When poking a Elder Guardian with a mob prism it always says Woot:none:Guardian and when placed in a factory only produces the normal Guardian drops.

I'd love to be able to farm them sponges from the Elder Guardians too ;)

Didn't even know the Elder Guardian existed!
From the code it should be trivial to add support to identify it correctly.

Code added.
Elder Guardians are now generating (with looting III)
Prismarine Shards
Fish (!)
Sponge
Prismarine Crytstals

Awesome thanks a bunch ;)