Arthropod Types: Crustacea, Chelicerata & Uniramia

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  • 0:01 Arthropods Are Everywhere
  • 0:46 Crustaceans
  • 1:53 Chelicerates
  • 2:59 Uniramians
  • 4:13 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Spiders, ticks, and crabs, oh my! This lesson will discuss the arthropods, which includes all of your favorite creepy-crawly creatures, as well as some that you may not have even known belong to this group.

Arthropods Are Everywhere

I don't want to scare you, but right now you're surrounded! That's right, there are arthropods just about everywhere you look. These are segmented animals with an exoskeleton and jointed appendages. And it shouldn't be surprising that we encounter them so frequently, given that there are over a million known species of arthropods on Earth! These include things like insects, spiders, crabs, lobsters, mites (like ticks), and a whole host of other animals.

The phylum Arthropoda is incredibly diverse, so we have a few sub-phyla to better group them. Let's go through these groupings to understand what makes them special: sub-phylum Crustacea, sub-phylum Chelicerata, and sub-phylum Uniramia. Ready to get started?


Not all crustaceans are aquatic, but if you want to find one, your best bet is to look in the water, and especially marine waters. Crabs, crayfish, lobster, shrimps, and barnacles are all a part of this group. But with over 40,000 different species, the list doesn't stop there! Water fleas, krill, and small copepods also make up this large and diverse sub-phylum.

Crustaceans are very special, too, because their exoskeleton is different than that of other arthropods. In general, exoskeletons are somewhat rigid and therefore provide their owner with protection like body armor would. But with crustaceans, their exoskeletons also have calcium carbonate in them, making them even more rigid and protective. Have you ever tried to crack open a crab or a lobster with your bare hands? It's not easy!

As you can imagine, crustaceans come in all shapes and sizes. Some are predators, others are scavengers, and others still are filter feeders. They have very complicated mouth parts, and many of the mobile crustaceans have swimmerets, or small swimming legs, that help them move through the water, among other things.


The word chelicerate may not roll off the tongue, nor does it necessarily ring a bell when you hear it. But, I guarantee you've heard of these guys before, and with over 100,000 species, I'd be pretty surprised if you hadn't! In this group you'll mostly find warm and dry land dwellers such as spiders, scorpions, ticks, and mites. Horseshoe crabs are also in this group and, amazingly, they have not only changed very little over hundreds of millions of years, but are also the only remaining marine chelicerates.

The animals that make up Chelicerata are incredible and unique. Some, like scorpions and spiders, have poison that can be used to kill their prey. Spiders are also able to spin webs, which can be used for movement as well as catching food for dinner. And though you can't see them, thousands of dust mites can live quite happily in just a few square centimeters of your carpet or rug.

The main difference that you'll notice with the bodies of chelicerates is that they have only two segments instead of three. In addition to their abdomen, their head and thorax are fused together into one segment called a cephalothorax.

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