1

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!!!

2

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

3

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

4

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

5

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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

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

14

Gastropoda

• Conus – Cone shells• Tropical marine• Radula modified as a

dart, usually venomous.

• Feed on wormsand mollusks