive tract (from endoderm)

Tissue layer lining coelom and suspending internal organs (from mesoderm)

(a) Coelomate

Body covering (from ectoderm)

Pseudocoelom

Digestive tract (from endoderm)

Muscle layer (from mesoderm)

(b) Pseudocoelomate

Body covering (from ectoderm) Tissue-

filled region (from mesoderm)

Wall of digestive cavity (from endoderm)

(c) Acoelomate

Three tissue layers: •  Endoderm •  Mesoderm •  Ectoderm

Fig. 32-9

Protostome Deuterostome

Eight-cell stage Eight-cell stage

Spiral and determinate Radial and indeterminate Coelom

Archenteron

(a) Cleavage

(b) Coelom formation

Coelom

Key Ectoderm Mesoderm Endoderm

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

Segmentation

Animals Porifera Metazoa

ANCESTRAL PROTIST

Ctenophora Eumetazoa

Deuterostom

ia

Bilateria

Lophotrochozoa Ecdysozoa

Cnidaria

Acoela

Hemichordata

Echinodermata

Chordata

Platyhelminthes

Syndermata

Ectoprocta

Brachiopoda

Mollusca

Annelida

Nematoda

Arthropoda

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

Ediacaran Cambrian PROTEROZOIC PALEOZOIC

Time (millions of years ago) 635 605 575 545 515 485 0

We will concentrate on these seven phyla

Where are humans in this

tree?

7/1/19

3

Is this your ancestor?

•  Colonial Choanoflagellates are the sister group to all other animals

These are protists Not fully multicellular organisms

OTHER EUKARYOTES

Choanoflagellates

Sponges

Other animals

Anim

als

Individual choanoflagellate

Collar cell (choanocyte)

Simple Animal Phylogeny

Sponges Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia

Eum

etazoa Sponges

Link to video

For each major group, think about:

• A familiar example • What is the general body plan?

–  i.e. What kind of symmetry? Does it have a Head? Tissue layers? Body cavity? Legs?

• How does it eat? • How does it move? • How does it reproduce?

Sponge Life cycle

7/1/19

4

Animal Phylogeny Figure 33.UN02

Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia

Eum

etazoa

Diversity among Cnidarians Cnidarians have two body types

Mouth/anus

Gastrovascular cavity

Mouth/anus

Medusa Polyp

Body stalk

Two tissue layers

Simple nerve net

A typical Cnidaria Life Cycle Medusa

Polyp

Animal Phylogeny

7/1/19

5

Protostomes

•  Bilaterally symmetrical •  Anterior brain that surrounds entrance

to digestive tract •  Ventral nervous system with paired or

fused longitudinal nerve cords

Figure 33.UN03

Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia

Bilateria

Mollusca Annelida

A flatworm

Gastrovascular cavity

Mouth

Eyespots Ventral nerve cords

Ganglia

Lophophore

Trochophore

Figure 33.17

(a) A land snail

(b) A sea slug (nudibranch)

Basic body plan of a mollusk Nephridium

Visceral mass Heart

Coelom

Mantle Mantle cavity

Anus

Gill

Gonads

Heart

Intestine

Stomach Shell

Radula

Mouth Esophagus Nerve

cords Foot

Digestive tract

Mouth

Radula

Video

7/1/19

6

Figure 33.20

Mantle Hinge area

Digestive gland

Mouth

Shell

Palp Foot

Mantle cavity Gonad Gill

Incurrent siphon

Water flow

Excurrent siphon

Anus

Adductor muscle (one or two)

Gut Coelom

Heart

Annelida Epidermis Cuticle

Chaetae

Intestine

Fused nerve cords

Clitellum

Crop

Metanephridium

Coelom

Anus

Skin

Intestine

Gizzard

Ventral nerve cords with segmental ganglia Circulatory

system vessels Mouth

Cerebral ganglia

Giant Australian earthworm

Earthworm reproduction

Link to video