Download Phylum Molluska

Phylum
Mollusca
“softbodied”
•4 Primary Classes
–Class Gastropoda: Snails, conchs,
slugs, sea slugs, sea hares, limpets,
etc. (very diverse)
Gastropoda: “stomach-footed”
Snails and slugs
Class Bivalvia:
Clams, oysters and scallops
Bivalvia: “two halves”
Clams, oysters, scallops, mussels
Class Cephalopoda:
Octopi, squid, nautilis, cuttlefish
Cephalopoda: “head-footed”
Octopi, cuttlefish, squid, nautali
http://www.youtube.com/watch?feature=
player_detailpage&v=YVvn8dpSAt0
Blue-Ring Octopus
Cuttlefish
Squid
Giant Squid
Avg. length:
35 feet
Max.
Length:
80 feet
Colossal Squid
Maximum length:
43 feet
http://www.ted.com/talks/david_gallo_
shows_underwater_astonishments.html
Class Polyplacophora:
Chitons
Body plan
• Bilateral Symmetry
• Muscular foot used for locomotion, burrowing and
capturing prey
• Mantle, an outgrowth of tissue that covers
most of it’s body. This secretes the shell.
• Coelom -Body cavity primarily around heart
• Shell - Made of calcium carbonate, internal or external
• Viceral mass – the internal organs
Feeding
•Complete digestive system
•Herbivores use a radula to scrape algae
from rocks
•Carnivores use jaws to eat prey
like the octopus
•Filter feeders use a siphon to catch plankton
Respiration
•Gas exchange via gills, lungs
•Land snails respire through a
mantle or its body surface
Circulation
• Open circulatory system- except cephalopods,
where the blood is transported through the
body via a cavity called the hemocoel
• Leaving the vessels, blood travels through
sinuses or large sack-like spaces
• Possess blood vessels by a heart
• Fast moving mollusks have a closed circulatory
system using blood vessels
Excretion
• Tube shaped nephridia remove ammonia from
the blood and release it outside the body
Response
• Nervous system varies greatly. Other than
cephalopods, it is very basic. Several ganglia in
clams and bivalves
• Cephalopods have a highly developed brain
and nervous system, near equal to vertebrates.
Movement
• Some secrete mucus
• Others like the octopus move by jet propulsion
Reproduction
• Reproduction is sexual by external fertilization
as in snails and bivalves
• Some are hermaphroditic like the snail
Ancestry of Molluscs
Phylum Significance
• Eaten for food by humans and other animals.
Clams, oysters, scallops, mussels, (shellfish) snails
(escargot), octopus and squid are popular foods
• Research - i.e. snails appear to be cancer free
• Indicators of environmental pollution
• Land snails and slugs damage gardens and crops
• Shipworms destroy wooden boats, docks, and
piers.
• Filter feeders can concentrate toxins through
biological magnification (Humans eating them can
become ill or even die).