The Zone Without A Backbone

Phylum:

• Mollusks belong to the phylum Mollusca.

General characteristics:

• Generally, mollusks are soft bodied invertebrates with no body segments.
• They have bilateral symmetry.
• Their bodies are often covered with an outer shell.
• All mollusks have a muscular foot that has different functions.
• They all have a mantle which covers their internal organs and produces a hard shell.
• Some mollusks have large eyes and brains.
• Their digestive system has two openings, the mouth and the anus.

Respiration:

• All mollusks breathe through their gills.

Circulatory System:

• Most mollusks have an open circulatory system, in which blood is not in vessels, but cephalopods are so big, they need a closed circulatory system.

Classification:

• Mollusks are classified based on their type of foot, their presence of shell, their type of shell, and their type of nervous system.

The Three Different Types:

• There are three different types of mollusks; gastropods, bivalves, and cephalopods.
• Examples of gastropods are snails and slugs. Most gastropods have a shell but some don't. Gastropods are herbivores, scavengers, and carnivores. They use a radula to tear through plants and to bore a hole in an oyster's shell. Gastropods live in oceans, on rocks and land, and even in freshwater. Gastropods are able to move because of a broad muscular foot. They use the foot to creep along a carpet of mucus that they ooze out so it is easier to crawl along the ground. Gastropods make up approximately 80% of all mollusks.
• Some examples of bivalves are oysters and clams. Bivalves always have two shells that are held together by hinges and strong muscles. Bivalves filter feed. The food sticks to the mucus on their gill, then cilia move the food to the mouth. Some bivalves are omnivores, however, so they eat bacteria and protists. Bivalves live in any and all watery environments. Bivalves larvae are able to swim and float around, but adults usually stay where they are, but they can use their foot to move quite slowly. Bivalves have two shells with hinges and strong muscles. They are the only mollusks lacking a radula.
• Examples of cephalopods are octopi, squids, and nautilus. Cephalopods usually have an internal shell, but some have an external, and some have no shell at all. Cephalopods are carnivores. They capture prey with their muscular tentacles, then crush the prey with their beak, and finally scrape the flesh off with a razor-sharp radula. All cephalopods are ocean-dwelling. Cephalopods move by jet propulsion. They squeeze a current of water out of the mantle cavity and through a tube. Cephalopods are the fastest of all mollusks. Cephalopods have a closed circulatory system, which allows them to be the fastest, smartest, and biggest mollusks.

Importance of mollusks:

• Mollusks are important because they are food for humans and other animals. They are used for pearls and native american currencies. Because some mollusks filter water, they are a good environmental indicator. Many mollusks can cause property damage like water-snails on boats and docks and snails eat farm food.

Mollusks will take over the world!

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