Download Mollusca

Phylum
Mollusca
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Includes these classes:
Snails-class Gastropoda
Clams-class Bivalvia
Octopuses, Squids-class Cephalopoda
• There are more species of mollusks in the ocean than
any other group
• Soft body protected by a shell of calcium carbonate
• Very diverse in body structures and habits
Mollusk Diversity
Biology
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Much more complex than Cnidarians or Sponges
Has a separate mouth and anus (1 way)
Has salivary and digestive glands
herbivores & carnivores (predators & filter feeders)
circulatory system transports nutrients and oxygen
Heart pumps blood to all tissues
Most have open circulatory system (leaky),
cephalopods a closed circulatory system
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Nervous system simple to complex
Most have separate sexes
Some species are hermaphrodites
External fertilization- bivalves, chitons, & some snails
– Sperm & eggs are released into water
• Internal fertilization-cephalopods & most snails
– Cephalopods have modified arm to transfer sperm
to female
class Gastropoda
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Snails-”stomach foot”
Largest group
Approx 90,000 species
Mostly marine
Body is coiled up inside shell
Shell sits on a ventral foot
Nudibranch
(sea slugno shell)
Tulip snail
(with shell)
Body Structure
Mantle
• thin layer of tissue that produces the shell
Foot
Head
• muscular, used in locomotion
• some are well developed & have eyes
• area with small teeth used in scraping algae
or other food from surfaces, made of chitin
Radula
• hard plate used to close opening once
head/foot retracts into shell
Operculum • Gas exchange is through gills
class Bivalvia
• Oysters (cement themselves to
hard surface)
• Clams (burrow)
• Mussels (attach to rocks using
byssal threads),
• Body compressed between
two shells
• Very large source of food for
humans and other marine
animals.
class Cephalopoda-2 in to 30 ft
• Cephalopods-most complex brain of all
invertebrates
– considered intelligent and capable of
learning
• Most cephalopods display color changes
correlated to certain behaviors
• Hectocotylus-Specialized arm transfers a
spermatophore (packet of sperm)
• After eggs hatch female usually dies
Blue-ringed
Octopus
(Hapalochlaena)
giant pacific
octopus - Octopus
dofleini
Giant Squid