Download squid dissection!!!

Phylum
Mollusca
27-4 Mollusks
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Phylum Mollusca
One of the oldest and most diverse phyla
Second largest phyla of animals
Soft-bodied animals with an internal or
external shell
• Have a free swimming larval stage
Body Plan
• True coelomates
• Complex, interrelated organ systems function
together
• 4 parts: foot, mantle, shell, visceral mass
• Foot: used for crawling, burrowing, tentacles
• Mantle: thin layer of tissue that covers most of
the body
• Shell: made by glands in mantle that secrete
calcium carbonate (reduced or lost in some)
• Visceral Mass- beneath mantle, consists of
internal organs
Feeding
• Herbivores, carnivores, detritovores, parasites
• Radula- flexible, tongue-shaped, rough structure
– Used to scrape algae or eat soft tissues
• Filter feeders- clams, oysters, scallops- siphon water
– Siphon- tubelike structure for water to enter and exit
Respiration, Circulation, Excretion
• Gills in the mantle cavity- snails, clams and octopi
• Through mantle blood vessels- land snails and slugs
• Open circulatory system- snails, clam- slow because
low oxygen demand
• Closed circulatory system- octopi, squid- transports
blood quickly
• Cells release waste into blood and nephridia
remove ammonia from the cell
Response and Movement
• Bivalves- burrow- simple nervous system
– Chemical receptors, eye spots
• Octopi- most highly developed nervous
system in all invertebrates
– Good memory, complex behavior
• Snails move using mucus secreted along the
base of the foot
• Octopi and squid move using jet propulsion
Reproduction
• Sexually
• External fertilization: sea snails and bivalves
• Internal fertilization
– Tentacled and some snails
• Some are hermaphrodites - nudibranchs
– Not self fertilizing
Class Gastropoda
• Pond snails, land slugs, sea
hares, limpets and nudibranch
• “Stomach-foot”
• Single-shelled- protected by withdrawing and
covering the opening with an operculum
– Snails
• No external shell- protected by hiding, ink
squirting, poison, bright colors, nematocysts
– Slugs, nudibranchs, and sea hares
Nudibranch
Class Bivalvia
• Have two shells that are held together by one
or two powerful muscles
– Clams, mussels, oysters, scallops
• Stay in one place, dig or burrow or attach
• Scallops flap shells when threatened
• Cilia or gills create current to circulate water
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Class Cephalopoda
Octopi, squid, cuttlefish, chambered nautilus
“Head-foot”
Most active of the mollusks
Soft-bodied head attached to foot (tentacles)
Tentacles have sucking disks and grab hold of
prey
• Most have an internal shell- except nautilus
• Complex eyes- can distinguish shapes by sight
and texture by touch
Squid-color changes
http://www.youtube.com/watch?v=PrnUIg302mw