Diversity of Life
The Eukaryotes III: Animals
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How many animal species are known to us? Why so many?
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Gallery
Characteristics of animals
- Multicellular eukaryotes
- Nutrition: ingestive heterotrophs
- Sexual reproduction (most)
- Complex embryonic development
- Zygote à
Blastula à
Gastrula à
Embryo à
(Larva) à
Adult
- Earliest animals have radial symmetry
- Sponges
- Jellyfish & sea anemones
- Bilateral symmetry results in specialization of head (cephalization)
- Flatworms, roundworms etc.
- Pentaradial symmetry: an exception in the trend
- Earliest animals have no true tissues
- Development of true tissues: endoderm and ectoderm
- Development of middle tissue: mesoderm
- Primitive animals have no cavity
- "False" coelom forms between mesoderm and endoderm
- True coelom forms within mesoderm
Development of digestive tract
- Primitive animals have only a cavity
- Sponges, cnidarians, flatworms
- One-way digestive tract first arose in roundworms
- Protostomates: animals whose digestive tract forms "mouth first"
- Molluscs, annelids, arthropods
- Deuterostomates: animals whose digestive tract forms "mouth
second"
Animal Diversity
- Porifera: The Sponges
- Epidermal cells, feeding cells (choanocytes), transport cells (amoebocytes)
- Spicules (skeleton fibers) for support; may be hard or
soft
- Cnidarians: jellyfish et al.
- Hollow gastrovascular cavity for eating, circulation
- Most have 2 life
stages: polyp and medusa
- Feeding tentacles have stinging cells (cnidocytes)
- Examples: Jellyfish,
coral,
sea anemone
- Platyhelminthes: The Flatworms
- Bilateral, with gastrovascular cavity
- Flat; may be 1 mm - 20 m in length
- Examples: Fluke,
Tapeworm, Planaria
- Nematodes: The Roundworms
- Very diverse: > 90,000 species
- One-way digestive tract, false coelom
- Most are free-living, some are parasitic
- Examples: Pinworm, Trichinella
- Mollusca: Snails etc.
- 150,000 + species known, mostly marine
- Coelom, one-way GI tract, specialized organs
- Soft bodies; hard shell in most
- Bodies have 3 main
parts: foot, visceral mass, mantle
- Open circulatory system in most
- Examples: snails, slugs, clams, oysters, squid,
octopus
- Annelids: Segmented worms
- Segmentation and closed circulation
- Examples: Earthworm, polychaetes, leeches
- Arthropods
- > 1 million species known; most wide-spread and numerous animals
- Body plan
segmented, with jointed appendages
- Exoskeleton (chitin) - requires molting
- Head, thorax, abdomen, 6 - 8 legs, antennae (most)
- Arachnids: spiders, ticks, mites, scorpions
- Crustaceans: crabs, lobster, shrimp, barnacle, pill bugs
- Millipedes and centipedes
- Insects: moth, bee, grasshopper
- adapted to flight: 1 or 2 pairs of wings
- 3 pairs of walking legs
- Metamorphosis in many includes larvae (maggots, grubs,
caterpillars)
- Insects are important as pollinators, pests, in food chains,
as disease vectors
- Echinoderms
- "Spiny-skinned", pentaradial
- Water vascular system for circulation and feeding (tube feet)
- Exampls: sea
stars, sea
cucumbers, sea urchins
- Chordates
- 4
characteristics: pharyngeal gill slits, post-anal tail, notochord,
dorsal nerve cord
- Invertebrates: lancelets and
tunicates
(sea
squirts)
- Vertebrates: fish, birds, mammals, amphibians, reptiles
- Class Agnatha: jawless
fish
- Class Chondrichthyes: cartilagenous
fish
- Class Ostheichthyes: bony
fish
- Ray-finned fish: salmon,
seahorse
- Lobe-finned fish: coelocanth
- Lungfish
- Class Amphibia: toads,
frogs, salamanders
- Class Reptilia: turtles,
snakes,
crocodiles,
alligators,
chameleon, dinosaurs
- Class Aves: owls, eagles, emu
- Class Mammalia: mammals
- Monotremes: platypus
- Marsupials: kangaroo
- Eutherians: mouse