Download PHYLUM MOLLUSCA

PHYLUM MOLLUSCA
• “MALACOLOGY” • not drab and
mundane
as
found
on
• The study of
the N.A. continent
molluscs
• of the eight classes,
only 3 are common
Read 147-156
• 50,000 -100,000
living species
• 35,000 extinct
species
• Largest = 1000 lbs.
• 80% less than 5 cm
Classes of Mollusca
•
•
•
•
Class Bivalvia (Clams, oysters)
Class Gastropoda (snails, slugs)
Class Cephalopoda (Squid, octopus)
Class Polyplacophora (Chitons)
• Additional classes not covered
– Class Scaphopoda
– Class Caudofoveata
– Class Solengastres
– Class Monoplacophora
Unifying characteristics
“INDICATORS OF COMMON ANCESTRY”
• 1. Visceral mass (internal organs) heart,
digestion excretion, reproduction
• 2. Mantle- tissue surrounding the visceral
cavity, secretes shell (which may be present
or absent)
• 3. Muscular foot - organ for propulsion
• 4. Head- mouth, sense organs, cerebral
ganglia
• 5. Trochophore- juvenile larvae form
• 6. Radula
– Ribbon of small teeth that are used to
feed
– Made of chitin
• 7. Siphon
• 8. Gas exchange through gills
• Habitat
– Fresh and salt water and a few
terrestrial
Trochophore Larva
• All the members of
this phylum start
their life as a free
living
“trochophore”
Generalized Mollusk Anatomy
Dorsal mantle covers the
visceral mass.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Radular Structure
Source: From A Life of Invertebrates, Copyright © 1979 W. D. Russell-Hunter.
Radula
http://www.wildsingapore.com/chekja
wa/pixhtoz/i900b1.gif
http://www.personal.dundee.ac.uk/~a
mjones/radula.jpg
CLASSES
Class Polyplacophora
Chitons
Class Polyplacophora
• Eight dorsal plates
• Reduced head
• Radula reinforced with
iron
– Scrape algae from
rocks
• Multiple gills, along
sides of body between
foot and mantle edge
Class Polyplacophora
Mouth
Mantle cavity
Ctenidium
Foot
Anus
Chitons
Class Gastropoda
Snails, Slugs, Conchs, Limpets
Class Gastropoda
•
•
•
•
“STOMACH FOOT”
One shell (if present)
single muscular foot
- operculum- trap
door to close for
protection
• - radula- scraping
tongue
• - can be parasites
-some can have
symbiotic relationship
with algae
"zooxanthellae”
•Torsion of body
Snail
• Terrestrial
• Mantle cavity
functions as lung
Snail
Shell
Pneumostome
Tentacle
(Eye stalks)
Tentacle
Anus
Foot
Mouth
Genital pore
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Internal Structure of a Generalized Gastropod
Helix – garden snail
I’ll get there by
midnight, I think…
Nudibranch
• No shell
• Dorsal projections
– Gills
– Nematocyst discharge
Abalone
• Several holes in top of shell
– Excrete waste
• Food for man
Interesting but don’t write this?
Nudibranchs
• Gastropods that have lost
their shell
• Breathe through their
cerata (colorful branches
on their dorsal side)
• Often produce toxic
chemicals for protection
• Or steal undischarged
nematocysts taken from
their prey.
