We all know that as humans our skeletons are made of bones that are inside of our bodies, beneath our skin, veins and muscles. This is called an endoskeleton and the majority of vertebrates have this type of skeleton.
Animals that live or partially live outside of the water need some type of skeleton in order to move and support themselves.
Here are the three types of skeletons:
- Hydrostatic skeleton
So we know what an endoskeleton is, a skeleton that’s in side your body. But what are the other two?
A hydrostatic skeleton is defined as a skeleton formed by a fluid-filled compartment within the body, called the coelom. This one is the hardest to understand and explain but an example of an animal with a hydrostatic skeleton is the common earthworm if that helps make sense of it.
An exoskeleton is an external skeleton much like the name suggests. Arthropods like crabs or lobsters are examples of animals that have exoskeletons. These external skeletons are crucial to their survival since they not only support their bodies but provide them with defense against predators. These exoskeletons do not grow with the rest of their bodies so they must shed them every so often and grow new ones.
Which brings us to the topic of this article, exoskeletons and animals that have them.
So let’s get to it.
5 types of animals with exoskeletons
Arthropods are invertebrates that make up 75% of all animals on earth, and they are mostly insects. The phylum also includes spiders, centipedes, and crustaceans. This group, arthropods, makes up the majority of animals with exoskeletons. In addition to arthropods, there are some species of mollusks that have exoskeletons and sea sponges that secrete their exoskeletons.
Examples of animals with exoskeletons:
Insects are the largest group of arthropods on the planet. They have hard exoskeletons made out of chitin which protects and supports there bodies that are comprised of the head, thorax, and abdomen.
Some species of cicada live underground for the first 2-17 years of their lives. Once out of the ground the cicada is called a nymph. The nymph quickly looks for a tree to aid in the shedding of its exoskeleton. Once they finish molting they can finally begin their adult lives, the exoskeleton stays behind attached to the tree.
There are fossils of ancient grasshoppers that date back more than 300 million years, well before dinosaurs roamed the earth. Grasshoppers have large back legs for jumping but some species also have wings and are able to fly. Like other insects, grasshoppers have a hard exoskeleton made of chitin that protects their soft insides.
Ladybugs are one of the most recognized insects due to their bright red color with black dots. These colorful wing-covers protect their delicate wings that are about 4 times the size of their bodies. A ladybug’s exoskeleton is also made of chitin and protects its insides and holds its body together similar to the way our skeletal system holds us together.
2. Spiders & arachnids
Spiders are part of a group of animals called arachnids, which also belong to the group arthropods. Other types of arachnids include ticks, mites, chiggers, and scorpions whom like spiders, all have exoskeletons.
While they are rarely fatal to humans, black widow spiders and the most venomous spiders in North America. The female black widow is usually twice the size of a male and is known for actually eating the male. This is after they have successfully mated, hence the name “black widow”. Both the male and female of this species have hard exoskeletons made of protein and chitin.
Brown recluses get their name from the fact they are very reclusive and keep to themselves, human bites are rare as their fangs are small and cannot bit through clothing. These spiders are often mistaken for other non-venomous spiders like the wolf spider. A brown recluse can easily be identified by a violin-shaped marking on the top of its shell, or exoskeleton.
the emperor scorpion is another type of arachnid with a very tough outer-shell, or exoskeleton that it uses for protection from predators in the savannas of West Africa where it lives. They can grow up 7-8 inches in length and due to the fact they have mild venom and are fairly docile, they are big in the pet trade. While their stingers look pretty intimidating, they rely more on their massive claws to kill prey. An emperor scorpion sting has been compared to a bee sting for a human, not pleasant but not terribly painful considering the size of their stinger.
Crustaceans are a group of arthropods with hard exoskeletons that mainly live in the ocean. However some are found in freshwater like the crayfish and others on land like the Coconut crab, the largest land dwelling arthropod on earth.
Lobsters have a very long life span and some species can live over 100 years, continuing to grow the whole time. During the first 5 to 7 years of life a lobster will molt its exoskeleton about 25 times. After that, an adult lobster will only molt about once every year or sometimes 2.
The coconut crab is a type of hermit crab that will actually scale coconut trees and use its massive flaws to crack them open and get to the meat inside. These crabs are not to be trifled with, their pincher can create a force of up to 740lbs of pressure… enough to snap off a human finger. Coconut crabs are known for eating their own exoskeleton after molting, which can take about a month.
Freshwater crayfish, commonly called crawdads around here, are kind of like mini-lobsters found in streams, rivers, creeks, and other fresh bodies of water. Like lobsters, they regularly have to molt their exoskeletons in order to grow. The exoskeleton itself does not grow with the crayfish, which is why they must molt. For a few days following a molt they are left with a much softer exoskeleton which makes them more vulnerable to predators.
4. Millipedes & centipedes
Both millipedes and centipedes are arthropods, and both have exoskeletons.
Millipedes vs centipedes – what’s the difference?
Many get these two species of arthropods confused, but they are actually quite different. All millipedes are non venomous while many types of centipedes are venomous with some even being deadly.
Depending on the species the actual number of legs that these creatures can have greatly varies, what always holds true though is the fact that millipedes have 2 sets of legs per body segment while centipedes only have one pair of legs per segment. With this in mind, millipedes usually end up having more legs than centipedes.
A millipede’s hard exoskeleton is it’s primary defense from predators and things that would like to make it into a meal. They are known for balling up in a coil to make themselves even less appetizing and further protect their more vulnerable underside. While millipedes are not venomous, some species may secrete a poison as a secondary defense against predators.
Like millipedes, centipedes have a hard exoskeleton. Centipedes use venom to kill all of their prey, but they typically avoid humans and don’t pose any threat to us. While their venom isn’t likely to be fatal to humans, species like the Asian Forest Centipede are highly venomous and if bitten can cause serious pain and swelling.
5. Shelled mollusks
The two types of shelled mollusks that have exoskeletons are gastropods and cephalopods. Gastropods include snails and cephalopods include clams and oysters. Both types of mollusks have hard outer shells for exoskeletons. Their shells act not only as protection from predators but their actual homes. The exoskeleton of a mollusk is made of mostly calcium, compared to the exoskeleton of an arthropod which is made of chitin.
Everything from common garden snails to giant sea snails have exoskeletons in the form of shells. Their shells typically act as their primary defense against predators as they are able to just go inside and close up, similar to the way some turtles can. Unlike crustaceans, a snail does not shed its shell nor can it crawl out of it. The shell grows along with the snail throughout its life.
Clams & oysters
Seashells are the old exoskeletons of clams, oysters, snails, and other sea creatures that live in shells. A clams exoskeleton is used much in the same way as the snails, to protect its tender insides from predators. Even though a clam or oyster’s insides may look like a pile of slime to us, they actually have a nervous system, a heart, a mouth, and a stomach.