Space needed for urchins?

[sacremon]

I have a 30g tank that was the sump for my 125g before I upgraded to a 300DD. I've been thinking of what I could do with it, and thought of a species tank for some urchins. In particular I was thinking of having two urchins, an Asthenosoma ijimai and a Toxopneustes pileolus.

Now, before anyone starts screaming about these two, particularly the latter: Yes, I am aware of how venomous they are. I have a Ph.D. in Toxicology. That is in large part why I am interested in keeping them. There are no children in the house. The cats have no interest in the tanks (other than the alpha female, who is offended that the fish do not acknowledge her alpha status). I would have a glass cover on the tank, probably weighted to make sure that nothing got in there even accidentally.

From what I have read, both of these species are largely herbivores. Would a 30g long tank that I supplemented with nori rubberbanded to rocks be sufficient for these two urchins?

 

[sacremon]

So, I guess no need to say no screaming. Oh well.

 

[the droob]

I don't know too much about the spieces you want to keep but the ones I've had in the past and the urchin I have now get by really well in small areas so long as they have food ,the urchin I have at the moment hardly moves at all he just keeps to a few rocks at one end of the tank eating what ever grows on them including pink coraline algea,he seems to like that the most but any green growth aswell. I'll try to post a pic of the one that I have

 

[the droob]

Pic of my urchin

Pic of my urchin

Here is a pic of the urchin I have ,hope this works ,I've never uploaded pics before!

 

[sacremon]

Nice looking urchin, and upload worked fine.

I have an urchin in my main tank, but I have no doubt that 300g is more than enough room for a single urchin (Echinometra viridis in this case). I don't want either of the urchins that I listed in my original post in the tank as they are so venomous, they would pose a deadly hazard to the fish.

There are couple other resources that I can try. Thanks for the response.