Phylum MolluscaPhylum Mollusca

the “mollusks”the “mollusks”

General CharacteristicsGeneral Characteristics

– Have a soft body sometimes enclosed in a shell Have a soft body sometimes enclosed in a shell – Have a ventrally located muscular foot used for Have a ventrally located muscular foot used for

movementmovement– The larvae stage is called a trochophore – The larvae stage is called a trochophore –

microscopic and free swimming often not microscopic and free swimming often not resembling the adultresembling the adult

– Considered coelomates – meaning they have a Considered coelomates – meaning they have a fluid filled body cavity (coelom)fluid filled body cavity (coelom)

– Have a specialized organ called a radula which Have a specialized organ called a radula which is used to scrape food off of hard surfacesis used to scrape food off of hard surfaces

Feeding and DigestionFeeding and Digestion

•Members of this phylum are filter feeders, Members of this phylum are filter feeders, herbivores or active carnivoresherbivores or active carnivores

•All members have a one way gut with two All members have a one way gut with two openingsopenings

•Bivalves are filter feeders using the siphon to Bivalves are filter feeders using the siphon to gather water to filtergather water to filter

•Gastropods tend to gather algae using their radulaGastropods tend to gather algae using their radula

•Cephalopods are carnivores that capture their Cephalopods are carnivores that capture their prey using their arms and tentacles and then prey using their arms and tentacles and then chew up the prey using a hard beak found chew up the prey using a hard beak found between the armsbetween the arms

ExcretionExcretion

• Have a complex Have a complex excretion system excretion system that gathers waste in that gathers waste in a nephridia (similar a nephridia (similar to our kidneys)to our kidneys)

• This system recovers This system recovers water and nutrients water and nutrients and expels a and expels a concentrated waste concentrated waste productproduct

Circulation and RespirationCirculation and Respiration

• Complex circulatory Complex circulatory system that moves system that moves nutrients through nutrients through the bodythe body

• Most members have Most members have a three chambered a three chambered heartheart

• Marine mollusks Marine mollusks have gills located in have gills located in the mantle cavitythe mantle cavity

ReproductionReproduction

•Most members have distinct male and Most members have distinct male and female sexual membersfemale sexual members

•Some have the ability to change sexes Some have the ability to change sexes between male and femalebetween male and female

– This helps keep the population high by providing This helps keep the population high by providing the right ratio of male to femalethe right ratio of male to female

Class GastropodaClass Gastropoda

• Include snails, slugs, nudibranches and Include snails, slugs, nudibranches and abalonesabalones

•Range in size from microscopic to 1 meterRange in size from microscopic to 1 meter

•Most have a single shell but some have lost Most have a single shell but some have lost this shell completely like the slug and this shell completely like the slug and nudibranchnudibranch

•Most have tentacles on top of their head Most have tentacles on top of their head that contain simple eyesthat contain simple eyes

•Often a source of food for humansOften a source of food for humans

•Most are herbivoresMost are herbivores

Class BivalvesClass Bivalves

•Examples are clams, mussels and oystersExamples are clams, mussels and oysters

•The body is laterally compressed with two The body is laterally compressed with two shells that are hinged at the bottomshells that are hinged at the bottom

•Gills are used not only for respiration but Gills are used not only for respiration but also to filter debris out of the water for also to filter debris out of the water for feedingfeeding

•Strong muscles are used to open and close Strong muscles are used to open and close the shellthe shell

•Have sense organs on the edge of the Have sense organs on the edge of the mantle that respond to light and touchmantle that respond to light and touch

Class Bivalves cont.Class Bivalves cont.

•Some have siphons which are used to bring Some have siphons which are used to bring oxygen to the bivalve that is buried in the oxygen to the bivalve that is buried in the sand; allows buried organisms to filter feedsand; allows buried organisms to filter feed

•They have byssal threads which they use to They have byssal threads which they use to attach themselves to hard surfacesattach themselves to hard surfaces

•Pearls are produced by oysters or clams – Pearls are produced by oysters or clams – the pearl is basically the same material that the pearl is basically the same material that the shell is made of:the shell is made of:

– It forms around a piece of sand, debris or It forms around a piece of sand, debris or irritation that has gotten into the body cavity and irritation that has gotten into the body cavity and is irritating the clamis irritating the clam

Class CephalopodsClass Cephalopods

• Characterized as strong predators that specialized in Characterized as strong predators that specialized in movementmovement

• Group includes octopus, squids, cuttlefish and nautilius.Group includes octopus, squids, cuttlefish and nautilius.

• Most are active swimmers that have a vestigial shell Most are active swimmers that have a vestigial shell present, but reduced in size and not used by the animalpresent, but reduced in size and not used by the animal

• Movement is achieved by bringing water into the funnel Movement is achieved by bringing water into the funnel and pushed out the siphonand pushed out the siphon

– The funnel is a muscular part of the foot found under the The funnel is a muscular part of the foot found under the headhead

– The siphon is another tube that is flexible and moveable The siphon is another tube that is flexible and moveable to help steer the squidto help steer the squid

• Foot is modified into tentacle with sucker discs to Foot is modified into tentacle with sucker discs to capture preycapture prey

Class CephalopodaClass Cephalopoda

•Octopuses have eight arms and range in size Octopuses have eight arms and range in size between 2 inches and 30 feetbetween 2 inches and 30 feet

•Squid have eight arms and two long tentacles Squid have eight arms and two long tentacles and range in size between a few inches to more and range in size between a few inches to more than 65 feetthan 65 feet

• All members of this class squirt ink if disturbed All members of this class squirt ink if disturbed – this acts as a smoke screen to hide them from – this acts as a smoke screen to hide them from predatorspredators

•the members of this class have a well defined the members of this class have a well defined brain and are capable of complex behaviors as brain and are capable of complex behaviors as seen in the movie “incredible suckers”seen in the movie “incredible suckers”