Lesson 18 Outline list Lesson 20
Fundamentals of Biology
Lesson 19
Mollusks, Echinoderms
I. Mollusca.
A. General Structure.
1. Bilateral symmetry.
2. The ventral aspect is comprised of
a muscular foot, used for locomotion and gripping rocks.
3. The visceral hump
contains the internal organs: heart, digestive, excretory.
4. The dorsal aspect is covered by a mantle.
a. A
thickened fold of tissue that covers the visceral hump and sometimes overhangs
it.
b. Secretes
the shell.
5. The mantle cavity is
a space between the mantle and the visceral hump.
6. A shell often covers
the mantle.
a.
Protection.
b. Anchors
the muscles.
7. The head contains
the sensory organs, brain, and mouth.
B. Body systems.
1. Digestive.
a. Radula,
mouth, stomach, intestine, anus.
b. The radula,
a small organ like a tongue made of sandpaper, scrapes up food particles and
draws them into the mouth.
2. Circulatory.
a. True
heart.
b. Closed
vessels that pass through the gills or lungs.
c. An open,
blood-filled cavity that bathes the internal tissues.
3. Excretory: nephridia.
4. Respiratory: gills or lungs hang
down in the mantle cavity.
5. Neural.
6. Reproductive: many have a larval
stage.
C. Bivalvia.
1. Oysters, clams, mussels, scallops.
2. Most are marine, some freshwater.
3. Two-part hinged shell (each half
called a valve).
4. Most are ciliary filter feeders.
a. Lack a
radula.
b. Circulate
water through two siphons.
c. Food is
trapped in a stringy, sticky mucus.
d. Cilia move
the food and mucus mixture into the mouth.
5. Most are sedentary.
D. Gastropoda.
1. Snails, slugs, limpets,
nudibranches.
2. Marine, freshwater, terrestrial.
3. Foot located immediately below the
visceral hump, where the stomach is.
4. Locomotion by gliding over a thin
layer of slime.
5. Graze on plant material.
6. Shell (if present) is spiral coil
or flattened cone.
7. Anus empties on top of head.
8. Some have a "lung" in
the mantle cavity.
E. Cephalopoda.
1. Octopuses, squid, nautiluses,
cuttlefish.
2. Shells.
a. Nautiluses
have external shells.
b. Squid have
a rod-like internal cuttlebone made of calcified chitin.
c. Octopuses
have no shell of any sort.
3. Foot extends from the head region.
4. Foot is usually divided into 8 to
10 sucker-bearing tentacles.
5. Carnivorous.
6. Closed circulatory system.
7. Internal fertilization.
8. Octopuses and squid.
a. Large,
complex eyes.
b. Highly
developed brain.
c. Can swim
by jet propulsion.
d. Squid can
reach 60 feet long.
F. Amphineura.
1. Chitons.
2. Marine.
3. Oval, with 8 lateral plates.
4. Shallow water and intertidal
areas.
5. Feed on algae.
6. External fertilization.
II. Echinodermata.
A. General Characteristics.
1. Means "spiny skinned."
2. CaCO3 spines and plates under the
skin.
3. Relatively sedentary.
4. Most begin as ciliated,
bilaterally symmetrical larvae.
5. Radial symmetry in adults.
6. No head or excretory system.
7. The central disk
contains the mouth, stomach, and anus.
8. Water vascular system
with tube feet.
9. All are marine.
10. Separate sexes, external
fertilization.
11. Can regenerate if a portion of
the central disk is present.
B. Water vascular system.
1. A modified portion of the coelom
that acts as a hydraulic device.
2. A ring canal circles the central
disk.
3. Radial canals extend to each arm.
4. Opens to the sea at the sieve
plate on the dorsal side of the central disk.
5. In sea stars, tube feet protrude
from the radial canals along their length.
6. The tube feet have suckers on
their ventral end, and ampullae at the opposite end.
7. The ampullae can contract, forcing
water into the foot and causing it to extend.
8. Coordination of the suckers,
ampullae, and muscles enable locomotion.
9. Can withstand the force of the
surf, and can pry open mollusk shells.
C. Other Systems.
1. Eat by everting their stomach and
secreting digestive enzymes into the prey.
2. The resulting soupy broth is
transported throughout a highly branched digestive glands for digestion to be
completed.
3. Respiration occurs directly
between the coelom and the environment.
4. Skin gills are extensions of the
animal surface that aid in respiration and excretion.
5. Amebocytes move through the coelom
gathering waste, then exit the animal through the skin gills.
D. Asteroidea - sea stars.
1. Flat, with central disk.
2. Most are carnivorous.
3. Eat mollusks.
4. Regenerate whole body from part of
one arm plus central disk.
E. Echinoidea - sea urchins, sand dollars.
1. Brittle calcareous spines.
2. CaCO3 plates fused into solid
sphere or envelope with openings for mouth, anus, feet.
3. Tube feet used for gas exchange.
4. Lack arms.
5. Scavengers.
F. Ophiuroidea - brittle stars, serpent stars.
1. Similar appearance to Asteroidea,
but disk more distinct, arms thinner and tentacle-like.
2. Many are covered with spines.
3. Most eat organic detritus and
small organisms.
4. Readily discard their arms when
attacked or disturbed.
G. Holothuroidea - sea cucumbers.
1. Look like large flabby sausages.
2. Skeleton reduced to microscopic
plates.
3. Lack arms.
4. Lie on side, with mouth at end.
5. Trap organic material on their
sticky, feathery tentacles.
6. Shed their internal organs when
attacked, then regenerate them.
H. Crinoidea - sea lilies, feather stars.
1. Some are sessile.
2. Branched, feathery arms.
3. Ciliated tube feet.
a. Carry food
to mouth.
b. Surface
for gas exchange.