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