Transcript What is a Mollusk?

Unit 8
Chapter 27
Mollusks and
Segmented Worms
What is a Mollusk?
Bilateraly symmetry,
coelomates, and
well-developed
body systems
Soft bodies covered
by a thin mantle,
which may secrete
a shell
What is a Mollusk?
Mollusks have a foot,
a ventral structure
for locomotion
Some have an open circulatory system,
blood moves through vessels & into open
spaces around body organs
Others have a closed circulatory
system, blood moves through the body
enclosed entirely in blood vessels
What is a Mollusk?
Gastropods
include snails and
slugs
One shell, “bellyfooted”
Radula = scraping
tongue-like
structure
Radula magnified 1000X
What is a Mollusk?
Bivalves include clams, oysters & muscles
Two shells,
“hatchet-footed”
Filter-feeders
What is a Mollusk?
Cephalopods include octopus, squid,
cuttlefish, & chambered nautilus
Little or no shell,
foot divided into
tentacles with suckers
Use ink and jet propulsion
to escape from danger
What is a segmented worm?
Phylum Annelida
Bilaterally symmetrical, segmented
coelomates, with two body openings
What is a segmented worm?
Earthworms have complex body systems:
Digestive system includes a crop & gizzard
for grinding food taken from soil
Closed circulatory system includes 5 pair of
“hearts”
Reproductive system includes both ovaries &
testes
What is a segmented worm?
Leeches are
freshwater,
external parasites
Some microsurgeons
use leeches after
surgery to improve
blood flow
What is a segmented worm?
Marine worms include bristle worms, fan
worms and tube worms (below)
Most have structures for swimming or
crawling on the bottom of the sea