Invertebrates
Animal Characteristics
• Animals are the most physically diverse
kingdom of organisms.
• They range in size from twice the
length of a school bus to microscopic
4 Major Characteristics of Animals
• 1. They are multi-cellular heterotrophs
• 2. Animal cells are supported by collagen
– three-stranded
protein
– found in bone,
skin, ligaments,
fingernails,
and hair
• 3. Animals are diploid and reproduce sexually
Diploid cells have two copies of each chromosome:
one copy from the mother and one from the father
• 4. Animals have Hox genes
– Homeotic genes control early development.
– Hox genes determine the position of cells
differentiation.
– A Hox gene mutation leads to the development of
a body structure in the wrong position and/or
animal diversity
Animal Diversity
• Animals are grouped into vertebrates (animal
with backbones) or invertebrates (animals
without backbones)
• More than 95% of all animal species are
invertebrates- an animal without a backbone
Animals are grouped according to
these 3 criteria
• 1. Body Plan
• 2. Tissue Layers
• 3. Developmental Patterns
gastrovascular
cavity
mouth
mesoglea
brain
muscle
hearts
blood vessels
mouth
segment
digestive track
nerve cord
oral arms
tentacles
There are two types of Body Plans
Bilateral Symmetry
Body divides equally along one
plane
Radial Symmetry
• Body arranged in a circle
around a central axis
Tissue Layers
Bilateral
• Have 3 distinct layers:
ectoderm, endoderm, and
mesoderm
– Ecto- develops into skin,
the brain, and nervous
system
– Endo- lines the “gut”
– Meso- develops into
internal organs
Radial
• Have two distinct layers:
ectoderm and endoderm
Animals are separated into two major
groups
• Protostome- mouth
develops before anus
• Deuterostome- anus
develops before mouth
Invertebrate Diversity
Sponges
• Sponges are the most
primitive animals on
Earth.
• Sponges share common
characteristics.
– Sessile- attached to floor
of ocean (do not move)
– reproduce both sexually
and asexually
– filter feeders- strain food
particles from water
Sponges have
three types of cells
1. Pinacocytes- form
the sponges outer
layer
2. Choanocytes- pull
water into sponge
and help trap food
3. Ameobocytesabsorb and digest
food particles
spicule
pore
osculum
pinacocyte
amoebocyte
choanocyte
Sponge Video
Cnidarians (Jellyfish)
• Cnidarians come in two body forms
– Polyp- cylindrical tubes with mouth and tentacles
facing upward
– Medusa- umbrella-shaped, with mouth and
tentacles on the underside
Cnidarian Video
Cnidarian Anatomy
• Cnidarians are made up of two tissue layers
separated by mesoglea
• The outer tissue layer has three cell types.
– contracting cells – covers the surface of the
cnidarian
– nerve cells- sends information around animal
to coordinate movement
– cnidocytes (which contain nematocysts)“stinging cells” used for defense and capturing
discharged
of prey
nematocyst
barbs
coiled
nematocyst
Flatworms
• Flatworms have a solid body and incomplete
or absent gut.
• They have no circulatory system
head
pharynx
mouth
sucker
gut cavity
eyespot
reproductive
system
3 classes of Flatworms
• Planarians- free-living non parasites
• Flukes – parasites which can infect humans and
cause serious disease (schistosomiasis)
– Infects 200 million people in Africa and Southeast Asia
– Contracted by wading in or drinking contaminated
water
• Tapeworms- are parasites that live in vertebrates gut
– Use suckers or hooks to attach to host
– Absorb nutrients from the food the host eats
Tapeworm Video
Mollusks
• Mollusks have a complete digestive tract with
two openings – a mouth and an anus
• Coelom ( fluid filled body cavity)is present
– Except in flatworms
• Mollusks have all three tissue layers
• Have a brain and spinal cord (cephalization)
• Have a circulatory system
– Primitive species (open) such as bivalves
– Advanced species (closed) such as octopus and squid
Mollusks Anatomy
• Mollusks share at least one of three features.
– radula : file like teeth used to obtain food
– mantle : area of tissue covering the internal
organs, sometime secrete a hard outer
shell for protection
– ctenidia: flat gills found in the mantle
intestine
heart
mantle cavity
mantle
stomach
digestive gland
foot
radula
salivary gland
anus
crop
mouth
• Most mollusks are classified into three classes.
– Gastropods: includes snails, abalone, and slugs
they are found on both land and water
– Bivalves (Pelecypods): clams, oysters, mussels,
and scallops. Protected by two hinged
shells
– Cephalopods: squid, octopus, nautiluses, and
cuttlefish. Most advanced mollusks and
are predators
Mollusk Video #1
Mollusk Video
• http://my.hrw.com/content/hmof/science/hig
h_school_sci/tx/gr912/hmd_bio_9780544073890_/dlo/biologyvid
eoclips/index.html?vid=92
Annelids
• Three groups of Annelids
– earthworms, leeches, and marine worms
• They are characterized by having
segmentation: division of the organism into
repeated sections
• They have a coelom and all three tissue layers
• They breathe by diffusing oxygen through
their skin
• They are hermaphroditic so they can
reproduce either sexually or asexually
Annelid Video
• http://my.hrw.com/content/hmof/science/hig
h_school_sci/tx/gr912/hmd_bio_9780544073890_/dlo/biologyvid
eoclips/index.html?vid=91
Roundworms
• Roundworms have bilateral symmetry and
shed their outer skeleton to grow.
• Roundworms are protostomes with
bilateral symmetry
pharynx
intestine
brain
cuticle
anus
tail
• Roundworms have a psuedocoelom (“false”
not complete body cavity)
• They do not have a respiratory or circulatory
system