More on Gastropods

Gastropods are the largest group of mollusks with 37,500 different species, which vary from land and water-dwelling types. Gastropods are more commonly known as snails or slugs.

In Greek, gastro means "stomach" and poda means "foot", and combined, "stomach-foot" seems to represent the way that snails or slugs crawl on their stomachs. However, gastropods' stomachs and digestive system is located on the other side of their bodies.

The above illustration is that of a land, air-breathing snail and varies from other gastropods. While this land snail has lungs to breathe through, gastropods in water habitats have gills. All gastropods have an open circulatory system in which blood is pumped through the heart to the gastropod's blood vessels and then the blood enters the body cavities, surrounding the organs and directly providing nutrients and oxygen to the gastropod's tissues (a process also known as diffusion).

The snail is able to move by creeping on a flat "foot" underneath the body (see above diagram).
This "foot" is made up of muscle tissue and its contraction and expansion created a rippling movement that pushes the snail forward. This "foot" also has a special gland which produces mucus to make a slippery track. This track not only allows the snail or slug to move faster, but also provides protection to the gastropod's underside.

Gastropods (which can be both herbavores and carnivores) also have a radula in its mouth which is used for grinding up its food. This radula is like a rough tongue, which it uses to scrape or cut food before entering the gastropod's esophagus.

Gastropods posses a digestive system includes the buccal mass, esophagus, stomach, intestines, and hepatopancreas. The bucal mouth consists of the mouth and pharynx. The mouth of the gastropods opens into an espohagus which acts as a connector to the stomach. Two glands open into the stomach and secrete enzymes which help break down the food. The hepatopancreas produces these enzymes as well as absorbing and storing the nutrients from the food. Gastropod's digestive tract is twisted and coiled so that the anus of the animal is located above its head.

Gastropods also have sensory organs, the upper pair of tentacles located on the head have primitive eyes on the tips of them. However, the main sensory receptors are the olfactory organs which allow the gastropods to smell and these are located on the smaller, lower pair of tentacles.

Some gastropods are hermaphroditic while other species have two different sexes, thus varying the forms of reproduction. When the gastropods are about 3 years old, they are able to lay eggs. Snails are able to lay eggs up to six times a year and can lay an average of 85 eggs. These eggs hatch in 2 to 4 weeks, depending on the temperature and moisture level in the soil. The eggs are usually small and white or yellowish. Snails conceal their eggs with a mixture of soil and mucus. The first thing newly-hatched gastropods do is to find food. It will usually eat what is left of its eggshell or even any eggs that have not hatched yet. If the gastropod has a shell, then its shell grows too, in a spiral shape. The part of the shell the baby is born with ends up in the middle of the spiral since new shell is added at the opening. Gastropods have a varying life span, ranging from 5 to 15 years. Some gastropods, such as land snails hibernate in the winter, by closing up the entrance of their shell with a door of slime which hardens into a tough skin.