Mollusca and Annelida By Daniel Smith, Mackenzie Neighbors and Margaret Gaines

Some Useful Terms Mantle - a single or paired outgrowth of the body wall that lines the inner surface of the valves of the shell in mollusks Trochophore - small, free-swimming, ciliated aquatic larva of mollusks and annelids Setae - stiff bristle-like hair used for movement in earthworms radula - a band in the mouth of most mollusks that is set with numerous, minute teeth and is drawn backward and forward over the floor of the mouth to break up food Crop - a pouch in the foregut of arthropods and annelids for holding food

More Useful Terms Torsion - the rotation of the visceral mass, mantle and shell 180˚ with respect to the head and foot of the gastropod. This brings the mantle cavity and anus to an anterior position above the head Septa - a division of the coelum (a partition between segments of it) in annelida Visceral mass – area which contains most internal organs

General Information Both Mollusks and Annelids have three germ layers Both are also protostomes Mollusks move by using a foot that is extremely muscular Mollusks have one coelum while Annelids have multiple coelums Mollusks reproduce sexually while Annelids reproduce both sexually and asexually Both have Bilateral Symmetry

Classes of Mollusca Cephalopoda including squid, octopuses, nautilus, cuttlefish; all marine Gastropoda including sea snails with shells and marine snails without a shell or with a reduced shell; land snails and slugs, freshwater snails Bivalvia including clams, oysters, scallops, mussels Polyplacophora including chitons that live on rocky marine shorelines Scaphopoda including tusk shells; all marine Aplacophora including solenogasters, and the subclass Caudofoveata which are deep-sea worm-like creatures Monoplacophora deep-sea limpet-like creatures

Cephalopoda Predators that include squid, nautiluses, cuttlefish, and octopuses Have a head surrounded by a foot that is divided into arms and tentacles Nautiluses have strong shells, cuttlefish an internal shell, squid some vestiges of a shell while octopuses don’t have one

Octopus v. Squid No hard shells Short life-span, commit programmed suicide after reproduction Eggs are watched over by mothers until hatched Feed in plankton cloud until mature Crawl with some swimming Eight arms Extremely good sight Thought to be as intelligent as a dog Hard shells Eggs are released into water in cases by most, some tend their eggs and then die Also feed in plankton cloud Mostly swim and use tentacles for hunting Eight arms, two tentacles Can be much larger than octopuses, one has been measured at 59 feet in length

Gastropoda Mostly bottom feeders, some filter feeders Most inhabit relatively large shells that serve as shelter – sea slugs(gastropods) don’t Most marine gastropods wander on rocky parts of the bottom because their foot doesn’t attach to sediments like sand and mud

Bivalvia (bivalves) Filter feeders anchored to the bottom Can live in sedimentary Some bivalves dig with a strong muscular foot and others use their foot to create strong threads that attach them to rocks

Polyplacophora Foot Chiton

Scaphopoda Tusk Shell

Aplacophora The Foot of this animal is contained in the groove above Solenogastres

Monoplacophora Monoplacophora were thought ho be extinct until someone found one in the fifties, as a result we don’t have many pictures of them.

Classes of Annelida Oligochaeta aka earthworms –good at tilling the soil Polychaeta- each segment has a parapodium for locomotion –Parapodium- a pair of paddlelike/ridgelike structures similar to feet –The parapodium contains many setae which are made up of chitin. Hirundinea aka leeches (freshwater and land leeches) –Parasitic and sucks blood of victim. Can suck up to 10 times its weight.

Reproduction (in depth) They are hermaphrodites that can cross- fertilize. –asexually by fragmentation/regeneration –sexually: –1) males exchange sperm and store it. –2) They make a “mucous cocoon” –3) This cocoon attaches to the side of the worm and picks up eggs –4) Once egg and sperm meet the cocoon slides off into the soil to grow

Movement Parapodia (made up of setae) that function as feet to move the annelid along Land: crawl/ burrow Aquatic: drift or swim

Body Development Segmented!!! 1mm to 3m length Coelom separated by septa Complete digestive track Longitudinal blood vessels and nerve cords that penetrate septa

Specialized Tissue Metanephridia- excretory tubes that remove waste from blood and fluid in coelom Digestive system is complex: –Crop –Gizzard –Intestine –Pharynx Ganglia- similar to brain. Has nerve cells connected to pharynx ( where food comes in)

Polychaeta Have two bristles(parapodia) on each segment of their bodies, they are like setae but for aquatic usage instead of terrestrial Sometimes called bristle worms Chaetae Segments

Oligochaeta Earthworms

Hirundinea Leech