The Simplest Animals
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Transcript of The Simplest Animals
The Simplest Animals
Phylum Porifera Invertebrates Animals without tissues (Sponges) All are aquatic and sessile (stay in
one place) The body plan is asymmetrical Made of a loose arrangement of cells
with no defined cell layer
Sponges!
Sponges Have two germ layers, ectoderm and
endoderm They do have some specialized cells
• Collar cells line the inside of the body cavity and have flagella that move water and food into the sponge through pores
• Water exits via the osculum (the open end of the sponge
• Digestion occurs in collar cells, or special cells called amoebocytes
• Amoeobocytes wander around in a gelatinous mixture called mesenchyme
Sponge Reproduction Sponges are hermaphrodites (produce
both male and female gametes) They only produce one gamete at a time
(they can’t fertilize themselves) Fertilized eggs turn into free-swimming
larva The larva undergoes metamorphosis and
develops into a full grown sponge They can also reproduce asexually, by
budding or branching
Role of Sponges Important food
source for snails, sea stars and fish
Provide shelter for smaller invertebrates inside their body cavity
Some clean up the ocean floor by releasing chemicals
Phylum Cnidaria Include Hyrda, Jellyfish, Sea Anemones,
and Corals Aquatic, have tentacles and possess true
tissues Radially symmetrical Have endoderm and ectoderm, separated
by jelly-like mesoglea Have nerve, muscle and digestive tissues Nerve nets encircle the body, so if
touched, they can flatten out and pull tentacles inward
Cnidarians!
Cnidarian Body Structure Either polyp or
medusa form
Cnidarian Feeding Capture food using
stinging cells containing nematocysts (stinging capsules)
Captured food is digested in the gastrovascular cavity (gut) which has only one opening
Cnidarian Reproduction Hydra may reproduce asexually by
budding Hydra and all medusae reproduce
sexually by releasing eggs or sperm into the surrounding water
Role of Cnidarian Food for fish, turtles and small
animals Sea anemones and coral reefs form
protective structures Coral reefs protect land along coastal
areas from rough water