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  Hello my name is Gerry Gastropoda and I'm here to tell you about my very big Class. I am a member of the class scientists call Gastropoda. In Latin, this means stomach foot. My class is further divided into three very important subclasses representing over 40,000 known species living today. My large class of molluscs holds approximately 75 to 80 percent of all the known living molluscs.

My three subclasses are as follows:

The Prosobranchia: This is the biggest of the subclasses and contains most of the mollusc seashells that people recognize and pick up along our beaches. Most of the members here are marine inhabitants, or in other words, they live only in salt water. However, many of the members can also live in freshwater or even on land (terrestrial). Every member of this big subclass has a coiled shell. Their soft bodies have a head complete with two eyes located on the tops of two tentacles. These cousins of mine all breath by means of gills. They have a big flat foot, which they use for locomotion and on the back end of this foot is a structure called an operculum, which acts as a trap door. When a prosobranch is threatened by an enemy or he is afraid of getting dried-out (all molluscs must keep moist to stay alive), they pull all their soft, moist body into their shell then they close the operculum behind them just as you close the door to your house.

Most of the seashells you people collect along beaches or lakes are from the members of this subclass. Some of the families in this subclass are known by names such: conchs (Strombidae), whelks (Buccinidae), limpets (Fissurellidae), periwinkles (Littorinidae), cones (Conidae), murex (Muricidae), volutes (Volutidae), and cowries (Cypraeidae).


Stombus gigas
(Linnaeus, 1758)
Queen Conch

Neptunea lyrata
(Gmelin, 1791)
New England Neptune

Diodora aspera
(Rathke 1833)
Rough Keyhole Limpet

Littorina angulifera (Lamarck,1822)
Angulate Periwinkle


Conus marmoreus
(Linnaeus, 1758)
Marble Cone


Chicoreus ramosus
(Linnaeus, C., 1758)


Cymbiola imperialis
(Lightfoot, 1786)
Imperial Volute

Cypraea cribaria
(Linnaeus, 1758)
Sieve Cowrie
The Opisthobranchia: All of the members of this subclass are marine inhabitants. Most members in this sub-class only have a very small, fragile shell and it is often contained right inside their soft bodies or they may not have a shell at all. Most of these cousins of mine breathe through their gills; however, some absorb oxygen from the water directly through a specialized membrane (something like the thin skin lining the insides of your cheeks) lining their mantle cavity.

Many of these molluscs have very colorful bodies. We know some of the Opisthobranches as: sea hares, sea  butterflies (Thecostoma), sea slugs (saccoglossans and nudibranchs), and canoe (Scaphandridae) and bubble shells (several families).

Sea Hare

Aplysia parvula

(Guilding in Morch, 1863)
Sea Hare

Sea Butterlies

Diacavolinia longirostris
(Blainville, HMD de, 1813)
Long-snout Cavoline
Dirona albolineata
(MacFarland in Cockerell & Eliot, 1905) 150
Alabaster dirona
Bubble Shell

Hydatina amplustre
(Linnaeus, 1758)
Royal Paper Bubble

The Pulmonates: These are my woodland and garden dwelling snail and slug cousins. Most of these molluscs live on land or in freshwater lakes and streams; however a few are marine dwellers. They all breathe by means of pulmonary sacs not gills.

Some have coiled shells, but many do not have a shell at all. One very interesting fact about most pulmonates is, the members of this subclass are both male and female (hermaphrodites) at the same time.

This comes in very handy as these snails are very slow moving and don t like moving around too much. If they had to go looking for a boyfriend or girlfriend, it could take them a very, very long time to have babies. Being both male and female solves this problem. When they come across another snail of their kind, they just exchange sperm packets with each other and then they both go off and lay eggs. Baby molluscs hatch out some time later and they too are born as both boy and girl within the same slug or snail body.

Land Snail

Helix pomatia
(Linnaeus, 1758)

Freshwater Snail

Planorbis planorbis
(Linnaeus 1758)
Ramshorn Snail


Ariolimax columbiana
Pacific Banana Slug

Picture coutesy of
Dr. Robert Thomas and Margaret Orr
© 2001
California Academy of Sciences
more information

Here are some very interesting gastropod facts:
  • When we hold a large seashell up to our ear, we can hear the sound of the seashore waves because the shell echoes and jumbles all the sounds around us!

  • All cone shells possess a poisonous dart (a modified radula) with which they harpoon, inject venom and thus kill their prey. Some cone shell possess venom is so toxic that if stung, it can severely harm or even be fatal to man.

Conus striatus

(Linnaeus 1758)
Striate Cone
  • Many land snails can lift ten times their own weight up a vertical surface (like a wall).

  • Many members of the Carrier shell family collect seashells. These shells scientists call Xenophoridae attach other shells or stones to their own shell for protection and camouflage. Sometimes they even use man-made objects such as glass and bottle caps!

Xenophora pallidula

(Reeve, 1842 )
Pallid Carrier-shell
  • The largest snail (univalve) known attained a length of 78 cm (two and one half feet) with a girth of nearly forty inches. This trumpet conch, Syrinx aruanus (Linneus, 1758), weighed in at nearly forty pounds.

Syrinx aruanus

(Linnaeus, C., 1758)
Australian Trumpet
  • The largest land snail known is the Giant African Land Snail. It can weigh up to 2 pounds (900g) and attain a length of 15.5 inches (39cm) from head to tail.

Achatina fulica
(Bowdich, 1822)
The Giant African Landsnail
  • The smallest known snail shell is the Ammonicera rota and measures only 0.02 inches in diameter.  Fifty of them laid end to end would measure one inch!

  • Pelagic gastropods live their entire life without ever touching bottom or shore! They float and travel on the ocean s currents. The violet snail, the Janthina, can travel hundreds of miles in their lifetime as they float around on the ocean s currents. These delicate shells only touch land when they get washed

Janthina janthina
(Linnaeus, 1758)
Common Purple Sea Snail

up onto beaches during storms. An unsuspecting person when picking up these shells and animal, which look like a piece of purple bubble gum, will get dyed a pretty purple colour. This is a dye the animal uses for protection against its enemies.

  • Some snails live in the very tops of trees, while others live high up in the mountains or even in deserts.  Some may be living in your own back yard wherever you live.

  • The common garden snail, Helix aspersa Linneus, can travel about two feet (600mm) in three minutes. At that rate, it would travel 1500m (one mile) in five and one half days - a true "snail's pace"



Helix aspersa

(Müller, 1774)
Brown Garden Snail

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