Lesson 11 of Apologia's Exploring Creation with Zoology 2: Swimming Creatures of the Fifth Day is all about "Echinoderms," meaning, "spiny skin." This includes sea stars, brittle stars, crinoids, sea urchins, sand dollars, and sea cucumbers.
As with every lesson in this study, we pair the text with the Junior Zoology 2 Notebooking Journal, also from Apologia.
We learned that echinoderms have no eyes, no brain, and tube feet for suctioning onto surfaces, breathing, and tasting! These critters are fascinating!
The first one we focused on was sea stars, like Patrick here, from Spongebob.
I have two samples in our collection of sea items so we decided to investigate them.
Taking a closer look at those tube feet!
Like most sea stars, this one has five rays extending from its central disk. That is where the animal's mouth is located. Though you would think it would pull things into the mouth, it doesn't. It actually ejects its stomach from the mouth to eat its prey! Then, after it's done, it pulls its stomach back inside itself to complete the digestion process. Who knew?!
Looking for our other sample's mouth ...
You can also see the tube feet in the center of each ray.
Everything we learn is recorded in our journal.
As you may already know, sea stars, like many sea creatures, are able to regenerate parts of their bodies. However, many years ago, this was not yet known. Sea stars love to eat clams and long ago, clam fishermen considered the sea stars a nuisance. To try to eliminate them, when they were caught in nets, the fishermen would cut them in half and throw them back into the sea, thinking they were killing the sea stars. Not so. Even though they were trying to reduce the sea star population, they were, in fact, increasing the numbers of sea stars because the animals were regenerating themselves! Instead of one dead sea star, the fishermen ensured two living ones! Maggie thought this was hilarious so I challenged her to tell the story in a comic strip.
That's one angry fisherman!
I love kids' drawings!
"POP!" So cute! Dumb ol' fisherman!
We continued our reading in our text to learn about brittle stars, crinoids, sea urchins, sand dollars, and sea cucumbers. It was interesting to learn that brittle stars are not actually brittle, though. They are thought to be fragile, but if threatened, they willingly drop their own arms to escape.
Living sand dollars look quite different from the white sand dollar tests you think of when you think of these creatures. When alive, their entire bodies are covered with tiny spines. Below is a picture we found on an image search.
I had a sand dollar test in my stash so we observed it, too.
The flower shape on the test is where its tube feet stuck out.
In the center of the underside, you can see where its mouth is located. The grooves leading to the mouth are called food grooves. Tiny hairs (cilia) help the spines move food into these food grooves, where they travel down to the mouth. It's like it's got its own food delivery system!
We love this curriculum!
For fun, we followed the instructions in the text to make our own "Salty Brittle Star." Maggie wanted a red star, so we added red food coloring to our just boiled water.
Here, she is mixing the food coloring in, as well as starting to add a lot of salt.
We kept adding salt and stirring until the salt seemed to no longer dissolve in the hot water. This meant we had a "saturated" saltwater solution.
Next, we tied together five pieces of cotton string to resemble the shape of a brittle star. We poured our saturated saltwater solution into our measuring cup and then taped the ends of our "star" in place, so that a large part of it was submerged.
Then it was time to wait.
This is what our measuring cup looked like after 4 days! Wild!
Ready to come out, brittle star?
We laid it on paper towels to dry.
We are currently also doing a geology course, so we were intrigued by the cubical crystals the salt formed.
Once dry, we had our "Salty Brittle Star!"
Finally, it was time to add some echinoderms to our ocean box. Maggie decided toothpicks in clay would make a good urchin.
Our sea star!
Daddy helped, too. He made an urchin with clay spines. Snazzy!
Once they dried, in the box they went! Only two more lessons and our ocean box will be complete!
Next up? Cnidarians! Stay tuned!