5. molluscs. phylum mollusca 200,000 species200,000 species –more species in ocean than any other...

5. Molluscs5. Molluscs

Phylum Mollusca Phylum Mollusca

• 200,000 species200,000 species

– More species in ocean than any other animal groupMore species in ocean than any other animal group

• Soft body enclosed by calcium carbonate shellSoft body enclosed by calcium carbonate shell

• Body covered by Body covered by mantlemantle

– Thin layer of tissue that secretes the shellThin layer of tissue that secretes the shell


• Displays Bilateral SymmetryDisplays Bilateral Symmetry

• Ventral muscular foot used for Ventral muscular foot used for locomotionlocomotion

• Most had have that includes eyes Most had have that includes eyes and other sensory organsand other sensory organs

Essentially, a mollusc is a coiled Essentially, a mollusc is a coiled mass of vital organs wrapped mass of vital organs wrapped in a dorsal shell.in a dorsal shell.


• Some have Some have radularadula– Ribbon of small teeth used to rasp food from Ribbon of small teeth used to rasp food from

surfacessurfaces– Made of chitinMade of chitin

What’s a radula and how does it work? What’s a radula and how does it work? Modern woodworkers could tell you! Modern woodworkers could tell you!

micrograph of a mollusc radula: note themicrograph of a mollusc radula: note thechisel-like designchisel-like design


• Have paired gillsHave paired gills

• Portion of body may be coiled and asymetricalPortion of body may be coiled and asymetrical

• Occupy all marine environments – rocky shores to Occupy all marine environments – rocky shores to hydrothermal ventshydrothermal vents

Essentially, a mollusc is a coiled Essentially, a mollusc is a coiled mass of vital organs wrapped mass of vital organs wrapped in a dorsal shell.in a dorsal shell.

•Gastropods (Class Gastropoda), or stomach foot,Gastropods (Class Gastropoda), or stomach foot, are the most common mollusks.are the most common mollusks.

•Snails, limpets, abalone, and nudibranchs.Snails, limpets, abalone, and nudibranchs.

•75,000 spp.75,000 spp.

nudibranch, nudibranch, Phidiana crassicornisPhidiana crassicornisCooper’s nutmeg snailCooper’s nutmeg snailCancellaria cooperiCancellaria cooperi

giant keyhole limpetgiant keyhole limpetMegathrua crenulataMegathrua crenulata

red abalone red abalone Haliotis rufescensHaliotis rufescens

Cone snail, Cone snail, Conus geographusConus geographus

Class Gastropod – Stomach Footed Class Gastropod – Stomach Footed

• Coiled mass of vital organs enclosed by a dorsal Coiled mass of vital organs enclosed by a dorsal shell resting on a footshell resting on a foot


• Most use radula to scrape algaeMost use radula to scrape algae

• Mud snails are deposit feedersMud snails are deposit feeders

• Whelks, oyster drills, and cone shells are carnivores that Whelks, oyster drills, and cone shells are carnivores that prey on clams, oysters, worms, and small fishes prey on clams, oysters, worms, and small fishes – Modified Radula to drill and rasp preyModified Radula to drill and rasp prey


• Nudibranchs (sea slugs)Nudibranchs (sea slugs)– No shellNo shell

– Colorful branches of the gut and gillsColorful branches of the gut and gills

– Prey on sponges and other invertebratesPrey on sponges and other invertebrates

– Produce noxious chemicals or retain undischarged nematocysts Produce noxious chemicals or retain undischarged nematocysts taken undigested from preytaken undigested from prey

Bivavles: Class BivalviaBivavles: Class Bivalvia

Class BivalviaClass Bivalvia

• Clams, mussels, and oystersClams, mussels, and oysters

• Body laterally compressed and enclosed with two parts Body laterally compressed and enclosed with two parts (valves)(valves)

• No head or radulaNo head or radula

• Gills expanded and folded used to obtain oxygen, and filter Gills expanded and folded used to obtain oxygen, and filter and sort food particles from waterand sort food particles from water

Scallops also filter feed. Many have striking color patters.Scallops also filter feed. Many have striking color patters.


