Transcript Mollusk & Segmented Worms

Chapter 27
Mollusk & Segmented
Worms
Mollusk: Phylum Mollusca
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Consist of slugs,
snails & animals that
once lived in shells on
the beach
Range from slowmoving slugs to jet
propelled octopus
Mollusk Characteristics
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Most live in the ocean, on
land & freshwater
Some have shells
All are bilateral symmetry
with coelom & 2 body
openings
Have a muscular foot for
movement
Have a mantle
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A mantle is a thin
membrane that
surrounds the internal
organs.
In shelled mollusk,
the mantle secretes
the shell
Mollusk live in a wide variety of
habitats
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Ocean:
oysters,
mussels live
attached to
the ocean
floor
Mollusk live in a wide variety of
habitats
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Ocean:
octopus swim
freely
Mollusk live in a wide variety of
habitats
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Land Dwelling: slugs
& snails can be found
in moist tropical &
temperate climates
Classes of Mollusk
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1.
2.
3.
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There are 7 classes of mollusk.
The 3 that include the most common are
Gastropoda
Bivalvia
Cephalopoda
They look different on the outside, but they
are similar on the inside
Bodies are composed of a foot, mantle, shell &
visceral mass that contains organs
Gastropod-One shelled mollusk
“Stomach Footed Mollusk”
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Land snails, slugs &
marine limpet (sea
slug)
Name comes from
the way the foot is
positioned under the
rest of its body
Many are
hermaphrodites
Marine Limpet
Sea Slug
Land Snail
Land Slug
Body Structure
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Radula-a tongue-like
organ with rows of teeth
used to scrape, grate or
cut food
Simple nervous system
w/ small brain
Blood is pumped by the
heart
Open circulatory system
Radula
Cross-Section of a Snail
Mantle
Shell
Gut
Head
Visceral mass
Shell
Mantle
Foot
Foot
Shelled Gastropods
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Snails, abalones, &
conchs
May be plant eaters,
predators or parasites
Abalones
Conchs
Gastropods without Shells
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Sea Slugs, & Slugs
Sea Slugs feed on
jellyfish & use its
nematocysts to repel
predators
Some secret strong
unpleasant smelling
mucus
They are bright in
color
Bivalves-2 Shelled Mollusk
“Muscle Footed Mollusk”
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Oysters, Clams & Sea
Scallops that have a 2
hinged shell
They strain their food
from the water
Do not have a
distinctive head or
radula
Strong hinge allows the
shell to open and close
Bivalves use cilia to beat & draw
in water over the gills pushing
food particles to the stomach
Cephalopods-Head footed
mollusk
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Predatory squid,
octopus & the
chambered nautilus
Have sharp eyesight,
muscular tentacles,
jet propulsion,
complex brain &
ability to learn
Closed circulatory
system
Octopus & Squid
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Often apply their
intelligence to
capturing prey or
avoiding harmful
situations
Instead of muscular
foot, have tentacles
w/ suckers for moving
& capturing food
Octopus in a coconut shell
Octopus
The Octopus
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Octopus have separate
sexes
Make adapted to
transfer sperm into the
females body
Fertilization is internal,
eggs laid outside the
body
Use “ink” it confuse
predators
Squid
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Squids are known as
"the ice cream cone
of the sea" because
they are a favorite
food of many ocean
dwellers
Backbone & ink sack
used to write with
Cross-Section of a Squid
Arm
Head
Tentacle
Visceral mass
Mantle
Mantle
Shell
Foot
Gut
Chambered Nautilus
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Only shelled member
of the cephalopod
family
Segmented Worms:
Phylum Annelida
Segmented Worms
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Include Bristle worms,
Earthworms, and
Leeches
Term annelid means
“tiny rings”
Bilateral & coleom
with 2 body openings
Characteristic of Annelids
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All Annelids Are made
of segments
Bodies appear to be
divided into rings
Segmentations
continue internally
Each ring is its own
muscle-helps shorten
& lengthens
Parts of the Earthworm
Setae
Intestine Gizzard
Brain
Nerve
Crop
Aortic arches
Parts of the Earthworm
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Mouth: takes in soil, beginning of the digestive
tract
Crop: holds soil before it is passed to the gizzard
Gizzard: grinds food into small pieces so it can
be absorbed.
Setae: helps earthworm move by providing a
way to anchor their bodies in the soil
Circulatory system: closed
Nervous system: nerve fibers connected by
ventral nerve cord to a simple brain
Nephridia: excretory structure
Where do they live?
Everywhere except in frozen soils
of polar regions & dry sand like
soils of the desert
Bristleworms:
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Mostly marine
organisms
Have distinctive head
with eyes & tentacles
Each body segment
has a pair of
appendages called
parapodia which are
bristle like structures
Earthworms
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Are nocturnal animal
Come to surface but
stay close to their
burrows
Cool moist soil
provides protection
during the day
Water in the soil is a
source of oxygen that
soaks into the body
through the skin
Earthworms are hermaphrodites
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2 worms exchange
sperm
Each worm forms a
capsule for the egg &
sperm
The eggs are fertilized
in each worms
capsule & slipped off
into the soil
2-3 weeks young
emerge
Leeches
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Segmented worms
with flatten bodies &
no bristles
Found in different
habitats mostly fresh
water
Have front & rear
suckers
Parasites that suck
blood
OUCH!!!
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The bite is not painful
b/c the saliva contains
a chemical that acts
as an anesthetic
Keeps blood from
clotting & increase
blood flow
Can ingest 2-5 times
its own weight in one
meal
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Once fed-it may not
eat again for a year
WOW!