We looked at sponges, and our sponge was very tiny. I'd guess it was about 1 cm long, and irregularly shaped. We discussed the concept of symmetry, which is basically whether you can find one or more lines through the object that if you placed a mirror there the reflections would line up. The sponge was not symmetric, or asymmetric. One resource for if you want to learn about species of organisms that live in the ocean is the WoRMS, or World Register of Marine Species. Some interesting facts we learned about sponges:
- Sponges have no true tissue layers
- There are about 5,000 to 10,000 species of sponges
- They eat bacteria and plankton
- They suck water and food in through pores and then shoot it out the opening at the top
- Sponges don't really move around
- Recently, the genome of a sponge-associated bacteria that produces various potentially useful chemicals has been sequenced. Here is the article I tried to explain
Next we looked at hydras, which are in the phylum Cnidaria. That is the same phylum as jellyfish, which really should be called jellies (because they're not fish). The hydras looked like tiny strings, about 5 mm long and less than 1 mm wide, floating in liquid. We placed them on slides and looked at them under my microscope. They were like a long tube and had long, stringy tentacles on one end. Their bodies and tentacles were greenish like algae, and we decided that they probably look that way in order to blend in with algae but couldn't actually be photosynthetic because they're animals. Other facts:
- Hydras are radially symmetric
- They have a tubular body with a foot at one end and tentacles at the other
- The tentacles have specialized stinging cells that paralyze their prey
- Hydras don't have brains
- Food comes in through the top opening and waste leaves out the same opening
- They eat plankton
- When food is plentiful, they reproduce asexually by budding
- In harsh times, they reproduce sexually
- In a commentary article we looked at, we learned that studying the stinging cells of hydras has led to some interesting ideas about how sensory cells evolved (cells that sense things, such as hearing-related, sight-related, touch-related, etc.)
At our next class, we started by having a game show about sponges and hydras. It was really fun because the class was divided into two teams (called the Hydras and the Sponges), and each team really wanted to win. We used questions that the students created, and alternated players from each team. Some of the questions were harder than we thought they would be, and if a player got the question right, they could choose a spot on a tic tac toe game. The final score was Hydras 2 Sponges 0.
Next we started talking about planaria, which are tiny, free-living (not parasitic) flatworms. They were hard to dissect because they were less than 1 mm thick and maybe 3 mm long. But they were too big to look at with my microscope. So we mostly talked about the cool things about planaria, such as:
- They are bilaterally symmetric, which means you could draw a line down the middle and each side is a reflection of the other
- They have a head area that has two eyespots, but the eyespots aren't really eyes -- they just detect light
- They move using cilia, and glide along a layer of mucus (ew!)
- Planarians have a remarkable ability to regenerate body parts or even whole worms!
- They have a single opening digestive tract (food goes out the opening it came in)
- They have a tiny brain on each side of the head and nerve cords that go down the animal
- They can reproduce asexually or sexually and are hermaphrodites (have both male and female reproductive parts
- Studies have been done on memory in these worms, and there are kits you can get to train worms yourself
- Neuroscientists have been looking at planarians to learn about neuropharmacology (the study of drugs and chemicals in the nervous system)
Lastly, we discussed and dissected a mussel. We're pretty sure it was a zebra mussel, and it was tricky to cut the right muscle to get the shell to open. Compared to the other animals we had looked at before, this animal has a lot of structures and organs. Some facts we learned:
- Mussels are in the phylum Mollusca and class Bivalvia
- The shell has three layers, and the inner layer is the iridescent mother-of-pearl
- The foot is a large, muscular organ that pulls the animal around
- They eat plankton by pulling it in using a siphon
- Waste is eliminated using a different siphon, so they have a digestive tract (sortof)
- Mussels reproduce sexually, and there are males and females
- They have a basic nervous system
- They have a heart, but they don't have blood vessels
- I didn't have time to discuss the research article related to mussels, so that will be for next time
Wow! What a pair of classes! We had them back to back due to last week's class being cancelled and scheduling the make-up class for this week.
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