biology 320 invertebrate zoology fall 2005 chapter 12 – phylum mollusca part two

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Biology 320 Biology 320 Invertebrate Zoology Invertebrate Zoology Fall 2005 Fall 2005 Chapter 12 – Phylum Chapter 12 – Phylum Mollusca Mollusca Part Two Part Two

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Page 1: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Biology 320Biology 320Invertebrate ZoologyInvertebrate ZoologyFall 2005Fall 2005

Chapter 12 – Phylum MolluscaChapter 12 – Phylum Mollusca

Part TwoPart Two

Page 2: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Class GastropodaClass Gastropoda

Largest and most diverse Largest and most diverse class of molluscsclass of molluscs

Slugs, snails, and sea slugs Slugs, snails, and sea slugs

Only molluscs that live Only molluscs that live terrestriallyterrestrially– Mantle cavity is Mantle cavity is

modified to form lung in modified to form lung in somesome

Approximately 60,000 Approximately 60,000 described spp.described spp.

Page 3: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

All have some degree of torsionAll have some degree of torsion

Most have coiled shell Most have coiled shell

Much more active than polyplacophoransMuch more active than polyplacophorans

Higher degree of cephalization than Higher degree of cephalization than polyplacophoranspolyplacophorans– TentaclesTentacles– EyesEyes

Page 4: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

The Evolution of The Evolution of TorsionTorsion What is torsion?What is torsion?

– 180180° counterclockwise rotation of visceral mass, relative to foot° counterclockwise rotation of visceral mass, relative to foot

Possible benefits of torsionPossible benefits of torsion– Allows entire animal to fit inside shellAllows entire animal to fit inside shell

Visceral mass always protectedVisceral mass always protected Head and foot can be extended for feeding, locomotion, Head and foot can be extended for feeding, locomotion,

reproduction, etc.reproduction, etc. May be retracted for protection and to minimize water May be retracted for protection and to minimize water

lossloss

– Mantle cavity is located anteriorlyMantle cavity is located anteriorly May improve ventilation of gills / lungMay improve ventilation of gills / lung Osphradia can test water before animal moves forwardOsphradia can test water before animal moves forward

– Improved center of gravity for someImproved center of gravity for some

Page 5: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Possible costs associated with Possible costs associated with torsiontorsion– Sanitation problemsSanitation problems

Anus, nephridiopore, and Anus, nephridiopore, and gonopore located in close gonopore located in close proximity to mouthproximity to mouth

May foul mouth and gillsMay foul mouth and gills

Many have anatomical Many have anatomical adaptations to combat this adaptations to combat this problemproblem– Shell perforations, as in Shell perforations, as in

abaloneabalone– Anal pore at apex of shell, as Anal pore at apex of shell, as

in keyhole limpetsin keyhole limpets– Unidirectional water flowUnidirectional water flow

One gillOne gill Water enters on left and Water enters on left and

leaves on right side of mantle leaves on right side of mantle cavitycavity

Page 6: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two
Page 7: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Gastropod ShellsGastropod Shells Hollow cone coiled Hollow cone coiled

around an axis known around an axis known as a columellaas a columella

BaseBase

ApexApex

ApertureAperture– Opening though which Opening though which

head and foot can be head and foot can be extended / retractedextended / retracted

– Visceral mass stays Visceral mass stays inside shellinside shell

Page 8: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Oftentimes, aperture Oftentimes, aperture has a siphonal canal has a siphonal canal or notchor notch

SiphonSiphon– Anatomical Anatomical

adaptation for adaptation for respirationrespiration

– Portion of the mantle Portion of the mantle skirt that is rolled and skirt that is rolled and elongateelongate

– Allows snail to take in Allows snail to take in water and test before water and test before moving into itmoving into it

– Acts like a snorkel for Acts like a snorkel for burrowersburrowers

Page 9: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Complete revolution Complete revolution around columella is around columella is called a whorlcalled a whorl

Columellar muscleColumellar muscle– Retracts head and footRetracts head and foot– Originates at columellaOriginates at columella– Inserts at footInserts at foot

OperculumOperculum– Proteinaceous or Proteinaceous or

calcified disccalcified disc– Located on dorsal / Located on dorsal /

posterior footposterior foot– Seals aperture to Seals aperture to

protect against protect against predation and predation and desiccationdesiccation

