Zoanthid

Got the idea from https://www.thingiverse.com/thing:4653240 , but made this one from scratch since that one was broken. The plugs from that one will also work on this.
The top should fit onto the bottom somewhat snug, but I'd still recommend that you superglue them together.
I also made a mushroom cage attachment that goes on top snugly. Mine fits just barely around my plugs, but you may need to glue tiny pieces of filament near the base to the cage where there are gaps so it doesn't go all the way down on it.
The frag plugs I used are the Ocean Wonders 3/4" Crown | 7/16" Base plugs.
(https://www.bulkreefsupply.com/bright-white-ceramic-coral-frag-plugs-oceans-wonders.html)
I printed everything at 110% with these plugs and it fits perfectly.
The bottom plug portion can also be used at giant frag plugs.