• Inner surface of shell lined w/ mantle so whole Inner surface of shell lined w/ mantle so whole body lies in mantle cavitybody lies in mantle cavity

• Strong muscles used to close valvesStrong muscles used to close valves


• Clams burrow in sand or mud and water drawn in Clams burrow in sand or mud and water drawn in and out of mantle by and out of mantle by siphonssiphons– Allow clam to feed and obtain oxygen while buriedAllow clam to feed and obtain oxygen while buried


• Mussels secrete Mussels secrete byssal threads byssal threads that attach them to that attach them to rocks and other surfacesrocks and other surfaces


• Oysters cement their left shell to hard Oysters cement their left shell to hard surface and other to another oystersurface and other to another oyster– Pearls occur when irritating particles are Pearls occur when irritating particles are

lodged within the mantle cavity and lodged within the mantle cavity and covered by secretions (CaCOcovered by secretions (CaCO33) from ) from

oysteroyster


• Some scallops can swim by rapidly ejecting water Some scallops can swim by rapidly ejecting water from mantle cavity with from mantle cavity with siphonsiphon


• Shipworm bores in mangroves, driftwood, and Shipworm bores in mangroves, driftwood, and pilingspilings– Have symbiotic relationship w/ bacteria in the gut that Have symbiotic relationship w/ bacteria in the gut that

digests wooddigests wood

– Valves lie at the inner end of tunnel lined w/ calcium Valves lie at the inner end of tunnel lined w/ calcium carbonate and siphon protrudes from entrancecarbonate and siphon protrudes from entrance

– Fouling organism Fouling organism = settles on bottoms of boats, pilings, = settles on bottoms of boats, pilings, and other submerged surfacesand other submerged surfaces

CephalopodsCephalopods““Putting Your Head and Feet Together”Putting Your Head and Feet Together”

Class Cephalopoda (head footed)Class Cephalopoda (head footed)

• Predators specialized in locomotionPredators specialized in locomotion

• Octopi, squid, and cuttlefishOctopi, squid, and cuttlefish

• Agile swimmers w/ complex nervous system and reduction Agile swimmers w/ complex nervous system and reduction or loss of shellor loss of shell

• All are marineAll are marine

Cephalopod (General Morphology)Cephalopod (General Morphology)

While still following the basic body plan of a mollusc, octopi While still following the basic body plan of a mollusc, octopi are highly specialized. are highly specialized.

Cephalopod (General Morphology)Cephalopod (General Morphology)

• Large eyes on side of headLarge eyes on side of head

• Thick muscular mantle which protects headThick muscular mantle which protects head

• Water enters mantel and leaves through Water enters mantel and leaves through siphonsiphon = jet propulsion = jet propulsion

Cephalopod: OctopiCephalopod: Octopi

• OctopiOctopi– Eight long arms (2 in to 30 feet)Eight long arms (2 in to 30 feet)

– Bottom dwellers that live in crevices, bottles, etcBottom dwellers that live in crevices, bottles, etc

– Have beak-like jaws and radula to rasp flesh and secrete Have beak-like jaws and radula to rasp flesh and secrete paralyzing substanceparalyzing substance

– Distract predators with dark fluid from ink sacDistract predators with dark fluid from ink sac

Cephalopod: SquidCephalopod: Squid

• SquidSquid– Two triangular fins on mantle – better swimmers than Two triangular fins on mantle – better swimmers than

octopioctopi

– Can remain motionless, move forward, or backwardCan remain motionless, move forward, or backward

– Eight arms and two tentacles, all with suckersEight arms and two tentacles, all with suckers

– Has pen in upper surface of mantleHas pen in upper surface of mantle

– Few cm to 60 feet!!Few cm to 60 feet!!

