Phylum Mollusca (Chapter 27.4) Please set up your notebook for Cornell Notes
Feb 24, 2016
Phylum Mollusca (Chapter 27.4)Please set up your notebook for Cornell Notes
MollusksCharacteristics
Soft-bodied w/ external or internal shellHave a free swimming larval stage called trochophore
Also appear in annelids
Form and functionBody plan
Bilaterally symmetricalFour parts
Foot flat structure for crawling, shovel-shaped for burrowing or tentacles for capturing preyMantle thin layer of tissue that covers the bodyShell made by glands in the mantle that secrete calcium carbonate
Reduced or lost in some groupsVisceral mass internal organs
FeedingHerbivores, carnivores, filter feeders, detritivores or parasitesSnails and slugs have a raspy, tongue shaped structure known as a radula
Can scrape algae off rocks, drill thru shells and tear tissues
Octopi and some sea slugs use sharp jaws to eatSome octopi use poison to subdue prey
Clams, oysters and scallops are filter feedersSiphon a tube-like structure that brings water in and out of the body
RespirationAquatic mollusks use gills inside the mantle cavityTerrestrial mollusks use a large mantle cavity lined with blood vessels
Lining must be moistCirculation
Some mollusks have an open circulatory system (ie. Snails and clams)Other mollusks have a closed circulatory system (ie. Octopi and squid)
ExcretionNephridia remove ammonia from the blood and release it outside of the body
ResponseSimple nervous system small ganglia, few nerve cords and eyespots
Clams, oystersComplex nervous system well developed brains and can remember things for long periods
Octopi, squid, cuttlefish
MovementSnails secrete mucus along base of foot then use rippling motionOctopi use jet propulsion by drawing water into mantle and expelling from siphon
ReproductionSexual
External fertilization release large number of eggs and sperm into water
Snails and two shelled mollusksInternal fertilization
Tentacled mollusks and some snailsSome mollusks are hermaphrodites but fertilize other organisms eggs
Classes of mollusksClass Gastropoda shell-less or single shelled, move by using foot on ventral surface
Snails, slugs, nudibranches (sea slugs)Nudibranches recycle nematocysts from cnidarians to use for protectionSnails withdraw into shell for protection
Class Bivalvia two shelled mollusksClams, oysters, mussels, scallopsTend to stay in one placeFilter feeders
Class Cephalopoda soft-bodied, head attached to a foot that is divided into tentacles
Octopi, cuttlefish, squid, nautilusSmall internal shell or no shell
The only cephalopod with shell is a nautilusLarge eyes