Chapter 27: Introduction to Animal Diversity

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Multicellular

complex bodies

Animal Kingdom (Animalia)

• Multicellular → complex bodies

• No cell walls

• Heterotrophs → ingest food

• Most move actively

• Have specialized tissues (muscle, nerve, etc.)

• Huge diversity in size and form

• Mostly s3xual reproduction

• Have fixed body plans (set during development)

Heterotrophs

ingest food

specialized tissues

muscle, nerve, etc.

Mostly ___ reproduction

s3xual

Epithelial

covers/protects/secretes

Connective

support (bone, blood, cartilage)

Muscle

movement

Nervous

 control/communication

Reproduction & Development

Most animals = diploid (2n)

• Gametes (n) → sperm + egg → zygote (2n)

Asexual Exceptions

• Budding/fragmentation (ex: hydra)

• Parthenogenesis → unfertilized egg develops

• Haplodiploidy (common in insects)

Cleavage

rapid cell division

Blastula

hollow ball of cells

Gastrulation

• → forms:

  • Blastopore (opening)

  • Archenteron (primitive gut)

Early Development Stages

• Cleavage → rapid cell division

• Blastula → hollow ball of cells

• Gastrulation → forms:

  • Blastopore (opening)

  • Archenteron (primitive gut)

Germ Layers (form body tissues)

• Ectoderm → skin + nervous system

• Endoderm → digestive organs

• Mesoderm → muscles, bones, organs

Hox (Homeotic) Genes

• “Master control genes” → control body plan

• Determine:

  • Body segments

  • Limb placement

  • Organization

• Highly conserved (similar across animals)

Symmetry

• Asymmetrical → no symmetry (sponges)

• Radial → around central axis (jellyfish)

• Bilateral → left/right halves → allows cephalization (head)

Tissue Organization

• Parazoa → no true tissues (sponges)

• Eumetazoa → true tissues (all others)

Germ Layers

• Diploblastic → 2 layers (radial animals)

• Triploblastic → 3 layers (most animals)

Functions of Body Cavitys

• Cushions organs

• Allows movement

• Space for organ growth

Acoelomate

 no cavity (flatworms)

Pseudocoelomate

partial cavity (roundworms)

Coelomate

true cavity (most animals)

Protostomes ("first mouth")

• Blastopore → mouth

• Spiral cleavage

• Determinate (cells fixed early)

Deuterostomes ("second mouth")

• Blastopore → anus

• Radial cleavage

• Indeterminate (flexible cells → twins possible)

Animal Phylogeny (Evolutionary Relationships).. Old vs Modern

• Old: based on appearance (morphology)

• New: uses DNA, RNA, molecular data

Major Groups

• Parazoa → sponges

• Eumetazoa → true animals

Eumetazoa split into:

• Radiata → radial symmetry (cnidarians, ctenophores)

• Bilateria → bilateral symmetry (most animals)

Protostomes

• Lophotrochozoa (mollusks, annelids)

• Ecdysozoa (arthropods, nematodes → molt)

Deuterostomes

• Echinoderms (starfish)

• Chordates (humans)

Molecular Discoveries (Modern Changes)

• DNA shows new relationships

• Arthropods now grouped with nematodes

• Some species moved between groups

• Ctenophores may be very early animals

Origins of Animals

• Likely evolved from choanoflagellate-like ancestors

• Early animals were:

  • Simple

  • Soft-bodied

  • Marine

Cambrian Explosion (~541 million years ago)

• Rapid increase in animal diversity

• Most major groups appeared

• Development of:

  • Hard parts (shells)

  • Complex body plans

Still Unanswered : Cambrian Explosion

• Why did it happen so fast?

• Environmental vs genetic causes?

Mass Extinctions

• Many species wiped out suddenly

• Reset ecosystems

• Allowed new species to evolve

What makes animal tissues unique?

→ Lack cell walls and have specialized tissues

What is the difference between diploid and haploid cells?

→ Diploid (2n) = body cells; Haploid (n) = gametes

What is a blastula?

→ Hollow ball of cells

What happens during gastrulation?

Cells move inward → form germ layers and primitive gut

What is cephalization?

→ Concentration of sense organs in the head

What is a coelom?

→ Fluid-filled body cavity

Cleavage in protostomes vs deuterostomes?

→ Protostomes: spiral, determinate
→ Deuterostomes: radial, indeterminate

Which group can form identical twins and why?

→Deuterostomes → indeterminate cleavage