gastropods and pelecypods

Gastropods and Gastropods and PelecypodsPelecypods

How to make a living How to make a living inside your shellinside your shell

Phylum MolluscaPhylum Mollusca

Ancient Group of AnimalsAncient Group of Animals Second “largest” animal phylumSecond “largest” animal phylum Over 100,000 extant species Over 100,000 extant species

describeddescribed Marine, freshwater, terrestrial Marine, freshwater, terrestrial

(flying is the only lifestyle mollusks (flying is the only lifestyle mollusks haven’t accomplished)haven’t accomplished)

Diversity of body formsDiversity of body forms


Class GastropodaClass Gastropoda


Class GastropodaClass Gastropoda Class Bilvalvia (Pelecypoda)Class Bilvalvia (Pelecypoda)


Class GastropodaClass Gastropoda Class BivalviaClass Bivalvia Class CephalopodaClass Cephalopoda


Class GastropodaClass Gastropoda Class BivalviaClass Bivalvia Class CephalopodaClass Cephalopoda Class PolyplacophoraClass Polyplacophora


Class GastropodaClass Gastropoda Class BivalviaClass Bivalvia Class CephalopodaClass Cephalopoda Class PolyplacophoraClass Polyplacophora Class MonoplacophoraClass Monoplacophora


Class GastropodaClass Gastropoda Class BivalviaClass Bivalvia Class CephalopodaClass Cephalopoda Class PolyplacophoraClass Polyplacophora Class MonoplacophoraClass Monoplacophora Class ScaphopodaClass Scaphopoda


Class GastropodaClass Gastropoda Class BivalviaClass Bivalvia Class CephalopodaClass Cephalopoda Class PolyplacophoraClass Polyplacophora Class MonoplacophoraClass Monoplacophora Class ScaphopodaClass Scaphopoda Class AplacophoraClass Aplacophora

What makes a mollusc a What makes a mollusc a mollusc?mollusc?

The molluscan “bauplan”The molluscan “bauplan” Body divided into three regionsBody divided into three regions

Head (typically reduced)Head (typically reduced) FootFoot Visceral massVisceral mass



HeadHead FootFoot Visceral massVisceral mass

Body has a unique “organ” the mantleBody has a unique “organ” the mantle Covers the dorsal portion of the animalCovers the dorsal portion of the animal Is folded into a “skirt” to form a chamber that houses Is folded into a “skirt” to form a chamber that houses

the gills, and openings for digestive, urinary, and the gills, and openings for digestive, urinary, and reproductive systemsreproductive systems

May have several functionsMay have several functions Secretes a calcareous shell in some forms (bivalves, Secretes a calcareous shell in some forms (bivalves,

most gastropods, some cephalopods, most gastropods, some cephalopods, monoplacophora, polyplacophra)monoplacophora, polyplacophra)

General Body Structure of General Body Structure of a Molluska Mollusk




Body has a unique “organ” the mantleBody has a unique “organ” the mantle Nervous system consists of a pharygeal ring and a two Nervous system consists of a pharygeal ring and a two

nerve chordsnerve chords ““Closed” circulatory systemClosed” circulatory system Coelom is reduced (three sections, one surrounds the Coelom is reduced (three sections, one surrounds the

heart, one the nephridia and the other the gonads)heart, one the nephridia and the other the gonads) Bilateral symmetry (may be “lost” in adult forms)Bilateral symmetry (may be “lost” in adult forms) Use cilia for movement (locomotion or to move water)Use cilia for movement (locomotion or to move water)





nerve chordsnerve chords Open circulatory systemOpen circulatory system Coelom is reduced (three sections, one surrounds the Coelom is reduced (three sections, one surrounds the






nerve chordsnerve chords ““Closed” circulatory systemClosed” circulatory system Coelom is reduced (three sections, one surrounds the Coelom is reduced (three sections, one surrounds the


Gastropods – IntroductionGastropods – Introduction

Snails, slugs and othersSnails, slugs and others The largest group of molluscs (over The largest group of molluscs (over

40,000 recent species described)40,000 recent species described) Large foot used for locomotion (usually)Large foot used for locomotion (usually) Posses a “radula” (used to scrape food Posses a “radula” (used to scrape food

in grazing snails, highly specialized in in grazing snails, highly specialized in some groups)some groups)

