Mollusks Mollusks

Zebra MusselsZebra Mussels

Invaded Great Lakes-Invaded Great Lakes-came from Great Britaincame from Great BritainReproduce quickly-one Reproduce quickly-one female releases 40,000 female releases 40,000 Cause problems-clog Cause problems-clog intake pipes-intake pipes-Competition for other Competition for other organismsorganismsClean water since filter Clean water since filter feedersfeeders

Characteristics Characteristics

1.1. Have a head/foot - elongated with an Have a head/foot - elongated with an anterior head-contains mouth and anterior head-contains mouth and sensory system-foot used for locomotion sensory system-foot used for locomotion and attachmentand attachment

2.2. Visceral Mass - contains the organs Visceral Mass - contains the organs

3.3. Have a Mantle – outer covering and Have a Mantle – outer covering and enfolds most of the bodyenfolds most of the body

Cont…Cont…

Coelome - fluid filled body cavityCoelome - fluid filled body cavity

Primary inductionPrimary induction one of the three one of the three primary tissues interacts with another primary tissues interacts with another (endo, meso, ecto)(endo, meso, ecto)

Cont…Cont…

No segmentationNo segmentation

Bilateral symmetryBilateral symmetry

Organs systems for circulation, respiration, Organs systems for circulation, respiration, digestion, and excretiondigestion, and excretion

Trochophore (stationary) or Veliger (free Trochophore (stationary) or Veliger (free swimming found in gastropods and bivalves) swimming found in gastropods and bivalves) larvaelarvae

Veliger

Trochophore

INFOINFO

Respiration - most mollusks breath with Respiration - most mollusks breath with gills (ctenidium) located in their mantle gills (ctenidium) located in their mantle cavity (space between mantle and visceral cavity (space between mantle and visceral mass)-mass)-– visceral mass contain the organsvisceral mass contain the organs– Mantle - heavy fold of tissue wrapped around Mantle - heavy fold of tissue wrapped around

the visceral massthe visceral mass

Sexuality – Diecious, hermaprhoditicSexuality – Diecious, hermaprhoditic– Pulmonate snail – “cupets arrow”Pulmonate snail – “cupets arrow”

Circulation - three chambered heart and Circulation - three chambered heart and Most have open circulatory system-(blood Most have open circulatory system-(blood leaks out of vessels and bathes the body’s leaks out of vessels and bathes the body’s tissues directly, i.e. no capillaries, blood tissues directly, i.e. no capillaries, blood vessels connected to sinuses) vessels connected to sinuses)

Closed circulatory system - octopus and Closed circulatory system - octopus and squid-blood never leaves vessels squid-blood never leaves vessels (capillary system).(capillary system).

ExcretionExcretion nephridia (cilia that beat) rid nephridia (cilia that beat) rid the mollusk of waste-the mollusk of waste-

Mantle secrets a calcareous shell that Mantle secrets a calcareous shell that protects the visceral massprotects the visceral mass– In bivalves this process helps in the In bivalves this process helps in the

production of pearls.production of pearls.

HistoryHistory

Cambrian timeCambrian time 570 MYA 570 MYA

Brachiopods, cephalopods, and Brachiopods, cephalopods, and gastropodsgastropods

Cephalopods in shellCephalopods in shell

Three Major ClassesThree Major Classes

BivalvesBivalves

GastropodsGastropods

Cephalopods Cephalopods

Bivalves Bivalves

sessile (stationary) filter feeders.sessile (stationary) filter feeders.

Two part hinged shell with a hinge keeping Two part hinged shell with a hinge keeping it togetherit together

No distinct head regionNo distinct head region

Siphons-used to filter sea water for foodSiphons-used to filter sea water for food

Reproduce sexually-male, female, Reproduce sexually-male, female, hermaphrodite-external fertilizationhermaphrodite-external fertilization

22ndnd stage of larvae is called veliger stage of larvae is called veliger

Bivalve cont…Bivalve cont…

Oysters, scallop, clam, mussel Oysters, scallop, clam, mussel

Oldest part of shell and bump is called umboOldest part of shell and bump is called umbo

Adductor muscles hold shell together (also Adductor muscles hold shell together (also called a ligament)called a ligament)

If a grain of sand or parasite become lodged If a grain of sand or parasite become lodged between shell and mantle then the mantle between shell and mantle then the mantle secrets a layer of material around the particle secrets a layer of material around the particle forming a pearlforming a pearl

Umbo

GastropodsGastropods

Snails and slugsSnails and slugs

Marine, freshwater, terrestrialMarine, freshwater, terrestrial

Head, foot, visceral mass, and mantleHead, foot, visceral mass, and mantle

Foot used for locomotionFoot used for locomotion

Tentacles on head where eyes are locatedTentacles on head where eyes are located

Single shellSingle shell

Gastropods cont…Gastropods cont…

Respiration either by gills, skin, or lungs Respiration either by gills, skin, or lungs

RadulaRadula rasping tongue that scraps food rasping tongue that scraps food

Undergo torsion or twisting of the shell Undergo torsion or twisting of the shell 180°180°

External & internal fertilizationExternal & internal fertilization

Have Trochophore and veliger (free Have Trochophore and veliger (free swimming) larvaeswimming) larvae

CephalopodsCephalopods

Means head and footMeans head and foot

Foot has evolved into Foot has evolved into tentaclestentacles

Octopus, squid, Octopus, squid, nautilus, cuttlefishnautilus, cuttlefish

Use siphons for jet Use siphons for jet propulsionpropulsion

Cephalopods Cont…Cephalopods Cont…

Have beak for eatingHave beak for eatingClosed circulatory Closed circulatory systemsystemLarge brain and eye-Large brain and eye-can learncan learnHave pigment cells Have pigment cells (chromatophores) in (chromatophores) in epidermis to epidermis to camouflagecamouflage

Cephalopod Shell Hardness Speed Intelligence Color Change AbilityNautilus 1 (external) 3 3 4Cuttle 2 (internal) 2 2 1Squid 3 (internal) 1 4 3

Octopus 4 (none) 4 1 2

Nautilus Cuttlefish

Interesting Interesting ClassClassPolyplacophoraPolyplacophora

ChitonChiton reduced head and flattened foot reduced head and flattened foot

Shell is divided into 8 partsShell is divided into 8 parts

Feed on algaeFeed on algae

External fertilization but no veliger stageExternal fertilization but no veliger stage

HomeworkHomework

Why would you expect the blood pressure Why would you expect the blood pressure inside most mollusk’s blood vessels to be inside most mollusk’s blood vessels to be quite low?quite low?Contrast the feeding habits of Contrast the feeding habits of cephalopods with those of gastropods.cephalopods with those of gastropods.Squids are the fastest swimmers of all Squids are the fastest swimmers of all aquatic invertebrates. Name two aquatic invertebrates. Name two structural adaptations in squids that may structural adaptations in squids that may have enhanced their swimming ability.have enhanced their swimming ability.