Kingdom Animalia

What are animals?

• Animals eat to live: ‘ingestively’ heterotrophic

• Multicellular

• lack a cell wall

Origins and Early Diversification of Animals

• Sponges are the oldest known animals in the fossil record and are similar to protistan choanoflagellates.

Water current

Food particles

Choanoflagellate (a protist)

Sponge feeding cell

Water current into sponge

Interior of sponge

Water current out of sponge

Sponge (an animal)

Choanoflagellate cell

Origins and Early Diversification of Animals

• There are about 35 Phyla in Kingdom Animalia

• We’ll review approximately 14 of these

• Four basic features vary in different animal body plans, and are the basis for grouping animals into different phyla:

1. Embryonic tissues

2. Body symmetry

3. Presence of a body cavity

4. Details of early development

1. Tissues

• Tissue= highly organized and functionally integrated group of cells

• All animals but sponges have tissues arranged in layers in their embryos

No tissues

Tissues present

Parazoa(Phylum Porifera)

Eumetazoa(all other phyla)

1. Tissues

• In animals with embryonic tissues, the tissues are arranged in layers

• Endodermdigestive tract, liver, lungs

• Mesodermcirculatory system, muscles

• Ectodermskin, nervous tissue

• There may be 2 or 3 layers:

• Diploblastic endo & ecto only

• Triploblastic all 3

2. Symmetry• An animal’s body plan may have no symmetry (sponges),

or show radial or bilateral symmetry

Multiple planes of symmetry

Radial symmetryAsymmetry

Po

ste

rio

r

Ventral

Dorsal

Single plane of symmetry

An

teri

orBilateral

symmetry

(1. And 2.) Tissues and Symmetry• Animals that are diploblastic show radial symmetry

• Animals that are triplobastic show bilateral symmetry

No tissues

Tissues present

Parazoa(Phylum Porifera)

Eumetazoa

Diploblastic, radial symmetry

Triploblastic, bilateral symmetry

Radiata(Phylum Cnidaria & Ctenophora)

BilateriaAll other Phyla

Significance of Tissues and Symmetry

• Animals with bilateral symmetry are capable of unidirectional movement

• Mesoderm made musculature possible

• Together: directed movement and hunting

3. Fluid-filled body cavities

• A coelom (body cavity) develops within mesoderm tissue in most triploblasts.

• The coelom provides space in which organs can develop and acts as a hydrostatic skeleton in soft-bodied animals.

• Some triploblasts have a pseudocoelom, which develops between mesoderm and endoderm and functions just as a coelom does.

Body plans of the bilateria

Gut

Muscle

Fluid-filled pseudocoelom

Body wall

Hydrostatic skeleton of a nematode

When the muscles on one side contract, the fluid-filled chamber does not compress. Instead, the animal bends.

Muscles contracted

Muscles relaxed

Muscles contracted

Muscles relaxed

Coordinated muscle contractions result in locomotion

3. Bilateria animals either have no coelom, pseudocoelom, or a true coelom

Phylum Platyhelminthes

Bilateria

No coelom

PseudocoelomPhylum Rotifera

Coelomates: All other PhylaCoelom

Phylum Nematoda

4. Early events in embryogenesis

• The last feature used to categorize animal body plans deals with details of the early development of animals

• Animals develop from a single-celled zygote through a process called gastrulation

Figure 32.1 Early embryonic development (Layer 1)

Figure 32.1 Early embryonic development (Layer 2)

Figure 32.1 Early embryonic development (Layer 3)

Early events in embryogenesis

• Among coelomates, there are 2 groups:

• Protostomes: spiral cleavage, mouth develops first, coelom develops within blocks of mesoderm.

• Deuterostomes: radial cleavage, mouth develops second, coelom develops from mesoderm cells that bud off the endoderm.

Figure 32.7 A comparison of early development in protostomes and deuterostomes

Odd group out

• Three phyla of Coelomates have charateristics of both protostomes and deuterstomes

• These are the Lophphorate Phyla

Bilateria

ProtostomiaPhylum MolluscaPhylum AnnelidaPhylum Arthropoda

Bilaterialophophore

LophophoratePhylum BryozoaPhylum PhoronidsPhylum Brachiopoda

Radial cleaveage, mouth second, etc.

Spiral cleavage, mouth first, etc.

DeuterostomiaPhylum EchinodermataPhylum Chordata

Molecular Systematics is moving some branches around on the phylogenetic tree of animals

• Data based on nucleotide sequence of the small subunit ribosomal RNA (SSU-rRNA)

• Early branches still the same

• Deuterostomes still the same

Animal phylogeny based on sequencing of SSU-rRNA

Molecular Systematics is moving some branches around on the phylogenetic tree of animals

• Differences:

• Protostomes divided into 2 groups

• Lophotrochozoaannelids,molluscs, lophophorates

• Ecdysozoanematodes, arthropods

Trochophore larvae of annelids and molluscs

The Ecdysozoa are defined by molting

Nematodes and arthropods shed their

exoskeleton as they grow, a process

called ecdysis

Animal phylogeny based on sequencing of SSU-rRNA