Download Part 8 - glenbrook s hs

Body Cavities a fluid-filled space separating the digestive tract from the outer
body wall. (body cavity = coelom or gut)
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Functions:
Its fluid cushions the suspended organs to
prevent internal injury
It enables internal organs to grow and move
independently of the outer body wall; makes
exercise not harmful to internal organs
In soft-bodied animals (earthworms) it functions
as a hydrostatic skeleton against which muscles
can work. (ex: for burrowing)
Ex: Flatworms lack a body cavity = Acoelomate
Ex: Roundworms have a body cavity partially
lined by mesoderm (middle layer of tissue) =
Pseudocoelomate
Ex: Earthworms have a body cavity completely
lined by mesoderm = Coelomate
Details of embryonic development:
• Of the animals with a true
coelom, there are 2 branches :
• Branch 1: mollusks, annelids,
arthropods: mouth develops first
in embryo = Protostomes.
• Branch 2: echinoderms and
chordates: anus develops first in
embryo = Deuterostomes.
Animalia Kingdom 8 Major Invertebrate Phyla:
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Porifera
Cnidaria
Platyhelminthes
Nematoda
Mollusca
Annelida
Arthropoda
Echinodermata
Invertebrates, animals without backbones,
represent more than 95% of the animal
kingdom!
Sea Anemone: Which Phylum?
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1. Phylum Porifera - Sponges
• Sponges are sessile.
• Sponges are the simplest animals,
probably evolved very early from
colonial protists
• Range in height from about 1 cm
to 2 meters.
• Have no nerves or muscles, and
consist of about 9,000 species.
• About 100 species lives in fresh
water and the rest are marine.
• The body of a sponge resembles a
sac perforated with holes.
Sponges Feeding Method:
• Most sponges feed by
collecting bacteria from the
water which streams through
their porous bodies(filter
feeding).
• Flagellated cells called
choanocytes trap bacteria in
mucus and then engulf the
food by phagocytosis.
• Cells called amoebocytes pick
up food from the choanocytes,
digest it, and carry nutrients to
other cells.