Cephalopod: CuttlefishCephalopod: Cuttlefish

• Cuttlefish Cuttlefish – Eight arms and two tentacles, but body flatten w/ fin Eight arms and two tentacles, but body flatten w/ fin

running along the bodyrunning along the body

– Have calcified internal shell aids in buoyancyHave calcified internal shell aids in buoyancy

Cephalopod: Chambered NautilusCephalopod: Chambered Nautilus

• Chambered NautilusChambered Nautilus– Coiled external shell containing gas filled chambers Coiled external shell containing gas filled chambers

serves as buoyancy organserves as buoyancy organ

– Has suckerless tentaclesHas suckerless tentacles

Other MolluscsOther Molluscs

• Chitons (class Polyplacophora – bearer of many plates)Chitons (class Polyplacophora – bearer of many plates)– All marineAll marine

– Eight overlapping shell plates covering dorsal surfaceEight overlapping shell plates covering dorsal surface

– Live in shallow hard bottomsLive in shallow hard bottoms

– Have radula to rasp algaeHave radula to rasp algae

Other Molluscs Other Molluscs

• Tusk shells or scaphopods (class Scaphopoda)Tusk shells or scaphopods (class Scaphopoda)– Elongated shell tapered at end resembling elephant tuskElongated shell tapered at end resembling elephant tusk

– Sandy muddy bottoms in deep waterSandy muddy bottoms in deep water

– Many species have thin tentacles to capture small preyMany species have thin tentacles to capture small prey

Tusk shell Tusk shell hermit crabhermit crab

Biology of Molluscs: Nervous SystemBiology of Molluscs: Nervous System

• Gastropods and bivalves have Gastropods and bivalves have ganglia ganglia (local (local brains) located in different parts of bodybrains) located in different parts of body


• CephalopodsCephalopods– Most complex of invertebratesMost complex of invertebrates

– Brains coordinate and store informationBrains coordinate and store information

– Complex eye reflects developmentComplex eye reflects development

– Octopi and cuttlefish can learnOctopi and cuttlefish can learn


• CephalopodsCephalopods– Display rapid color change coordinated with behaviors Display rapid color change coordinated with behaviors

and moods, from sexual display to camouflage and moods, from sexual display to camouflage

– Cuttlefish “flash lights” while octopi change color and Cuttlefish “flash lights” while octopi change color and behavior to mimic poisonous fish and sea snakes behavior to mimic poisonous fish and sea snakes

http://www.sciencefriday.com/video/http://www.sciencefriday.com/video/08/05/2011/where-s-the-octopus.html08/05/2011/where-s-the-octopus.html

Biology of Molluscs: Reproduction and Biology of Molluscs: Reproduction and Life HistoryLife History

• Most have separate sexes (some hermaphroditic) Most have separate sexes (some hermaphroditic)

• Bivalves, chitons, tusk snails, and some gastropods Bivalves, chitons, tusk snails, and some gastropods release sperm and egg into waterrelease sperm and egg into water

• Cephalopods and most gastropods – internal Cephalopods and most gastropods – internal fertilizationfertilization

Biology of Molluscs: Reproduction and Biology of Molluscs: Reproduction and Life HistoryLife History

• Cephalopods – modified arm to transfer Cephalopods – modified arm to transfer spermatophorespermatophore – Develop in yolk-filled eggs attached to crevicesDevelop in yolk-filled eggs attached to crevices

– Female dies – guarding eggs = no foodFemale dies – guarding eggs = no food

• Some have Some have trochophoretrochophore larvae, displaying larvae, displaying relationship to segmented wormsrelationship to segmented worms

Kings of Camouflage Kings of Camouflage

• http://www.youtube.com/watch?v=In7n590GjxU

http://www.youtube.com/watch?v=In7n590GjxU

5. molluscs. phylum mollusca 200,000 species200,000 species –more species in ocean than any other...

Documents

shell slide

foot slide

class bivalvia slide

water slide

chitin slide

design slide

rasp prey slide

conus geographus slide