GOOD MORNING #ScienceTwitter - hold on to your butts, b/c it's the best day of the year: #NationalSeaJellyDay! I did a thread for NSJD last year but that was before I understood how to construct threads so let's do it properly this year (1/24)
Starting off, let's take a look at how cool this alternation of generations in the typical scyphozoan jelly life cycle is: (2/24) 
But why scyphozoan jellyfish - what does that even mean? There are lots of critters in the Phylum Cnidaria, separated into Classes.
Anthozoa: our anemones and corals! Like this aggregating anemone (Anthopleura elegantissima), anthozoans look like upside-down jellies (3/24)
Anthozoa: our anemones and corals! Like this aggregating anemone (Anthopleura elegantissima), anthozoans look like upside-down jellies (3/24)
Then we have Polypodiozoa and Myxozoa, both classes of parasitic cnidarians that tend to rely on fishes, fish eggs, annelid worms, or bryozoans as hosts in their life cycles. Here is a free-living stolon of Polypodium hydriforme (4/24)
Next, let's look at the elusive class Staurozoa, the first class of our Medusozoa clade: the stalked jellyfish! I say elusive b/c they're so gosh-darned hard to find in the wild. I was lucky enough to see one as an undergrad @BamfieldMSC but not since (5/24)
Then we come to class Cubozoa: the box jellyfish! These jellies tend to have very small bells, long arms, and some produce a very potent venom - the box jellyfish usually comes to mind here! Stings from a few of these spp can cause incredible pain & may even lead to death (6/24)
Sidebar: bell, arms, what? Let's take a quick break from the classes to check out the anatomy of a medusa. The 'jelly' part that we're used to seeing is the bell at the top, which houses gonads, the gut, muscles, & the mouth. Arms extend from the bell, with stinging cells (7/24)
In the Hydrozoan class, there are loads of subclasses & orders, so I'll just highlight a few. First up, Siphonophorae! Critters in this order look like a single organism but are actually a colony of zooids (small, individual animals) that have their own function (8/24)
The Portuguese man-of-war (Physalia physalis) is a pretty recognizable siphonophore, Ernst Haeckel drew tons of other siphonophore body plans in Kunstformen der Natur in 1904 (9/24)
Another super neat order of the hydrozoans is the Limnomedusae! The flower hat jelly (Olindias formosus) has a translucent bell with pinstripes and eats mostly small fish (10/24)
Now, the home of my favourite hydrozoan, the order Leptothecata. This order contains the crystal jelly (Aequorea victoria). While it's not the flashiest, green fluorescent protein (GFP) was isolated from this jelly, completely revolutionizing the biomedical imaging field (11/24)
Finally, we get to the order of the "true jellyfish", Scyphozoa, which is separated into the subclasses Discomedusae and Coronatae. The Coronatae jellies (crown jellyfishes) get their shape from a deep groove running around their bell, but they also are bioluminescent! (12/24)
This Nausithoe aurea is a great example of the crown-like shape these jellies have, while this Atolla wyvillei (viewed under white light) shows just how different deep-sea jellies can look (13/24)
Last, but certainly not least, we have the Discomedusae, the subclass of "true jellies" that is likely the most familiar. These jellies are more likely to swarm or undergo population blooms, making these smacks of jellies (yes, that's the real group name!) easy to spot (14/24)
This is my favourite class but I'm biased b/c back in my days of being a jellyfish biologist, I took care of the world's largest psuedokreisel, which housed Pacific sea nettles (Chrysaora fuscescens) & as much as I loved them, their sting was less than pleasant (15/24)
Sidebar #2: the sting of jellies has come up a few times now, but what does that actually mean? Obviously, jellies aren't swimming around with wasp stingers akimbo, but they may as well be (16/24)
This graphic is a great introduction to how a cnidocyst is ejected from a cnidocyte. A mechanical stimulus (like a touch or a brush against) will trigger the cnidocil to open the operculum (the door keeping the coil inside), which lets the harpoon-like cnidocyst shoot out (17/24)
But there are a lot of different terms that describe the stinging nature of the cells, so here's a handy comparison table of the differences b/w cnidocytes and nematocysts (18/24)
Sidebar personal anecdote: I was once stung by a nudibranch that had sequestered the cnida of a lion's mane jellyfish (Cyanea capillata) & it was so painful and swollen that I brought the nudi back to @SuzAnthony @BamfieldMSC to see what the heck was going on (19/24)
@SuzAnthony was researching that spp of nudibranch & she imaged all the stinging cells on a DIC scope for us to check out. Look at how cool these cells look up close! (20/24)
Jellyfish are found nearly everywhere, in both marine & freshwater (see map by Brotz et al. 2012), & are doing some pretty interesting things as our world changes around them. Despite being 'unchanged' for more than 500 million years, these creatures have persisted (21/24)
And one last sidebar: the immortal jellyfish can go from polyp to medusa and then *back to a polyp* if the conditions are unfavourable. How wild is that?! Below are Turritopsis dohrnii and T. nutricula (22/24)
Jellyfish aren't just beautiful to watch, they are incredible, interesting creatures & we have so much more to learn about them. So if you are in love with jellies after this, follow @baileys & @RebeccaRHelm for #DailyJelly updates & fun facts. Happy #NationalJellyDay 💙 (23/24)
Also, follow @jellywatch (for jellies) @beroe (for deep-sea gelatinous zooplankton), @DaviesswPhD @DanielWuitchik @HAichelman @NicolaKriefall @hrivera28 @thedavieslab (for corals) & @Jason_Macrander (for anemones) (24/24)