Slug
• No shell
• Garden pests
Limpet
• Herbivores
• Cling to rocks or other surfaces
Conch
• Large shell
• Marine
• Many are predators
0057.jpg
0060.jpg
0063.jpg
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Class Bivalvia
Clams, Oysters, Shipworms
Class Bivalvia
• Two shells
• No eyes, a few
species with eyes on
• shell has two lateral
mantle margin
valves with dorsal hinge
• foot usually wedge• Most are filter feeders
shaped
• No head or radula
• Body enclosed in mantle • Burrow
– Sand, wood, rocks
• Head greatly reduced
Giant Clam & Burrowing Clam
Siphon
It’s Like a Straw
• Siphon – tube that
sticks out of shell
• Incurrent siphon
takes in water
carrying food and
oxygen
• Excurrent siphon
carries water
containing wastes
and CO2 out
• Gills used to obtain oxygen
and to filter out small food
particles from the water
• Adductor muscles keep
shells closed
• As bivalve grows, it adds a
layer to its shell
Bivalves
Figure 16.31a
Clam Dissection
The Blue Mussel
• Uses byssal threads
to attach to the
substrate
• Threads are secreted
by the mussel’s foot
• Anchors mussel in
place on rocks to
make filter feeding
easier
• Experimented with as
a dental adhesive
Scallops
Shipworms
Class Cephalopoda
Squids, Octopuses, Nautiluses
Giant Squid
“A live giant squid (Architeuthis)
http://news.nationalgeographic.com/news/2005/09/0927_050927_
giant_squid.html
measuring roughly 25 feet long
attacks a baited fishing line off the
Ogasawara Islands. Japanese
scientists recently released the
first-ever images of a live giant squid
in the wild. Many giant squid have
washed up on beaches or have been
found dead or dying in fishing nets.
This specimen was found in New
Zealand in 1996.”
http://news.nationalgeographic.com/ne
ws/2006/12/061222-giant-squid.html
• - Intelligent and have a complex eye
(as in humans) can form images by
moving the lens in and out (How do
we focus?)
• - chromatophore- pigment sacks with
the 3 primary colors. Nerves cause
them to expand and contract. (spots
to dots)
• - octopus crawls and squids swim in
schools (jet propulsion)
• Marine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cephalopod Eye
Class Cephalopoda
•high extinction
10,000 fossils down
to 400 species today
• Shell in squid and
octopus absent or
vestigial
• Ink sac
• Foot modified into
arms and tentacles
• All predators
Ammonoids
• Extinct
• Devonian to
Cretaceous
– 400 to 65 MYA
• Died out with
dinosaurs
Squid
“you will learn this when we do the dissection”
Posterior surface
Right
Ventral
Dorsal
Left
Squid
Tentacle
Arm
Funnel (siphon)
Collar
Eye
Fin
Squid
Shell (Pen)
Systemic
heart
Branchial heart
Ctenidium
Funnel
Squid Male
Testis
Penis
Hectocotylous arm
Squid Female
Ovary with eggs
Oviducal gland
Nidamental glands
Oviducal opening
Octopus
• Eight arms with
suckers
• Most intelligent
invertebrate
Cuttlefish
Who Wants a Snack?
• Catches prey with
tentacles
• Suction disks on
tentacles used to
grasp and hold prey
• Bite from beak kills
prey
– Poisonous venom in
some cases
Squid
0093.jpg
Nautilus
• Up to 94 tentacles
– No suckers
• Shell with many
chambers
– Lives in outermost
chamber
Chambered Nautilus
0089.jpg
But They Don’t Have
Shells! How do they
protect themselves?
• Fast swimmers (jet propulsion)
– Force water out the mantle cavity through the siphon.
The siphon can move and point the animal in any
direction
•
•
•
•
Camouflage: Chromatophores
Ink Cloud
Intelligence
Vision
Economics
• Pearls
• Burrowing shipworms
• Snails & slugs
– Garden pests
– Food
– Intermediate hosts for
parasites
Oysters
Pearl formation
Shell
Developing pearl
Epithelium
Irritant lodged between shell and mantle
Layers of nacre secreted around foreign material
Zebra Mussel
• Environmental Pest
• Ballast water of ships
from Europe in 1986
• Attack be secreting
adhesive byssal
threads
– Each other
– Other mussels
– Man made objects
• Pipes, plumbing
Zebra Mussel
• Live in high densities
• Feed on
phytoplankton
• Reproduce rapidly
Zebra Mussel
• Attach to native
mussels
• Killed all native
mussels in Lake Erie
Distribution of Zebra Mussel