#me sticking all the ancients under a microscope l

[impossible-rat-babies]

yes live letter important but also. thinking about pandaemonium!

[lifesciencepotluck]

Exploding poison capsules

One of the biggest reasons why I developed a deep obsession with anemones is because of my fascination with cnidae. Cnidae are subcellular structures that can do a bunch of stuff. They can play a part in aggression, adhesion and even building tubes for burrowing anemones. Cnidae are usually secreted by the Golgi apparatus, go through some fabulous modifications before moving to the surface of tentacle (or other tissues). There are three major type of cnidae: spirocysts, ptychocysts and nematocysts. They usually have a thin hollow tube that can be discharged. Spirocysts look like little corkscrews and they help anemones to stick to things. They are also unique to Anthozoans. Ptychocysts are specific to tube anemones (which aren't technically anemones but that’s a conversation for another day) and well, they help the tube anemones make adorable tubes that help them burrow into the sand. Nematocysts are the ones that involved in storing and injecting toxins.

The mechanism injecting toxins is straight out of a Michael Bay movie. Basically, the capsule (nematocysts), swells up and explodes. The thin hollow tube is shot out like a harpoon and it injects the venom into whatever poor fool is contact with the anemone or jellyfish. The actual mechanism of cnidae discharge is still a bit hazy because this entire process happens within nano seconds. 

Step 1: Have some kind of chemical or mechanical stimulation. (AKA piss off the anemone by poking it or drastically change its environment) 

Step 2: A bunch of cations (or positively charged ions) will flood the cnidae and due to the magic of osmosis, the capsule swells up as the osmotic pressure increases.

Step 3: At some point the pressure will be too damn high and the nematocysts will burst. 

Step 4: The thin hollow tube is flung out, it penetrates the target and the venom flows through the hollow tube. Congrats you have successfully injected venom into target! Yay!

Step 5: Slaughter your foes with your exploding poison capsules.

Do you finally see why I’m obsessed with these things?  

There are other theories of how the cnidae discharges (which I will cover later on), but this a general summary of what happens. The type and distribution of cnidae is impacted by a bunch of factors such as: anemone species, prey size, salinity, types of thirsty predators the anemone has to deal with, etc. Of course, there are different types of nematocysts as well. There are two main types of nematocysts: haplonemes and heteronemes. Haplonemes have tubes and spines on nematocysts that are not divided into different parts. On the other hand, heteronemes have spines, plus there is a distal basal shaft and distal tube combo. You can identify the type of cnidae through light microscopy of tissue samples from cnidarians. Sometimes you have to look at the discharged or fired nematocysts so you can see the threads/tubes in order to differentiate between different types of cnidae.

Atrichs: Haploneme. They are usually found in catch tentacles (they are extra pair of tentacles used to fight other or even the same species of anemones). Have smooth threads without nay shafts or barbs.

Holotrichs: Haploneme. There is no distinct basal shaft but there are barbs on the threads.

Basitrichs: Heteroneme. They have threads without shafts but they have barbs at the base only.

Microbasic b-mastigophores: Heteroneme. They have a shaft and the threads are not well distinguished from the shaft. The shaft contains barbs. 

Microbasic p-mastigophores: Heteroneme. The shaft is distinct from the base and has funnel shape when the nematocyst is unfired. Sometimes the thread is armed (hoplotelic).

Microbasic a-mastigophores: Heteroneme. The thread is smaller and only the barbed shaft is present. This shaft is three times as long as the capsule.

Macrobasic a-mastigophores are similar to microbasic amastigophors, but the shaft is more than three times as long as the capsule. In unexploded capsules the shaft forms coils. So, you need to have fired cnidae to tell the difference between microbasic and macrobasic a-mastigophores.

I wish my drawings of cnidae were this beautiful—but they aren’t.  So here you go. (Source: http://www.meghanrocktopus.com) 

Everyone knows that flow charts make evyerthing better! (This is from Shick’s A functional Biology of Sea anemones)

This is how nematocysts look like under a microscope. 

Cnidae aren't the only parts of an anemone that can contain toxins, some anemones have ectodermal and endodermal gland cells which can secrete and store toxins. Understanding the cnidae composition for each tissue for your anemone is important for venom extraction. Trust me you will need all the information you can get because venom extraction is a special kind of purgatory, which I will cover in my next post.

Citations:

Wei, N., Yap, L., Fautin, D. G., Ramos, D. A. & Tan, R. Sea anemones of Singapore: Synpeachia temasek new genus, new species, and redescription of Metapeachia tropica (Cnidaria: Actiniaria: Haloclavidae). Source Proc. Biol. Soc. Washingt. 127, 439–454

Yanagi, Kensuke & Fujii, Takuma. (2015). Redescription of the Sea Anemone Exocoelactis actinostoloides (Cnidaria: Anthozoa: Actiniaria) Based on a Topotypic Specimen Collected from Tokyo Bay, Japan. Species Diversity. 20. 209. 10.12782/sd.20.2.199.

Jouiaei, M. et al. Ancient venom systems: A review on cnidaria toxins. Toxins (Basel). 7, 2251–2271 (2015).

Shick JM (1991), A functional Biology of Sea anemones, Springer Science+ Business xMedia Dordrecht, 395 pp.