Biology Lab: Sponges, Jellies, Flatworms & Molluscs

We did a super cool lab this week – and a relatively photogenic one, at that – so I thought I’d post a few photos! We had a bunch of live specimens (mostly marine inverts from Bodega Bay), and we did our first dissection of the semester – a squid. SUPER COOL!

Here’s a planaria, a type of flatworm (phylum Platyhelminthes). SO CUTE!


Planaria are non-parasitic, and can regenerate themselves – maybe in elementary school you did the experiment where you cut their head in half, bilaterally, and each half will grow back into a complete head? Yeah. That’s these guys. (We didn’t do that experiment, though; just looked at them through the dissecting scope). ALSO how hard does this photo rock, considering I took it through the microscope with my iPhone?

Next, we have a chiton (phylum Mollusca) … that’s the chiton in the center, holding on to some other kind of large, empty shell.


Here’s that same chiton inside the tank, giving us a lovely view of it’s mouth (to the far left), and its gills (which are inside that crevice that goes all the way around the body – you can see them nicely in that part at the upper left that is exposed.


There are also some anemones in this photo – phylum Cnidaria (closely related to jellyfish). I tried to get some individual pictures, but they came out crappy. They’re super pretty, though.

And here’s a nudibranch, or sea slug. Also a mollusk. And very, very pretty. (Again, not a great photo). Like I said, all these things came from Bodega Bay, and are relatively easy to find at low tide.


And now for the fun part … SQUID DISSECTION!

Okay, let’s start with a dorsal view of the squid:


There are two fins at the top (anterior) end, and ten appendages at the posterior end (two long “tentacles,” and eight shorter “arms”). You can also see the eyes (right above the arms), and all the spots on the body are called chromatophores – pigmented organs that allow the squid to change colors.

Here, I’ve flipped my squid onto its back, revealing the ventral view, and put my probe through the siphon, or funnel. This is the all-purpose orifice through which waste products, ink, and reproduction takes place. You also have a better view of the arms and tentacles, include the little suction cups:


One of the eyes:


I’ve pulled back the arms to reveal the mouth, which contains a hard and very sharp beak:


More magnificent iPhone scope photography haha; this is the beak magnified under the dissecting scope. ISN’T THAT COOL? It looks like something I’d expect to see on a parrot. Or a dinosaur. 😀 Super sharp:


The dissection (other than the removal of the beak) consists of one single cut: a slit up the middle of the ventral side of the mantle (the sheath that covers the organs). We then pin back the mantle to reveal the organs. (BTW, this is a different squid; the full-body pics of my squid were blurry):


Let’s look a bit closer. Here, I’ve pushed aside some of the organs to revel the “pen” – those straight structures just to the right of center in the photo. The pen is rigid, and made of chitin – the same stuff that makes up the shell of a snail:


Okay, different squid again. This one is male; I’m pretty sure the little oval-shaped organ at the center of the photo is the testis, where sperm is produced. We can also see the ink sac in this photo – the gray and black organ that runs down the middle in the right half of the photo. There wasn’t a lot of ink in this one, but sometimes there is. I have students write their initials with it. 😀 This is also a good time to point out the gills – they’re the two sort of curved structures right near the pins, on the top and bottom.


And yet another squid! This one is female. The large, smooth white structure just above the center of the photo is the nidamental gland, which is part of reproduction, and below that, the clear organ in the bottom right is the ovary. You can even see some eggs:


OKAY! There are other organs it’s possible to see, but it’s tricky to describe that without sticking arrows everywhere. If you’d like a somewhat more thorough “tour,” this is nice dissection video.

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