Andrea Goodman, age 9, of Delmar, New York, for her question:
Are sea anemones and sea urchins related?
The experts in this department are called zoologists. These zoology scientists sort the animals into their proper groups and classes. They examine the inside and outside of a creature very carefully before they decide where he belongs. Chances are, he shares his group with a few first cousins and maybe a lot of distant relatives.
When the tide goes out, it may leave a wonderful zoo of small animals on the soggy, sandy beach. They are not fishes, for they do not have backbones and bony skeletons. They are not even distantly related to the fishes. What's more, they are very different from each other. Of course, there are no real live mermaids in the sea but it is fun to pretend that there might be. The sea urchin looks like a pincushion that an imaginary mermaid left left near the shore. A sea anemone looks like a pretty flower that the never never mermaid tends in her underwater garden.
Zoologists, of course, are .serious scientists who dare not believe in mermaids. But they are quite sure that sea anemones and sea urchins are definitely real live animals. They know exactly how their little bodies are made. They can describe what they do and how they make a living for themselves. Zoologists need to know all these details because one of their jobs is deciding which animals are related to each other.
Somewhere in the world, you may have a double who looks just like you. You two look alikes may be distant cousins, or you may not be related at all. However, someone who does not look a bit like you may really be a first cousin, even a brother or a sister. A flowery sea anemone does not look a bit like a pin cushion sea urchin. They do not look like relatives. But zoologists do not go by looks. They examine each animal, inside and out, and what they decided about the sea anemone and the sea urchin will not surprise you at all.
Rabbits are not related to robins, though both live on the land. Sea anemones are not related to sea urchins, though both of them are small animals of the sea. For one thing, the sea anemone has a tummy shaped like an empty bag. His body is made of tough gristle it has no crusty shell or spiky spines. The sea urchin is distantly related to the five fingered starfish. His skin is covered with crusty plates and set with movable prickles. But the most important difference is in the tummy. The sea anemone stuffs his snacks into a round sac, the sea urchin digests his food in a long, tube shaped intestine.
The sea anemone belongs in the animal class Anthozoa, a name that means flower animals. The sea urchin belongs in the class Echinoidea, a name that means spiny skin. They may be related to other classmates, but they are not related to each other.
The biggest animal group is called a phylum. And each phylum is divided into a number of smaller classes. The sea anemone shares a big phylum with 10,000 other creatures. Some of them are his cousins. And all of them have sac type tummies. The sea urchin belongs in another phylum with nearly 5,000 other spiny skinned animals. They may be shaped like saucers or domes, cucumbers or starfish. But all of them have tube shaped intestines.