Invertebrates. When Carl Linnaeus first created his method for organizing animals, he had just two families of invertebrates: Insecta (insects) and Vermes (worms).
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When Carl Linnaeus first created his method for organizing animals, he had just two families of invertebrates:
Insecta (insects) and Vermes (worms).
Since that time, scientists have found more invertebrates and have created more classifications. We will talk about six main categories or families of invertebrates.
The “kitchen sponge”
The main member of the Porifera family is the sponge. That doesn’t mean it is a small family. There are several thousand different kinds of sponges.
Sponges are a very simple animal. They have no brain, internal organs, blood, eyes, or ears. They do not have nervous, digestive or circulatory systems.
Sponges rely on having water constantly flow through their bodies to obtain food and oxygen and to remove wastes from their bodies. They attach themselves to the bottom of the ocean or to the sides of underwater mountains. Water is continually passing over them, going through pores and making it possible for them to filter food particles from the water. Sponges are nature’s natural water filter!
Click on the “glass sponge” to view scientists going down the Cayman wall to view sponges in the ocean.
The next invertebrate group we will look at is the Cnidarians family (pronounced: nie-dare-ee-uns Note: the initial ‘c’ is silent). This family has two groups. One contains the anemones and corals (classified as “Anthozoa” - the name comes from the Greek words ánthos – “flower” and zóa - "animals", hence anthozoa = "flower animals,“ which fits them well because of their flower-like appearance.)
The cnidarians group contains over 10,000 species of animals.
Their bodies are made of a non-living jelly-like substance. They have muscles, nervous systems, and some have sensory organs.
Cnidarians are distinguished from all other animals by having special cells containing toxins that fire like harpoons and are used mainly to capture prey. That’s why you can get quite a sting from jellyfish. The “stingers” on jellyfish hang down, and the “stingers” on anemones stick up.
Most cnidarians prey on organisms ranging in size from microscopic organisms called plankton to animals several times larger than themselves. Many feed on algae and parasites.
These animals have to watch out because there are other animals that like to eat them: starfish, sea slugs, fish, and turtles like to eat coral, anemones, and jelly fish.
Click on the jellyfish below to see a short clip about jellyfish from National Geographic:
A third group of invertebrates is the Echinoderms (pronounced: ee-kine-oa-derms ). The word “echinoderm” means “spiny skinned.” Many echinoderms are covered with spines.Most adults are easy to recognize because of their five-point, radial symmetry, which means many Echinoderms look the same on both sides when cut in half.
This class includes familiar animals like sea stars, sea urchins, sand dollars, and sea cucumbers.
because they have appendages or
patterns in their bodies in multiples of five.
Echinoderms are a little more sophisticated than Cnidarians as they have a digestive system.
Many have a skeleton on the inside of their bodies, but no backbone.
One of the most notable characteristics of echinoderms is their ability to regenerate tissue, organs, limbs. For example, if a starfish loses a leg, it can grow a new one! In some cases, they can completely regenerate from a single limb.
These colorful animals have defense mechanisms to help protect them from predators; some have spines, and others possess toxins in their bodies that hurt a predator when they bite them or that can be sent out through their tube-like feet.
Crabs, sharks, otters, and sea birds
like to eat echinoderms. In addition
to being food for larger animals,
they also provide habitats for
parasites, including crabs, worms,
Echinoderms also help build land. Their bone-like skeletons are major contributors to many limestone formations throughout the world.
Snails, slugs, clams, oysters, octopus, and squid are all part of the next group of invertebrates we will look at. What is similar about the bodies of these animals?
The Mollusca family (pronounced: mul-us-ku), commonly known as “mollusks,” are a group of invertebrates that have soft bodies. There are a variety of members of the mollusca family, some with hard shells that provide protection, and others that do not have a hard shell to protect their soft bodies.
Mollusks have more highly-developed
body systems than the other invertebrates
we have looked at so far. In fact, the
squid and octopus have very sophisticated
Besides being “smart,” the giant squid and the colossal squid are also the largest animals of all the invertebrate families. A colossal squid was discovered that was 10 meters (33 ft) long and weighed 500 kilograms (1,100 lb)!
This picture gives
you an idea of how
large that squid
would look along
side an adult
Have you been to a beach? You have probably found the remains of many mollusks:
Mollusks have been an
important food source for
humans for hundreds of years.
Other animals eat them,
Additional uses of mollusks by
humans include using the
shells to trade as a form of
currency, harvesting pearls
from oysters and mussels, and even the production of a special dye called “Tyrian purple” used to dye royal robes back before the time of Christ.
Worms are the fifth class of invertebrates we’ll talk about. Worms have long, tube-like bodies and no legs.Worms can be microscopic (very small!); they can also be as long as a meter stick!They live in various places—oceans,fresh water, on land, on plants, andeven in animals. Where have you seen worms?
The last class of invertebrates we will talk about are the Arthropods (pronounced: ar-throw-pods). This is the largest group of invertebrates, and you see members of this family nearly every day. Arachnids (spiders and scorpions), insects, and crustaceans are all part of this family.
The main characteristics of this family is that they generally have exoskeletons (skeletons on the outside of their bodies), jointed legs, and segmented bodies. Have you ever seen a crab? Crabs have a hard shell on the outside. This exoskeleton protects the soft insides of their bodies. Can you think of any insects that have hard coverings on the outside of their bodies?
Look closely at the legs of this ant. Can you see how they have several places where the legs bend? They have six jointed legs. And what do you notice about the shape of its body?
These six families make up a majority of the invertebrates in the world, though there are additional families we could study, also.
The invertebrate family contains some unique and exciting animals! Be on the lookout for invertebrates this week – you should find quite a few. Remember, they outnumber vertebrates, including us, 9 to 1!