I'm going to layout what I know. As a diver, and a hobbyist. Zoa's are reef scavengers that will consume any available real-estate in your tank ( and in nature.) They thrive in the areas that most other corals would reject, making them a great tank filler. Most all Zoa form mats or colonies consisting of single polyps of the same genus. (depending on the breed) these breeds can be broken down into three categorizes. 1. not connected, solo polyps 2. stringy tissue like skin between polyps 3. very thick shared skin (matt) showing only the disc's Important note: many, protect from predators with palytoxin! a very toxic poison. Currently less then 300 Zoa's are studied and recorded, but thousands have been reported. Zoa's (Brachycnemina) have two sub orders very popular in the aquarium trade; Sphenopidae (Palythoa, Protopalythoa) and Zoanththidae ( Zoanthus). Many others exist but are codependent on sponge and are not classified or studied at this time, but are found for sale. The Family of the Zoanththidae ( Zoanthus) has proven very problematic in the industry due to its poor husbandry and propagation. ++side note++ I have had these and had very poor results, they must be spread apart and do not produce many offspring. Zoanththidae ( Zoanthus) are found world wide in Sub/tropical waters. they require intense lighting and are a tidal current polyp. if give time, strong current and intense light they can thrive in a tank. they will form thick tight groups. A good healthy colony will have every other polyp staggered above the other like a tic-tac-toe board. The internal pressure (hydraulic) of the polyp will ensure it. they should not be pressed to the substrate. this restricts growth and limits the mature size of the colony. Two rings on each polyp should be seen showing a healthy polyp. Colors of polyps will vary drastically. Sphenopidae (Palythoa, Protopalythoa) this is the Paly all for one. not many have been researched. Protopalythoa the 2nd most common in the hobby. they require bright light and shallow water to thrive (tanks are not 30 feet deep so don't worry). they are known to be very robust and hardy. unlike the Zoa's the mouth disc is larger with pointed fingers (tentacles). they differ from their sister in the genus as they do not share a body mass with any other polyp. they grow solo. I will talk about Matt and others in a later post. cheers. REF "CORAL Mag March" NOAH reef studies 1986-2006" "Fed Fish and Wildlife archives 2001 Hawaiian Reefs" "Johnston Atoll study 2009" "Midway reef CPT DOI" ++++I updated with 4 Pictures of cultivated polyps from my tanks and 1 picture of green/yellow polyps thriving in a tidal zone 38 feet deep off shore in Hawaii ( notice how bright the light is).