Phylum Mollusca
• 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• 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
• 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
• 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 slug-no shell)
Tulip snail(with shell)
Body Structure• thin layer of tissue that produces the shell
• 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
• hard plate used to close opening once head/foot retracts into shell
• Gas exchange is through gills
MantleMantle
FootFootHeadHead
RadulaRadula
OperculumOperculum
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