Shell is coiled – result of “torsion” Shell is coiled – result of “torsion” during larval developmentduring larval development


Only mollusk Only mollusk group to have group to have terrestrial formsterrestrial forms

Many species Many species have well have well developed eyesdeveloped eyes

Head often has Head often has tactile sensory tactile sensory appendagesappendages


Only mollusk group to have Only mollusk group to have terrestrial formsterrestrial forms

Many species have well developed Many species have well developed eyeseyes

Gas exchange via gills (most species) Gas exchange via gills (most species) or highly vascularized mantle cavity or highly vascularized mantle cavity or “lung” (pulmonate snails & some or “lung” (pulmonate snails & some terrestrial operculate snails)terrestrial operculate snails)

Gastropods – general formGastropods – general form

Gastropods - TorsionGastropods - Torsion

Gastropods – The radulaGastropods – The radula

Scraping tool Scraping tool used to feedused to feed

Common to all Common to all mollusks (except mollusks (except bivalves)bivalves)

May be modifiedMay be modified

Cone snails – ocean Cone snails – ocean predatorspredators

•In cone snails, the radula has been modified into In cone snails, the radula has been modified into “darts.”“darts.”

•When the snail senses prey (such as the hapless fish, When the snail senses prey (such as the hapless fish, above) the proboscis shoots out and one poison filled above) the proboscis shoots out and one poison filled dart harpoons the prey.dart harpoons the prey.

•The poison is a neurotoxin, that immobilizes the preyThe poison is a neurotoxin, that immobilizes the prey

•Cone snail venom may be fatal to humansCone snail venom may be fatal to humans

Gastropod VideoGastropod Video

Part 1 - Part 1 - http://www.youtube.com/watch?v=z6Z2XCdmEwU

Part 2 –Part 2 –http://www.youtube.com/watch?v=O0lLQLAvYFI&feature=related

Bivalves - IntroductionBivalves - Introduction

ClamsClams Over 15,000 Over 15,000

recent speciesrecent species Mostly marineMostly marine Common Common

inhabitant of deep inhabitant of deep sea thermal ventssea thermal vents

Freshwater formsFreshwater forms

Bivalves - IntroductionBivalves - Introduction

Only mollusks to lack Only mollusks to lack a radulaa radula

Classified based on Classified based on gill structuregill structure

Reduced headReduced head Laterally compressedLaterally compressed Hatchet-shaped footHatchet-shaped foot Adapted for Adapted for

burrowingburrowing

Bivalves – Life HistoryBivalves – Life History First larval stage is a First larval stage is a

trochophore trochophore (common to all (common to all mollusks)mollusks)

Morphs into veliger Morphs into veliger stagestage

Veliger morphs into Veliger morphs into juvenile (has same juvenile (has same form as adult)form as adult)

Juvenile grows by Juvenile grows by accretion at mantle accretion at mantle marginmargin

Bivalves - AnatomyBivalves - Anatomy

Time to look at Time to look at you “clam”you “clam”

Northern quahog Northern quahog Venus mercenariaVenus mercenaria

Bivalves - ExternalBivalves - External

Two valvesTwo valves Valves hinged on Valves hinged on

dorsal sidedorsal side Notice the growth Notice the growth

lines (concentric lines (concentric rings)rings)

Bivalves – Shell Bivalves – Shell Morphology & PhysiologyMorphology & Physiology

Most mollusks secrete a shellMost mollusks secrete a shell Shell is composed of calcium carbonate Shell is composed of calcium carbonate

(same material used by corals)(same material used by corals) Protected by periostracumProtected by periostracum Prismatic layer (crystals oriented vertically)Prismatic layer (crystals oriented vertically) Nacreous layer (crystals oriented Nacreous layer (crystals oriented

horizontally)horizontally)

Bivalves – Internal Bivalves – Internal Anatomy & PhysiologyAnatomy & Physiology

Teeth – keep shells Teeth – keep shells from slippingfrom slipping

Ligament – connective Ligament – connective tissue that contracts tissue that contracts when shell is openedwhen shell is opened

