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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.
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
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
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
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.
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
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.