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.

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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 cavity  coelom

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

8 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

12 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 system  Blood passes from vessels into sinuses, mixes with body fluid, and reenters vessels in another location.  closed circulatory system  Blood is physically separated from other body fluids and can be separately controlled.

14 Key Transitions in Body Plan – Advantages of a coelom  Allows contact between mesoderm and endoderm, so that primary induction can occur during development.

15 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

18 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 hypothesis  colonial flagellate hypothesis  polyphyletic origin hypothesis – debate over cause of Cambrian explosion