Gastropod

CLASS GASTROPODA

Gastropods are the most important class of the phylum Mollusca as they make up about 80% of the mollusk species. They can also been seen as the most 'successful' class, since they inhibit almost all the habitats.

Some examples of this class include snails, slugs, nudibranch, sea butterflies, and etc.

Feeding:

There are many types of feeding for gastropods. For the marine gastropods, there are carnivores, herbivores, and detritus feeders. For herbivores, the radula is used to scrape the algae off rocks and twigs in the water or to eat buds, roots, flowers and plants on land. Carnivores use radula to drill hole in the shells of other animals and then extend the radula into the shell to tear up and swallow the soft tissues.

Respiration:

The marine gastropods breath through their gills that's inside their mantle cavities, but the land snails and slugs breathe through a special mantle cavity that is lined with many blood vessels. The surface has to be moist so the oxygen can enter the cells. Therefore most land snails and slugs live in moist places to avoid losing water to dry air.

Digestion:

After food has been taken in by the radula, ciliary currents or muscle contractions will transport food through the digestive tract to the stomach where digestion takes place. The food will then be broken down by the enzymes secreted by the salivary and digestive glands.

Circulation/Internal Transport:

Gastropods have an open circulatory system in which blood is pumped by a heart. Since not all blood will be contained in blood vessels, some will travel through the body tissues in spaces called sinuses, which will lead to the gill (where oxygen and carbon dioxide are exchanged) and back to heart. The nutrients obtained by digestion will be carried throughout the body by blood.

Excretion:

Undigested food will become feces that are eliminated through the anus, and nitrogen-containing waste, ammonia that resulted from the cellular metabolism will be removed from the body fluid through the tube-like nephridia.

Adaptation/Response to environment:

Most of the gastropods have a one piece shell, called protoconch, that is spiraled or coiled and usually opens at the right hand side. They all have a definite head with 2 or 4 sensory tentacles. When they feel threatened, they will curl up into their shells for protection. Some will even have an operculum, a hard disk that’s located on their foot, to help them close their opening, the mouth. However, for other species, like slugs and nudibranchs, that don’t have shells, they use other methods for protection. Slugs usually hide under logs and rocks in broad daylight to avoid predators. Sea butterflies will swim quickly away from danger. Sea hares use their special ink sac to squirt ink into the water and confuse the predator while they get away. Nudibranch collects the nematocysts from the cnidarians they ate and will release them when being threatened. Their bright coloring also keeps the predators away as they warn the predator of their poison.

Movement:

The word gastropoda means stomach foot. It's quiet accurate, since most of the gastropods move with their broad and muscular foot located on their ventral side. The advantage of this type of movement is that they can be attached firmly to the surface using their muscular foot. However, the disadvantage shows in their slow movements, making it harder for them to escape predators.

Reproduction:

Gastropods' reproduction varies, but most of them have separate sexes and reproduce sexually. External fertilization occurs for most of the marine gastropods, while a few have internal fertilization. Some gastropods are hermaphrodites and some are even protandric hermaphrodites (male first and then become female as they age).

Anatomy of Snail