1

Overview of Animal Diversity

Chapter 31

2

General Features of Animals

• Heterotrophs• Multicellular• Able to move from place to place• Diverse in form and habitat• Sexual reproduction• Characteristic embryonic development

3

Diverse Kingdom

• Traditional classification of animals– multicellular animals, metazoans,

traditionally divided into 35 distinct phyla First branch - tissues

Parazoa lack definite symmetry and do not possess tissues or organs.

Eumetazoa have definite shape and symmetry and usually have organs and organ systems.

4

5

Traditional Classification of Animals

• Second branch - symmetry– Eumetazoan branch has two principles

branches. Radiata - radial symmetry Bilateria - bilateral symmetry

– Further branches were assigned by comparing key shared features of the body plan.

body cavitycoelom

6

Broad Groupings of Kingdom Animalia

7

Key Transitions in Body Plan

• Evolution of tissues– first key transition in animal body plan

• Evolution of bilateral symmetry– radial symmetry - regular arrangement of

parts around central axis– bilateral symmetry - right and left halves

form mirror images dorsal vs. ventral anterior vs. posterior

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Radial and Bilateral Symmetry

9

Bilateral Symmetry

• Bilaterally symmetrical eumetazoans produce three germ layers.

– ectoderm– endoderm– mesoderm

• Much of the nervous system is in the form of major longitudinal nerve cords.

– ultimately led to evolution of definite head cephalization

10

Three Body Plans

11

Key Transitions in Body Plan

• Evolution of a body cavity– Presence of a body cavity allows digestive

tract to be larger and longer. storage of undigested food more complete digestion more space for gonads to expand

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Key Transitions in Body Plan

• Kinds of body cavities– acoelomates - no body cavity– pseudocoelomates - possess pseudocoel– coelomates - possess coelom

13

Coelomates

• Coelom poses circulation problem– solved by circulatory system

open circulatory systemBlood passes from vessels into

sinuses, mixes with body fluid, and reenters vessels in another location.

closed circulatory systemBlood is physically separated from

other body fluids and can be separately controlled.

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Key Transitions in Body Plan

– Advantages of a coelom Allows contact between mesoderm and

endoderm, so that primary induction can occur during development.

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Key Transitions in Body Plan

• Evolution of deuterostome development– mitotic egg division leads to blastula

indents to form blastopore, opening to the archenteron

• Bilaterians can be divided into protostomes (mouth-first) and deuterstomes (mouth-second).

16

Protostome and Deuterostome Differences

• Cleavage– spiral– radial

• Fate of embryonic cells– determinate - predetermined fate– indeterminate - identical daughter cells

• Fate of blastopore– mouth or anus develops near blastopore

• Formation of coelom

17

Embryonic Development

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Key Transitions in Body Plan

• Evolution of segmentation– advantages

Each segment may go on to develop a more or less complete set of adult organs.

Locomotion is far more effective when individual segments can move independently due to flexibility of movement.

19

Animal Classification is Being Reevaluated

• New look at metazoan family tree– New taxonomical comparisons using

molecular data have come to new, different conclusions.

hint that key morphological characters used in traditional classification are not necessarily conservative

– Molecular systematics uses unique sequences within certain genes to identify clusters of related groups.

20

Roots of the Animal Family Tree

• Origins of metazoans– Most taxonomists agree the animal

kingdom is monophyletic. Three prominent hypotheses exist for

origin from single-celled protists.multinucleate hypothesiscolonial flagellate hypothesispolyphyletic origin hypothesis

– debate over cause of Cambrian explosion