The Website for Houston Mollusks
Your Subtitle Text
Malacology: an overview

This is a basic introduction to Malacology, including foundational concepts, classifications, and anatomical terms. 

What is Malacology?  Malacology is the study of mollusks. 

What are mollusks?  The phylum Mollusca includes such soft-bodied invertebrates such as snails, clams, oysters, and squid.  Most seashells were once living mollusks. 

Why study Malacology?
   The field of Malacology is not a very well known branch of science, yet it plays an important role in biological ecosystems all over the world.  Studying mollusks helps scientists understand some of the most complicated problems of this century, such as cellular cancer and pollution control. 

What good are mollusks?    Mollusks provide a vast array of uses and benefits.  They are an enormous source of food for both humans and animals;  their shells can be used to make tools and implements, and are also used as a calcium supplement.  Bivalves filter out toxic waste out of the water, and Cone Shell venom is used as medical serum.  There is even a snail whose large cellular structure is being used to test cures for cancer.  Here's a list of the uses for mollusks:

Food- escargot, calamari, shellfish, etc.

Tools/weapons- tough shells make rudimentary implements

Roadwork- crushed shell used to pave streets

Decoration- abalone shell (mother of pearl), seashells, pearls

Clothing-  mussel shell buttons, purple dye (Murex sp.)

Medical- Calcium supplements, disease and cancer research

Pest control- carnivorous snails prey on harmful pest species

Pollution control- Bivalves filter toxins from water

Horticulture- many snails and slugs recycle dead plants to create a natural fertilizer

Aquarium trade- aquatic snails look pretty and eat algae off the glass

Religion- Jewish culture uses Murex trunculus to create a special, sacred blue dye for tassels

Currency- some shells used as money in certain countries

 Classifying Mollusks

The Phylum Mollusca

All mollusks are classified under the phylum Mollusca.  There are six classes of mollusks:

1. Class Cephalopoda

This class includes the highly intellegent, many-armed orders of mollusks.  These are only found in marine environments.  Each animal has at least eight arms, and some have two additionial tentacles.  Squids have a rigid internal structure called a pen, and cuttlefish have an internal shell called a cuttlebone.  Nautili have an external shell.  Octopi have neither.  All cephalopods have a parrot-like beak with which they dismantle their prey (squid will bite if handled). These animals are so intelligent, they are used by scientists to study how the brain learns and works.  

- Octopus
- Squid
- Cuttlefish
- Nautilus
- Argonaut
- Spirula

2. Class Gastropoda

This is the largest class of mollusks, and includes those with either one or no external shell on the dorsal side.

- Land/Freshwater snails
- Slugs
- Marine snails
- Pteropods
- Nudibranchs

3. Class Monoplacophora

This class contains gastroverms, mollusks with a single dorsal shell and an esposed ventral side.  These live on rocks in the deep sea.  If one senses danger, it will seal itself to a rock to protect itself, often requiring many hundreds of pounds of pressure to remove.


4. Class Pelecypoda

This class encompasses the two-halved, hinged shell variety of mollusks known as Bivalves.  These are strictly aquatic.

- Oysters
- Mussels
- Clams
- Scallops
- Cockles

5. Class Polyplacophora

This class includes mollusks with jointed dorsal armor which live on tidal rocks.  Each animal has eight armored plates on its back which protect it from predators.  In the event of an attack, it clings tightly to the rock face.

- Chitons

6. Class Scaphapoda

This class includes the small, tooth-shaped mollusks which live buried under mud in the ocean. Some species live at depths of over 15,800 feet.

- Tusk Shells

- Deep-sea Cadulus

Classifying Landsnails

Land snails, which are what is primarily focused on, are categorized as Pulmonates under the class Gastropoda. There are three orders of gastropods:

These mollusks are marine sea slugs, most of which lack external shells. Some of these animals have bright colors and stinging cells. 
- Nudibranchs
- Sea Hares
- Bubble Shells
- Pteropods
(sea butterflies)

This is the order involving marine snails. These mollusks are prized by collectors for their beautiful shells. Most marine snails have an operculum.

- Whelks
- Conchs
- Tritons
- Volutes
- Cowries
- Murex

Pulmonates are distinguished by the fact that their mantle cavity can be used as a lung.  Order Pulmonata includes aquatic and terrestrial snails and slugs. 

- Land Snails
- Pond Snails
- Slugs

Anatomical Terms

Aperture-  The opening of a univalve shell.

The top or peak of the dorsal side of a univalve shell.

Comnunella-   The spiraled column that runs up the center of shells, kind of like the center column of a spiral staircase. 

Mantle-   This part of the body differs in function for each type of mollusk: in gastropods, it is a sheet-like organ that covers the viceral mass, contains organs, and secretes calcium onto the shell; in bivalves, it is most recognizable as the part that is eaten; in cephalopods, it is the sac or tube that contains internal organs and serves as a cranium.

A tough, corneous, trapdoor-like object that covers a shell's aperture and protects the animal when it retracts into its shell. Found only in some gastropods.

A thin, filmlike layer that covers the surface of many shells, and gives some their color.  It is comprable to the periosteum that covers bones.

Radula-   A tongue-like organ with thousands of tiny teeth which certain mollusks use to rasp away at their food.  It's like a belt with teeth, or a cheese grater. 

Umbilicus-  The hole that is formed by the inside of the comnunella that runs up the center of a univalve shell, open at the anterior end and ending at the posterior, or apex. 

   The twisting form of a gastropod shell; the number of whorls depends on how many times the shell twists around in a complete circle. 
Website Builder