Page 10: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Shell growth occurs when Shell growth occurs when edge of mantle secretes edge of mantle secretes organic materials and organic materials and minerals on lips of apertureminerals on lips of aperture

Growth lines can often be Growth lines can often be seenseen

Amazing diversity of shell Amazing diversity of shell shapes, patterns, and shapes, patterns, and colorscolors

Coloration comes from Coloration comes from pigments that are pigments that are synthesized, or synthesized, or sequestered from food sequestered from food items items

Page 11: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Shell shape is related to Shell shape is related to habitathabitat– Small spires = better Small spires = better

adapted for attaching adapted for attaching upside-down or vertically upside-down or vertically to rocks or aquatic to rocks or aquatic vegetationvegetation

– Long spires = moving Long spires = moving horizontally over soft horizontally over soft substratessubstrates

– Low / broad shells = Low / broad shells = clinging to rocks in strong clinging to rocks in strong currentscurrents

– Some, like moon snails, Some, like moon snails, have a muscular foot that have a muscular foot that facilitates burrowingfacilitates burrowing

Page 12: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Gastropod DiversityGastropod Diversity Three main groups:Three main groups:

– ProsobranchsProsobranchs– OpisthobranchsOpisthobranchs– PulmonatesPulmonates

No longer called Subclass Prosobranchia, Opisthobranchia, No longer called Subclass Prosobranchia, Opisthobranchia, and Pulmonataand Pulmonata

Recent uncertainty of classification Recent uncertainty of classification

Such diversity that it is easiest to point out specifics of each Such diversity that it is easiest to point out specifics of each groupgroup– Shell size, shape, colors and patternsShell size, shape, colors and patterns– Radula structure Radula structure – Feeding ecology Feeding ecology – ReproductionReproduction– Etc.Etc.

Page 13: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

ProsobranchsProsobranchs

20,000 spp.20,000 spp.

Most marine and Most marine and benthicbenthic

Few freshwater and Few freshwater and terrestrialterrestrial

Externally and internally Externally and internally tortedtorted

Marine limpets, Marine limpets, abalones, and snailsabalones, and snails

Page 14: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Shell may be coiled, or Shell may be coiled, or may posses one large may posses one large whorl like an abalone shellwhorl like an abalone shell

Snails posses an Snails posses an operculumoperculum

Respiratory systemRespiratory system– SiphonSiphon– Solitary left ctenidiumSolitary left ctenidium– MonopectinateMonopectinate

One kidneyOne kidney– Located on left sideLocated on left side– One nephridiopore empties into One nephridiopore empties into

mantle cavitymantle cavity

One gonadOne gonad– Right sideRight side– One gonopore empties into One gonopore empties into

mantle cavitymantle cavity

Page 15: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

CephalizedCephalized– Two cephalic tentaclesTwo cephalic tentacles– Typically posses one Typically posses one

lateral eye at the base of lateral eye at the base of each tentacleeach tentacle

ReproductionReproduction– GonochoricGonochoric– Some direct developmentSome direct development

Unique egg cases Unique egg cases molded by pedal gland molded by pedal gland of footof foot

– Some produce a veliger Some produce a veliger larvalarva

Possesses a swimming Possesses a swimming organ known as a velum, organ known as a velum, which consists of two which consists of two circular, ciliated lobescircular, ciliated lobes

Has a shellHas a shell

Page 16: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Size: a few mm to 70 cmSize: a few mm to 70 cm

LimpetsLimpets– Well adapted to clinging to rocksWell adapted to clinging to rocks– Travel up to five feet from Travel up to five feet from

“homes” and use homing “homes” and use homing behavior to returnbehavior to return

– Follow chemical cues from Follow chemical cues from mucus they secretemucus they secrete

– Mucus also stimulates algal Mucus also stimulates algal growth; they feed on algaegrowth; they feed on algae

AbalonesAbalones– Also well adapted for clinging to Also well adapted for clinging to

rocks, due to low / broad shellrocks, due to low / broad shell

Turban snailsTurban snails

Page 17: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

ConchsConchs

WhelksWhelks– CarnivoresCarnivores– Scavengers can detect carrion that Scavengers can detect carrion that

is 30 m awayis 30 m away– May wedge bivalves open using May wedge bivalves open using

the foot, and edge of aperture or the foot, and edge of aperture or siphonal canal siphonal canal

