Gastropoda - Northern Arizona Universitybio222-c/LecturePDFs/Lec 14.pdf · Gastropoda • Strombus...
Transcript of Gastropoda - Northern Arizona Universitybio222-c/LecturePDFs/Lec 14.pdf · Gastropoda • Strombus...
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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
• Poorly studied
• Food source• Disease and parasite vector• Unique Bauplan• Rich fossil record• Pretty!!!
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Gastropoda
• Let’s review…
Gastropoda
• Greek for gaster “stomach”; pous “foot”• Sea slugs, snails – marine, freshwater and
terrestrial• 37,500 – 80,000 living species – largest class of
Mollusks; second only in number to Arthropods• ~15,000 fossil species• Size range from 14 kg (California Black Sea
Hare) to 0.01 g (Vertigo)
Gastropoda
• Diverse habitats• Marine – tidal margins to deep ocean• Freshwater – bottom dwellers, vegetation• Terrestrial – arid environments, rain forests,
arboreal and rock talus to 11,000 ft.• Invasive
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Gastropoda
• 3 subclasses• Prosobranchia - shelled
• Marine, freshwater and terrestrial
• Opisthobranchia – shell- less• Marine – sea hares and nudibranchs
• Pulmonata – shelled and shell- less• Freshwater and terrestrial
• Terminology
Gastropoda
• Subclass Prosobranchia• proso “forward”; branch “gill”• Torsion
• Viscera rotated 180°counterclockwise
• Mantle cavity, gillsexcretory, genitalopenings areforward
• 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
food source• Unique hopping motion
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Gastropoda
• Strombus• Internal fertilization
then sand coveredegg mass
• Warm shallow marine• Carnivorous
• Feed on bivalves
• Cameos made from conch shell
Gastropoda
• Polinices, Natica – Moon shells• Carnivorous – feed
on clams• Body often too large
to retract into shell• Toothed radula• Widely distributed
Gastropoda
• Cypraea – Cowrie shells• Mantle extends over shell• Shallow marine• Feed primarily on
sponges• Dissolves old whorls
to use in new ones
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Gastropoda
• Order Neogastropoda• Most derived• Porcellaneous shell• Radula modified for
carnivory• Long anterior notch
Gastropoda
• Murex, Hexaplex, Muricanthus• Tropical marine• Feeding on bivalves,
limpets, other mollusca• Secretes a softening agent
during drilling(calcium chelatingcompound)
Gastropoda
• Thais, Acanthina, Neorapana• Worldwide distribution• Feed on mollusks• Shallow marine
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Gastropoda
• Buccinia, Babylonia, Busycon – Whelks• Shallow marine• Widely distributed• Feed on mollusks• Unique egg sac• Often sinistral
Gastropoda
• Melongena• Shallow marine• Feed on barnacles• Some covered with
hair that collects sandgrains forcamouflage
• Tolerant of low salinity• Eggs deposited on rocks
Gastropoda
• Olivella – Olive shells• Warm, tropical marine• Mantle completely
covers shell• Burrow in sand• Feeds on worms,
bivalves and crabs• Found in many archaeological sites• Used for exchange and jewelry