I have never heard a good explanation. A few decades ago, a local at a show asked one of the premier coral classifiers in the world and his answer was something like "a lot of these were discovered and classified back when ships had sails and rivets and/or made of wood and relative term meanings have changed a lot since then."
Smooth skin acros is probably a better broad classification.
Perhaps the best know "deepwater" acro is the Tyree Purple Monster and it was supposedly collected in 2m of water. The more recent version that UC collected the UC Purple Monster was also in very shallow water - there is an article on this on ReefBuilders and they used snorkels. ...hardly deep, but totally cool.
Smooth skin acros is probably a better broad classification.
Perhaps the best know "deepwater" acro is the Tyree Purple Monster and it was supposedly collected in 2m of water. The more recent version that UC collected the UC Purple Monster was also in very shallow water - there is an article on this on ReefBuilders and they used snorkels. ...hardly deep, but totally cool.
