Nematocysts or bust?

[Uzidaisies]

I’m reading some stuff and getting confused over what seems to be a contradiction. I read that cnidocytes/nematocysts are a defining characteristic of all Cnidarians, but then also that some corals like leather corals and star polyps don’t have nematocysts. So what’s the deal? Do some Cnidarians lack cnidocytes or do leathers and star polyps have cnidocytes?

 

[MnFish1]

I’m reading some stuff and getting confused over what seems to be a contradiction. I read that cnidocytes/nematocysts are a defining characteristic of all Cnidarians, but then also that some corals like leather corals and star polyps don’t have nematocysts. So what’s the deal? Do some Cnidarians lack cnidocytes or do leathers and star polyps have cnidocytes?

I believe they all have a stinging mechanism. Where did you read that they do not?

 

[Uzidaisies]

I believe they do as well. Which makes it unfortunate that the first thing that comes on Google is;

 

[MnFish1]

I believe they do as well. Which makes it unfortunate that the first thing that comes on Google is;

Yeah - I looked at several places. Everything I've read is that cnidaria all have them. But - there are lots of places that say GSP do not.

 

[Pescador]

This topic can be a bit confusing, as information we find on the subject is often not complete and various sources may use different terminology. Confounding the issue more is that many sources treat "nematocyst" and "cnidocyte" as synonyms, which they are not. Many sources define the nematocyst as the stinging cell of Cnidarians, but that is not technically correct. A nematocyst is better described as the stinging organelle inside of some cnidocytes. The Cnidocyte is the defining characteristic of Cnidarians and all Cnidarians at the very least have ancestors that had cnidocytes. (I have read in one source that some octocorals have lost them all-together, but I remain skeptical until learning more.) Each cnidocyte has an organelle called a cnidocyst that discharges when a trigger mechanism on the outside of the cnidocytes is touched. A nematocyst is one type of cnidocyst. There are 3 different types. There are college-level biology textbooks that neglect to mention this fact and simply state that Cnidocytes contain nematocysts. To be fair, the stinging nematocyst is the form that is shared by all major groups of Cnidarians, but some members of those groups have lost them. Most corals have 2 kinds of cnidocysts: nematocysts and spirocysts. Corals that don't have stinging nematocysts generally use only spirocysts which capture food by ensnaring or entangling it rather than harpooning it and injecting it with venom.