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What is a Crustacean? - Definition, Characteristics & Types

What is a Crustacean? - Definition, Characteristics & Types
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  • 0:01 Characteristics & Anatomy
  • 2:24 Types
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

From a crab to a barnacle, crustaceans are a diverse group of animals that inhabit much of the world. This lesson will explore what it means to be a crustacean and will also provide some example organisms.

Characteristics and Anatomy

Imagine a creature that has a skeleton on the outside of its body, that has eyes that protrude on stalks, and whose blood doesn't flow through blood vessels but, instead, pools and surrounds body tissues. What is this monstrous creature? What if I were to tell you this isn't a monster, but something you've probably seen and maybe even eaten? Yep, this strange creature is a crustacean. There are over 50,000 species of crustacean and they come in all shapes and sizes, from an ocean-dwelling crab to an immobile barnacle. But before we delve into the types of crustaceans, let's take a moment to go over the characteristics and anatomy that they share.

Crustaceans belong to the phylum Arthropoda which includes critters like ants, spiders, and centipedes. It's kind of crazy to think about how delicious crab is in the same group as a spider, but they share similar characteristics. For starters, members of this phylum don't have a backbone like you and me, so they are called invertebrates; and, as mentioned earlier, they have an external skeleton, which is referred to as an exoskeleton. They also have an open circulatory system, meaning blood doesn't travel in blood vessels but makes direct contact with tissues as it flows freely. Finally, they have jointed legs and segmented bodies. So the next time you see a crab, realize it has a lot more in common with an ant than you thought!

Arthropods make up 80% of the creatures that belong to the kingdom Animalia, so it;s a diverse group, and crustaceans have their own unique characteristics that set them apart from other arthropods. Crustaceans are made up of three body parts: the head, the thorax and the abdomen. Some species have a fused thorax and head in what is called the cephalothorax. Each of these body segments can have appendages; for example, the head has antenna and the thorax has legs.

With their skeleton on the outside of their body, their blood flowing without blood vessels, and antenna protruding from their heads, you're probably thinking crustaceans cannot get any stranger, right? But you'd be wrong. Although most reproduce sexually with separate males and females, some species of crustaceans are hermaphrodites, and most crustaceans have a larval stage where all of their appendages come out of their head. Ok, now let's take some time to investigate the different types of crustaceans.

Types

Crustaceans live in a variety of environments. Sure, you can imagine a crab sitting on the bottom of the ocean, but if you came across a pill bug you probably wouldn't scream, 'Check out that crustacean!' Pill bugs are crustaceans that live on land. There are too many groups to mention here, so let's just highlight a few, starting with copepods, which are extremely small crustaceans.

There are over 13,000 species that are considered copepods. Some inhabit freshwater, some live in saltwater, others live in moss, and some are even parasitic. The copepod's claim to fame is probably their importance in the food chain. In fact, copepods are feasted upon more than any other aquatic critter. For example, they are a favorite food of commercially important fish, like mackerel and herring, as well as seabirds and whales.

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