Check out the many species of Mantis Shrimp.
These shrimp are not easily available and came from several sources years ago.
They are the most common species that hitchhikes in on live rock. They change color depending on environment, and can range from bright green to brown to maroon. They only grow to about 3″, and are relatively peaceful for a mantis. They can’t hit hard enough to break thick-shelled snails or hermits. They are also more active than the chiragra species, and are often out exploring the tank. She loves to eat krill from a bamboo skewer.
This is Odontodactylus havanensis. They are fairly common off the coast of Florida and in the Caribbean. They are in the same family as the peacock mantis, but these only get about 2.5-3″. They are one of the more peaceful species, but they like to snack on small hermit crabs. They are definitely the “cutest” mantids with huge buggy eyes. They come from deeper water than most other mantids, 60-100 feet down. These are my most active mantids, and the species I have the most of ( I ordered 3 online and the guy sent 8 of them). They come out and beg for food whenever I am in the room, and they will attack a bamboo skewer even if there is no food on it. My smallest one is only 1/2″ long, and it is a struggle for her even to tackle an adult brine shrimp. The tiny one has taken up residence in an abandoned shell from a small hermit, and uses it as her burrow.
Here is another spearer, Pseudosqilla ciliata, which is a spearer that evolved into a smasher, then back into a spearer. They have the aggressive attitude of a smasher, but are relatively reef-safe (except for fish). They burrow in fine sand, and are out hunting most of the time. They will spend hours stalking small fish. They also change color depending on environment, from yellow to green, green with white stripes, and even black.
Lysiosquillina maculata are a bit different than the other mantids. Instead of “smashing” type arms, they are spearers, with arms like a praying mantis. They eat fish and shrimp. They come from the south Pacific, and make deep burrows in fine sand. They are the largest mantis shrimp, reaching over 16″ and living over 30 years. They live in monogamous pairs, with the male doing most of the hunting. They are another species that almost never leaves its burrow. This species is very uncommon, but I was lucky enough to find a pair. The ones I have are very young and small (for this species, anyway), with the male at about 5″ and the female at 6″ . I have set up a special tank for them with a cut-away burrow so I can watch their behavior.