Moon snailsMoon snails– Some drill holes in the shells of Some drill holes in the shells of

bivalves, barnacles, and limpetsbivalves, barnacles, and limpets– Foot has a drill organ that drills for Foot has a drill organ that drills for

one minone min– Secretes acid into hole and lets it Secretes acid into hole and lets it

sit for 30 minsit for 30 min– Drills again to removed softened Drills again to removed softened

shellshell– May take 8 hr to drill through a 2 May take 8 hr to drill through a 2

mm thick shellmm thick shell

Page 18: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

DrillsDrills– UrosalpinxUrosalpinx – American – American

oyster drilloyster drill– Can decimate oyster bedsCan decimate oyster beds

Cone snailsCone snails– Carnivores of polychaetes, Carnivores of polychaetes,

gastropods, and fishgastropods, and fish– Tropical – live in Indo-Pacific Tropical – live in Indo-Pacific

and Western Atlanticand Western Atlantic– Highly modified radulaHighly modified radula

One radular tooth bathed in One radular tooth bathed in and filled with neurotoxic and filled with neurotoxic venomvenom

Everted like a harpoonEverted like a harpoon Tooth replacedTooth replaced

– Occasional human deaths Occasional human deaths from cone snail venomfrom cone snail venom

Page 19: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

OpisthobranchsOpisthobranchs

3000 marine spp.3000 marine spp.

Interstitial to 60 cm in lengthInterstitial to 60 cm in length

DetortedDetorted– Also seen in the nervous Also seen in the nervous

systemsystem– Therefore, they are Therefore, they are

essentially bilaterally essentially bilaterally symmetricalsymmetrical

Reduction / loss of mantle Reduction / loss of mantle cavitycavity

Reduction / loss of shellReduction / loss of shell

Modern species lack operculaModern species lack opercula

Page 20: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Because they lack a shell, Because they lack a shell, opisthobranchs have opisthobranchs have developed other defensesdeveloped other defenses– Sequester nematocysts for Sequester nematocysts for

defensedefense

– Some have lateral Some have lateral expansions of the foot expansions of the foot (called parapodia) that they (called parapodia) that they use for escape swimminguse for escape swimming

– Often have skin glands that Often have skin glands that produce sulfuric acid or produce sulfuric acid or other noxious substances other noxious substances that repel fish and other that repel fish and other predatorspredators

– Aposematic colorationAposematic coloration

– Cryptic colorationCryptic coloration

Page 21: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

GillsGills– Absent in someAbsent in some– When present are unlike When present are unlike

prosobranch gillsprosobranch gills– Gill SA is provided by mantle Gill SA is provided by mantle

folds folds – May be located on body May be located on body

surface in some (anal gills or surface in some (anal gills or cerata)cerata)

Nervous systemNervous system– Trend towards cephalization Trend towards cephalization

and detorsionand detorsion– Cephalic tentaclesCephalic tentacles– RhinophoresRhinophores

Second pair of tentacles, just Second pair of tentacles, just posterior to the firstposterior to the first

ChemosensoryChemosensory Can be retracted into a sheathCan be retracted into a sheath

Page 22: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

ReproductionReproduction– Simultaneous Simultaneous

hermaphroditeshermaphrodites– Reciprocal internal Reciprocal internal

fertilizationfertilization– Eggs usually oviposited in Eggs usually oviposited in

gelatinous stringsgelatinous strings– Veliger larvae or direct Veliger larvae or direct

developmentdevelopment

Bubble snailsBubble snails– Also called bubble shellsAlso called bubble shells– Still have a shell, Still have a shell,

although somewhat although somewhat reducedreduced

– Superficially resemble Superficially resemble sea slugssea slugs

– Most primitive of the Most primitive of the opisthobranchsopisthobranchs

Page 23: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Sea HaresSea Hares– Largest opisthobranchs Largest opisthobranchs