Adductor muscles – Adductor muscles – contract to allow the contract to allow the animal to “clam up”animal to “clam up”

Pallial line – attachment Pallial line – attachment point for the mantle to point for the mantle to the shellthe shell

Pallial sinus – shows Pallial sinus – shows position of the siphonsposition of the siphons

Bivalves – Internal Bivalves – Internal Anatomy & PhysiologyAnatomy & Physiology

Mantle – surrounds the Mantle – surrounds the body & apressed to the body & apressed to the shellshell

Contains sensory Contains sensory organs (tactile tentacle, organs (tactile tentacle, light sensing eye spotslight sensing eye spots

Secretes the shellSecretes the shell Is fused (two halves Is fused (two halves

joined) dorsally, open joined) dorsally, open ventrallyventrally

May be modified to May be modified to form siphonsform siphons

Bivalves – Anatomy & Bivalves – Anatomy & Physiology (Under the Physiology (Under the mantle)mantle)

FootFoot Primary form of Primary form of

locomotionlocomotion Animal pushes Animal pushes

foot into substratefoot into substrate Foot is filled with Foot is filled with

blood, causing it blood, causing it to expand and to expand and grip substrategrip substrate

Clam pulls body Clam pulls body toward foottoward foot


Gills (ctenidia)Gills (ctenidia) Respiratory Respiratory

functionfunction Secondary function Secondary function

is to filter water to is to filter water to capture foodcapture food

Gill structure is Gill structure is used to classify used to classify bivalvesbivalves

Bivalve gill evolutionBivalve gill evolution

Protobranchs Protobranchs (primitive)(primitive)

Bivalve gill evolutionBivalve gill evolution Protobranchs (primitive)Protobranchs (primitive) FilibranchsFilibranchs

Gills fold back to form a Gills fold back to form a “U”-shaped structure.“U”-shaped structure.

Mantle cavity divided by Mantle cavity divided by gills into a ventral gills into a ventral inhalent chamber and a inhalent chamber and a dorsal exhalent chamber.dorsal exhalent chamber.

Chambers connect to Chambers connect to outside via siphonsoutside via siphons

Gills filter food from the Gills filter food from the water passing across water passing across them.them.

Cilia move water across Cilia move water across the gills.the gills.



FilibranchsFilibranchs EulamellibranchsEulamellibranchs



FilibranchsFilibranchs EulamellibranchsEulamellibranchs SeptibranchiaSeptibranchia


Digestive SystemDigestive System Labial palps Labial palps

surround oral surround oral openingopening

Short esophagusShort esophagus StomachStomach Crystalline styleCrystalline style


The style – found in The style – found in many mollusksmany mollusks

Serves several Serves several functionsfunctions ““windlass” to pull windlass” to pull

food string from food string from esophagus to esophagus to stomachstomach

Stirring rodStirring rod Source of digestive Source of digestive

enzymesenzymes


Digestive SystemDigestive System Labial palps Labial palps

surround oral surround oral openingopening

Short esophagusShort esophagus StomachStomach Crystalline styleCrystalline style Intestine (loops Intestine (loops

around stomach)around stomach) RectumRectum


Circulatory SystemCirculatory System Pericardium encloses the Pericardium encloses the

heartheart Heart has two auricles Heart has two auricles

and one ventricleand one ventricle Circulatory system is Circulatory system is

open (blood passes from open (blood passes from arteries into sinuses in arteries into sinuses in the tissue and then back the tissue and then back into veins).into veins).

Most clams have Most clams have haemocyanin as the haemocyanin as the blood pigment. Some blood pigment. Some have haemoglobin.have haemoglobin.


Urogenital SystemUrogenital System Posses two nephridia Posses two nephridia

(similar to kidneys)(similar to kidneys) Most bivalves are Most bivalves are

dioeciousdioecious Gonads are usually Gonads are usually

adjacent to the adjacent to the intestineintestine

Gonads and nephridia Gonads and nephridia discharge to the discharge to the posterior portion of posterior portion of the mantle cavitythe mantle cavity

gastropods and pelecypods

Documents

molluscan bauplanbody

unique organ

mantlenervous system

pharygeal ring

adult formsuse cilia

movement locomotion

gonadsbilateral symmetry

extant species describedmarine