Segmented Worms &
Mollusks
Biology A
Ms. Williams
Segmented Worms
• Phylum Annelida - means “little rings”
• Examples - Earthworms, leeches and
bristleworms
Characteristics of Segmented
Worms
•
•
•
•
•
Bilateral symmetry
Coelomate
2 body openings
“tube within a tube”
Setae - bristles to
help them move
through soil
• Found in moist
environments
Nervous system
• Simple nervous system - nerve cords and
some have a simple brain called a ganglia
Circulatory System
• Closed circulatory system - contains blood
vessels
• These blood vessels are connected by 5
simple “hearts”
• Exchange gases through their skin
• This is why earthworms come out when it
is raining
Digestive System
• See your worm packet for details
Reproduction
• Most are hermaphrodites, so they have to
cross fertilize
• Benefits of annelid
• Earthworms eat through soil; when they
turn the soil it provides space for air to flow
Benefits of annelids
• Earthworms eat
through soil
• When they turn the
soil, it provides space
for air to flow
Benefits of annelids
• Nutrients are passed
out in castings - the
waste of earthworms
• This helps to fertilize
soil
• Can be sold in stores
Mollusks
• Phylum Mollusca - “soft bodied”
• Examples - snails, clams, squid
Characteristics of mollusks
•
•
•
•
•
Some have shells
Bilateral symmetry
Coelomates
2 body openings
Muscular foot for
movement
Characteristics of mollusks
• Mantle - think
membrane that
surrounds the internal
organs. If a mollusk
has a shell, this
secretes it
Reproduction in mollusks
• Most have separate sexes
• However, they have external fertilization
(happens in the water)
• Land gastropods are hermaphrodites
Nervous system
• Simple in that it has
brain and nerves
• Most have paired
eyes
Circulation
• Well developed
circulatory system
with a 3 chambered
heart
• Some have an open
circulatory system body organs exposed
directly to blood
Circulation
• Others have a closed
circulatory system the blood is closed
entirely in vessels
Respiration
• Most have gills
• Land snails & slugs - the mantle is evolved
into a primitive lung
Excretion
• Oldest known animals to evolve excretory
structures called nephridia
• These are used to remove metabolic
wastes
Types of Mollusks
• There are 7 classes of mollusks, but we
will focus on the 3 most common
Gastropods
• Gastropod - “stomach
foot”
• Examples - snails,
slugs, conches,
limpets
Gastropod characteristics
• Have one shell or none
• Can be found in freshwater, salt water or
moist terrestrial habitats
• May be plant eaters, parasites or
predators
• Use a radula to eat with; a tongue like
organ with rows of teeth to scrape food
Snail radula
Bivalves
• Bivalves - “two
shelled”
• Examples - clams,
oysters, mussels and
scallops
Characteristics of bivalves
• Most are marine, others fresh water
• Most use large muscular food for
borrowing
• Filter feeders - use cilia to draw in water
Foot of bivalve
Cilia of bivalve
Cephalopods
• Cephalopod - “head
footed”
• Examples - squid,
octopus, cuttlefish,
nautilus
Characteristics of cephalopods
•
•
•
•
Marine
The only one with a shell is the nautilus
Food evolved into tentacles
Tentacles catch prey and pull it into
beaklike jaws
• Use siphons to “swim through water
• Escape from danger releasing ink into the
water to form a cloud