Transcript Foot

2nd Largest animal phylum on Earth
~150,000
known
species
snails, slugs, clams, squids, and
octopi
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Latin mollus: “soft”
• Almost all habitats
• Soft-bodied animals, usually with a hard external shell (Calcium
containing).
• Some have lost the shell completely.
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• Most mollusks are marine, though some
inhabit fresh water, and some snails and
slugs live on land.
• Mollusks are soft-bodied animals, but
most are protected by a hard shell of
calcium carbonate.
– Slugs, squids, and octopuses have reduced
or lost their shells completely during their
evolution.
Protostome coelomates
-3 main body parts: Foot, Mantle, Visceral Mass
the coelom is reduced
and limited to region
around heart
• foot (typically for locomotion), a visceral
mass with most of the internal organs, and a
mantle.
– The mantle, which secretes the shell, drapes
over the visceral mass and creates a water-filled
chamber, the mantle cavity, with the gills, anus,
and excretory pores.
– Many mollusks feed by using a straplike rasping
organ, a radula, to scrape up food.
Body Plan:
Foot:
-Flat: crawling
-Spade-shaped:
burrowing
-Tentacles:
capturing prey
Mantle: thin layer
of tissue that
covers the body.
Visceral mass
- contains internal
organs:
Water
intake
and
output
Feeding:
Can be herbivores,
carnivores, filter
feeders, detritivores,
or parasites.
Respiration:
•Aquatic-Gills through diffusion
• Blue hemocyanin, not hemoglobin, is respiratory
pigment
•Has copper instead of iron
•Land- mantal cavity lined with
blood
vessalsdiffusion
•Must be kept
moist
Circulation:
•Open circulatory system with
blood-filled spaces called hemocoels
•a heart pumps hemolymph through
vessels into a hemocoel
Excretion:
• nephridia
Movement:
• Mucus
• Jet propulsion
• rapid clapping of valves releases
water in spurts
Reproduction:
Sexual-external fertilization (Snails)
- internal fertilization (tentacled)
- hermaphrodites
Four main classes:
1-Polyplacophore
• Chitons are marine animals with oval
shapes and shells divided into eight dorsal
plates.
• Chitons use their muscular foot to grip the
rocky substrate tightly and to creep slowly
over the rock surface.
• Chitons are grazers
that use their radulas
to scrape and ingest
algae.
•Have 2 shells held together by adductor
muscles that close the shell tightly to protect
the animal.
•Feed by filtering small particles from the
water
•sedentary, attached to hard surface
•foot used for digging in sand
• Mantle cavity contains gills -feeding and gas exchange.
• Filter feeders
–Cilia convey the
particles to the
mouth.
–Water flows into
mantle cavity via
the incurrent
siphon, passes over
the gills, and exits
via the excurrent
siphon.
Sexes are separate; the gonad is located around coils of
intestine
• Most bivalves live rather sedentary lives.
– Sessile mussels secrete strong threads that tether
them to rocks, docks, boats, and the shells of other
animals.
– Clams can pull themselves into the sand or mud,
using the muscular foot as an anchor.
– Scallops can swim in short bursts to avoid predators
by flapping their shells and jetting water out their
mantle cavity.
3-Gastropoda: “univalves”: snails and slugs
-Greek gaster: “stomach”
-Single shell in snails
-Can close “door” if threatened
Move by muscular contractions of the single foot
Slugs have either a reduced shell or no shell at all
Use a radula for feeding
3-Gastropoda:
• Most are marine, but there are also many
freshwater or terrestrial species.
• In place of the gills found in most aquatic
gastropods, the lining of the mantle cavity of
terrestrial snails functions as a lung.
respiratory pores
Aquatic gastropod gills are in the mantle cavity
Land snails are hermaphroditic.
a. In pre-mating behavior, they meet and shoot
calcareous darts into each other's body wall.
b. Each inserts a penis into the other's vagina; this
provides sperm for future fertilization.
c. Eggs are deposited in soil and development
proceeds without formation of a larvae.
Hermaphroditism assures that any two animals can
mate-very useful in slow-moving animals
• Some species are predators.
– Radula is modified to bore holes in the shells of
other organisms or to tear apart tough animal
tissues.
– The tropical marine cone snails, teeth on the
radula form separate poison darts, which
penetrate and stun their prey, including fishes.
4- Cephalopoda: “head-foot mollusks”: cuttlefish,
squids and octopuses
Giant squid can reach 4400 lbs.!!
-Very active and can be fast
swimmers
-reduced shell or no shell
-tentacles are modified foot
-move by “jet propulsion”
-Can have large eye
• Cephalopods use rapid movements to dart toward
their prey which they capture with several long
tentacles.
• Squids and octopuses use beaklike jaws to bite their
prey and then inject poison to immobilize the victim.
• A mantle covers the
visceral mass, but the
shell is reduced and
internal in squids,
missing in many
octopuses, and
exists externally
only in nautiluses.
• Squids and octopuses possess ink sacs; they
squirt a cloud of ink to escape predators.
• A squid has three hearts, one pumps blood to
internal organs; two pump blood to gills
• Octopuses and squids move by "jet propulsion",
sucking water into a muscular sac in the mantle
cavity surrounding their bodies and quickly
expelling it out a narrow excurrect siphon.
Cephalopods have an active, predaceous lifestyle
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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