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188

invertebrate

OLogy Series
biology
card
188

invertebrate

OLogy Series
biology

Some people may call invertebrates spineless because they lack a backbone or spine! But these amazing creatures are the most abundant animals on Earth. Some invertebrates, like squid and leeches, have soft bodies, while others, like crabs, have a hard outer shell called an exoskeleton. Invertebrates are found in every ecosystem. Some, such as sponges, jellyfish, starfish, and crabs, live in the ocean.

Swimming Without a Backbone
Dolphins, fish, sharks, and whales use their backbones, and the muscles that attach to them, to swim through the water. Marine invertebrates don't have backbones, and although plenty of them, such as blue crabs, can swim, they have developed many ways to get around. Lobsters walk along the seafloor, catching their prey with long claws. Octopuses and even scallops use jet propulsion, sucking in water and forcing it out again to propel themselves through the ocean. Sea stars (starfish) and sea urchins have tube-shaped feet that work like little plungers, attaching and releasing as they walk along the bottom. Jellyfish usually drift along with currents. Sponges and sea fans simply attach themselves to rocks and wait for food to come by.

All invertebrates are cold-blooded, which means that:

they like to live in cold climates

they are mean, cold-hearted animals

their body temperature is the same as their environment's

Are you right?

Correct!

All invertebrates are cold-blooded, which means their body temperature comes to equilibrium with, or reaches the same temperature as, their external environment.

Insects, crabs, and lobsters all belong to a group of invertebrates called:

amphibians

arthropods

arachnids

Are you right?

Correct!

All arthropods have a hard outer skin called an "exoskeleton." (The prefix "exo" means "outside" or "external.") The exoskeleton is made of a strong protein called "chitin." Arthropods are the only invertebrates to have jointed legs.

Because they don't have backbones, invertebrates can never grow to be more than a few inches long.

Fact
or
Fiction
?

Fiction

While vertebrates (animals with backbones) tend to be larger than invertebrates, there are a few exceptions.

Of all the species on Earth, 99 percent are invertebrates.

Fact
or
Fiction
?

Fact

Almost all the species on Earth are invertebrates. Over a million species of invertebrates have been identified so far. And millions more are yet to be discovered.

Characteristics: no backbone, cold-blooded
Habitat: found in all ecosystems, from the Arctic regions to the tropics
Common examples: insects, crabs, octopuses, worms, and jellyfish
Cool fact: ninety-nine percent of all animals on Earth are invertebrates

Image credits: scorpion, courtesy of California Academy of Sciences, Arie van der Meijden, garden slug, courtesy of California Academy of Sciences, William Leonard, jellyfish, courtesy of NOAA, Kip Evans.