(up to 60 cm)(up to 60 cm)– Resemble sea slugsResemble sea slugs– Shell is reduced (in Shell is reduced (in

mantle) or absentmantle) or absent– Some swim with Some swim with

parapodia, or by jet parapodia, or by jet propulsionpropulsion

– Some release purple ink Some release purple ink when disturbedwhen disturbed

PteropodsPteropods– Sea butterfliesSea butterflies– Swim using large Swim using large

parapodiaparapodia– Small; some posses a light Small; some posses a light

shellshell– Some conduct gas Some conduct gas

exchange across body exchange across body surfacesurface

Page 24: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

NudibranchsNudibranchs– Sea slugsSea slugs– Graze on cnidarians Graze on cnidarians

and sequester and sequester nematocysts or nematocysts or photosynthetic photosynthetic endosymbiontsendosymbionts

– Lack shell and Lack shell and mantle cavitymantle cavity

– Sometimes lack gillsSometimes lack gills– Cerata Cerata

Function as gillsFunction as gills Sites for nematocystsSites for nematocysts Each contain a branch Each contain a branch

of digestive cecumof digestive cecum

Page 25: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

PulmonatesPulmonates 16,000 – 30,000 spp.16,000 – 30,000 spp.

PrimitivePrimitive– Intertidal and freshwater Intertidal and freshwater

snails snails – Intertidal and freshwater Intertidal and freshwater

limpetslimpets

ModernModern– Terrestrial snails, and slugsTerrestrial snails, and slugs

DetorsionDetorsion

Slugs lack shellsSlugs lack shells– Original distribution center of Original distribution center of

slugs has low soil calciumslugs has low soil calcium

Pulmonate snails lack an Pulmonate snails lack an operculumoperculum

Page 26: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Mantle cavity on right side, but no gills; mantle Mantle cavity on right side, but no gills; mantle cavity converted to a lungcavity converted to a lung

Opening to lung is termed pneumostome Opening to lung is termed pneumostome

Roof of mantle cavity is highly vascularizedRoof of mantle cavity is highly vascularized– Capillary bedCapillary bed

Floor of cavity is elevated and depressed to Floor of cavity is elevated and depressed to ventilateventilate

Page 27: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Physiological adaptations Physiological adaptations to terrestrial existenceto terrestrial existence

– Secrete a mucus plug that Secrete a mucus plug that acts like an operculumacts like an operculum

– Secrete mucus Secrete mucus Prevents desiccationPrevents desiccation Defends against bacteriaDefends against bacteria Discourages predatorsDiscourages predators Facilitates locomotionFacilitates locomotion

– Uricotelic instead of Uricotelic instead of ammonotelicammonotelic

– Tolerant to water lossTolerant to water loss HelixHelix can lose 50% of body can lose 50% of body

waterwater 80% in 80% in LimaxLimax

Page 28: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Behaviors associated with Behaviors associated with terrestrial existenceterrestrial existence– Periods of torpor during unfavorable Periods of torpor during unfavorable

weatherweather Estivation during hot / dry weatherEstivation during hot / dry weather Hibernation during cold weatherHibernation during cold weather

– Most inhabit humid environmentsMost inhabit humid environments

– Those living in xeric environments Those living in xeric environments are only active at night or after rainsare only active at night or after rains

Page 29: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

Most are herbivorous, Most are herbivorous, and some are serious and some are serious crop pestscrop pests

Many have been Many have been introducedintroduced– Giant African snail has Giant African snail has

been introduced to Hawaii been introduced to Hawaii and continental U.S.and continental U.S.

Up to 23 cm in heightUp to 23 cm in height

Second largest group of Second largest group of snails can reach 15 cm snails can reach 15 cm and are found in South and are found in South AmericaAmerica

Page 30: Biology 320 Invertebrate Zoology Fall 2005 Chapter 12 – Phylum Mollusca Part Two

HermaphroditesHermaphrodites

Reciprocal internal fertilizationReciprocal internal fertilization– Could be considered an adaptation to terrestrial lifeCould be considered an adaptation to terrestrial life– Many deposit spermatophoresMany deposit spermatophores

Direct developmentDirect development

Interesting courtship ritualsInteresting courtship rituals– Twist around a mucus strand in LimaxTwist around a mucus strand in Limax– Love darts in HelixLove darts in Helix