INVERTEBRATES ONE OF TWO MAJOR ANIMAL GROUPINGS
There are two basic groups of higher animals. They are vertebrates and invertebrates.
While both have advanced through the processes of evolution, there is one fundamental
difference. Invertebrates do not have backbones. Both groups are in the Kingdom
Animalia, but their bodies are organized differently. What makes invertebrates different?
All invertebrates share common traits. At the bottom of the invertebrate world are the
sponges. Sometimes they don't fit in but they are still part of the group. Here's the nice
and neat little list.
(1) They are multicellular. It's more than being a colony of individual cells. The cells
are working together for the survival of the organism. All of the cells have specific duties
and responsibilities.
(2) No backbone. We already talked about this one. That's the whole definition of
invertebrate, no vertebrae.
(3) No cell walls. When we talked about plants, we always mentioned cell walls.
Invertebrates don't have them. Remember that even if none of them look like animals,
they are. Being an animal means you have no cell wall.
(4) Here are a few that have the qualifier "most" attached. That means not all of them
have the trait, but most do. Most of them have tissues (not sponges) that are specific
organizations of cells. Most of them reproduce sexually (not asexually). That means two
gametes combine to form a new organism. Those gametes come from separate
organisms (male and female).
Most invertebrates can move. Even sponges move when they are very young and very
small. Once they settle down they don't move anymore. Other invertebrates like lobsters
and insects move around their whole lives. Most invertebrates are organized in a way
called symmetrical. Symmetrical organization means when you can draw a line down
the middle of the organism and the two sides look like mirror images. Draw a line down
the middle of yourself and one side looks like the other side. If you draw a line down the
middle of an octopus you would find two sides with equal parts. Remember we said
most? Sponges and some coral are not symmetrical.
(5) Invertebrates can't make their own food. Scientists use the word heterotrophic.
Heterotrophs feed off other things to get their energy. Plants are autotrophic. They
make their own food. Being heterotrophic is one of the main characteristics of being an
animal. We eat things, whether it is plants or other animals. That's just the way the
world works.
VERTEBRATE BASICS
Vertebrates are the most advanced organisms on Earth. The traits that make all of the
animals in this section special are their spinal cords, vertebrae, and notochords. It's
all about having a series of nerves along your back (dorsal side). If you are an organism,
you can't just have the nerves sitting there. You need to give those nerves support and
protection. That need brings us to the backbones and a rod of cartilage called the
notochord.
NOT SO MANY SPECIES
Fifty thousand species might seem like a lot. Compared to the invertebrates, there are
not that many species of vertebrates. You might be asking why. One reason is that
vertebrates are usually larger than invertebrates. They need more space. Another
reason is that, even though they are more advanced, there are many limitations on the
environments that are available to them.
Think about it this way. If you are smart mammal, would you rather live near the ocean
or in the frozen tundra of the arctic? Many land animals can make that decision and
move to more desirable areas for living. Those nicer areas can only support so many
species of animals.
THEY'VE GOT THE BRAINS
Vertebrates are smart. Some of them are very smart. We mean you. Most vertebrates
have very advanced nervous systems. While a goldfish might not compare to your
intelligence, when you compare a goldfish to a sea anemone, a goldfish is like Einstein.
Octopi are probably the smartest invertebrates and may equal or be smarter than some
vertebrates. Octopi are the exception in the invertebrate category.
More cool traits about vertebrates are that they have muscles and skeletons. While the
materials may vary, muscles allow vertebrates to move around very efficiently and
perform complex moves. That ability to move and the intelligence to go with it gives
vertebrates such as reptiles and birds an advantage in the natural world.