Small (under 2.5 inches), cavity living gonodactyllids, haptosquillids and chorisquillids will do fine in a 2.5 gal system as long as there is good flow and water treatement. The footprint of the tank really isn't that important to the animal. It spends most of its time in the cavity and will do well in a 3-D world. The only time I would worry about the amount of sand or gravel area is if I had a burrowing species such as odontodactylids, lysiosquillids or Pseudosquilla ciliata..
There really are no consistant common names that can be used for mantis shrimp other than "Peacock" and "Clown" that are associated with Odontodactylus scyllarus. Occasionally you will see "striped" or "zebra" used to described a lysiosquillid and "rainbow" for Pseudosquilla ciliata.
Roy
