BIO 222 Invertebrate Zoology II Fall 2004 Dave Dyer Quaternary Sciences Program Northern Arizona University Lecture 14 Gastropoda Gastropoda • Why study them? • Integral part of the nutrient cycle • Poorly studied • Food source • Disease and parasite vector • Unique Bauplan • Rich fossil record • Pretty!!!
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BIO 222Invertebrate Zoology II
Fall 2004
Dave DyerQuaternary Sciences ProgramNorthern Arizona University
Lecture 14
Gastropoda
Gastropoda
• Why study them?• Integral part of the nutrient cycle
• U-shaped gutGills or CtenidiaSensory patches or osphradia Anus Mantle Reversed
Gastropoda
• Torsion• Independent of shell spiral• Two-stage process – takes place in veliger• 1st stage occurs in minutes to hours rotating 90°• 2nd stage occurs more slowly as a result of tissue
growth
• Detorsion• In some gastropods, torsion is reversed 90° to 180°• Common to Opisthobranchia
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Gastropoda
• Organ loss• Result of torsion• Left side enhanced – Right side reduced or
absent• Why?• Speculation – allows for retraction of foot and
head into mantle cavity in the shell in veligerform – Walter Garstang, zoologist – 1928
Gastropoda
• Speculation – allows more room for retracting foot and head in adult form and move sensory structures anteriorly
• Speculation – allows growth of shell in alignment with foot rather to one side
• Nobody knows!!! Opportunity?!?!
Gastropoda
• Ancestor bilaterally symmetrical• Asymmetry due to torsion and shell coiling• Shell characteristics
• Calcareous• Usually coiled around
a columella• Shell may coil right
(dextral) only, left(sinistral) only, orright or left
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Gastropoda
• Ancestral shell was probably planospiral• Living examples; Planorbis – Ram’s Horn
Snail (freshwater living on vegetation) and Nautilus (marine, free- swimming)
• Problem? cumbersome
Gastropoda
• Multiple layers• Outer layer periostracum
made of conchin• Shell secreted by mantle at lip of terminal
whorl aperture• Nacre?• Why a shell?• Protection and
support of visceral mass
Gastropoda
• Shell nomenclatureApex or protoconch
Whorl
Terminal or body whorl
Suture
Aperture with operculum
Siphonal notch
ColumellaAperture lip
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Gastropoda
• Radula Characteristics• What’s a radula?• Primarily feeding as
scraping or shredding• Abrasive, extendable
structure• May contain up to
250,000 teeth• Other feeding adaptations –
ctenidia?!?! Filter feeding as in sea butterflies
Urosalpinx
Gastropoda
• Reproduction• Dioecious or
hermaphroditic• Nephridium and
gonoduct mergeto form aurogenital ducttransporting bothurine and gametes
Gastropoda
• Reproduction• Gonads are
both ova andtestis - ovotestis
• Spermtransferred only
• Simultaneous orsequentialhermaphrodites
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Gastropoda
• Reproduction• Trochophore larvae
called a veliger• May develop within
egg sac
• Egg sacs, egg massesor planktoinc
Gastropoda
Gastropoda
• Order Archaeogastropoda• Ancestral group• Radula modified for
herbivory• Scrapers and shredders
• Calcareous shellwith nacre andoperculum
• Virtually all marine
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Gastropoda
• Haliotis – Abalone or Paua shell• Tightly coiled shell• Nacreous• Water flow through
openings in shell• Widely distributed• Gametes distributed
into water column
Gastropoda
• Megathura – limpets• Shell not coiled• Keyhole is
excurrent porefor water flow
• Radula a scraperfeeding on algae
• Reproduction similar to abalone
Gastropoda
• Astraea – Turban shell (also Greek goddess of innocence and purity)• Spiral coiled• Operculum present• Radula as scraper• Algae feeder
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Gastropoda
• Nerita – Nerites shell• Very common, often used to make shell
chandeliers• Radula as scraper, algae feeder
Gastropoda
• Order Mesogastropoda• Marine, freshwater and terrestrial• Porcelaneous, nonnacreous• Cornified operculum• Cephalic tentacles,
basal eyes• Radula with marginal
teeth, mostly forherbivory but also fordrilling
Gastropoda
• Littorina – Periwinkle shell• Rocky shore splash zones• Can live in air for
several weeks• Operculum present• Edible• Worldwide distribution
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Gastropoda
• Turritella – Tower shells• Sub- tidal to tidal zone• Feed in the mud with
mucous sheets on gills• Very high spired shell• With operculum• Abundant in fossil record
Gastropoda
• Cerithium – Cerithium shell• Shallow marine on
multiple substrates;mud, sand, rocky
• Larvae planktonic• Operculum present• Capture food in
gill nets
Gastropoda
• Strombus – Conch shells• Distinct notch at front of shell
that eyes protrude through• Keen eye sight• Small operculum• Important regional