Back To CourseLife Science: Middle School
35 chapters | 241 lessons
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Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
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.
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.
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.
Bivalves are another common type of mollusk. They include clams, scallops, oysters, and mussels. They have two hinged shells that close around the animal for protection. The two, 'bi', shells are also called valves, which is how these mollusks got their name. You find bivalves in salt water as well as fresh water. If you find a lot of bivalves on your deserted island, you'll be eating well. The edible parts of the bivalves are the large adductor muscles that are used to close the shell. Bivalves don't have heads but do have gills that they use for breathing and eating. The gills filter water from which the animal extracts oxygen and food. The muscular foot of bivalves is used to burrow the animal into the sand or as an anchor to hold the animal in place.
You'll have to be fast if you want to dine on cephalopods, which include squid and octopuses. These mollusks are named for a couple of their prominent features. The prefix 'cephalo' refers to their large heads and the suffix 'pod', refers to their foot, which has been modified into a siphon or tentacles. The speed at which a cephalopod moves is created by water that is drawn into its body and then forced out through the siphon located near the animal's mouth. The water that shoots out of the siphon propels the animal in the opposite direction. One noticeable feature of most cephalopods is the absence of an outer shell. Cephalopods, like squid and cuddle fish, have small internal shells but others, like octopuses, have no shell. Cephalopods are highly advanced mollusks, with complex nervous and sensory systems that allow them to do some neat things. For example, cephalopods can change their color or shape quickly to camouflage their bodies and evade predators. If the predator keeps coming, some cephalopods can release a dark ink into the water that creates a smoke screen, giving the cephalopod time to escape.
Let's review. Mollusks are invertebrate animals with soft bodies that are often covered in hard shells. An invertebrate is an animal without a backbone. The three main parts of a mollusk's body include a muscular foot, a visceral mass, and a mantle. The three main types of mollusks are gastropods, bivalves, and cephalopods. Gastropods, like slugs and snails, can live on land or in the water. Many gastropods have beautiful spiral shells, which make them attractive to seashell hunters. Bivalves, which include clams, scallops, oysters, and mussels, have two hinged shells that close around the animal. Most cephalopods, which include squid and octopus, do not have outer shells. Cephalopods have tentacles and propel themselves through the water by shooting water of a siphon found near their mouths. They can hide from predators by changing their color or shape or releasing ink into the water.
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Back To CourseLife Science: Middle School
35 chapters | 241 lessons