Mollusks: Characteristics & Types

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  • 0:01 What Is a Mollusk?
  • 0:56 Characteristics of Mollusks
  • 2:01 Types of Mollusks
  • 5:32 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Do you like to eat seafood, hunt for seashells, or learn about scary sea creatures? If so, then you'll want to learn about the different types of mollusks, which include the tasty bivalves, the cool-looking gastropods, and the weird cephalopods.

What Is a Mollusk?

Let's say that you're trying to become the youngest person to make a solo voyage across the ocean. The trip is going well until you sail into a terrible storm. Luckily, you make it to a small deserted island before the storm destroys your boat. It will be weeks before you're found, so you'll need to find a source of food, tools, and a way to entertain yourself so you don't go crazy. Fortunately, this island is filled with mollusks. What are mollusks, you ask? They are invertebrate animals with soft bodies that are often covered in hard shells. The soft bodies of common mollusks, like clams, oysters, snails, scallops, squid, and octopus, are eaten as food and that hard shells found on many mollusks have been crafted into tools, decorations, and even musical instruments for centuries.

Characteristics of Mollusks

Mollusks are invertebrates that belong to the phylum 'molluska'. Invertebrates are animals without backbones. Without a spine, it's easy to see why mollusks have soft bodies. Their bodies are made up of three main parts, including a muscular foot, a visceral mass, and a mantle. The foot is an appendage that some mollusks use for movement and others use for burrowing. The visceral mass is the inner part of the mollusk that contains their vital organs. It's surrounded by the mantle, which contains glands that secrete a substance that hardens into the animal's shell. Many mollusks prefer wet or damp environments but some live on dry land. The habitat they prefer is partly determined by the type of mollusk. There are tens of thousands of species that are divided into classes. Let's take a closer look at the characteristics of the three main types of mollusks that you might find on the island: gastropods, bivalves and cephalopods.

Types of Mollusks

When you go hunting for mollusks on your deserted island, be sure to watch your step. Gastropods, like slugs and snails, can be found on the ground and often like damp areas like below rocks or near debris. Yum. I bet you didn't think you'd be eating escargot when you got shipwrecked! Gastropods can be found in salt or fresh water. They vary in appearance, but typically have well developed heads, a muscular foot, and a spiral shaped shell. The head of the gastropod has tentacles that contain light detecting eyes. Their foot is used for crawling and leaves behind a slime trail as the animal pulls itself along the ground. That slime trail might make you lose your appetite, so if you can't stomach another land-based gastropod, you can dive into the water to find some sea-snails or slugs. The really cool seashells found along the beach are often one of the gorgeous gastropods, including the beautiful shells of the periwinkles, whelks, and conches. A conch would be a great mollusk to find. You could nourish your body by eating the invertebrate and then, with a little practice and a lot of breath, you can turn a conch shell into a horn to call for help. Large gastropod shells have been used for centuries as blowing horns.

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