The division of the Crustaceans into groups of aggressive and passive species is based on extensive experience on the behavior of different species. As a general rule most shrimps are passive (mantis shrimps being a notable exception), while lobsters and crabs are a bit more aggressive. 

Technically, both groups are equally aggressive, it is just that the crabs and lobsters are better equipped with larger claws to do more damage quicker. These aggressive specimens may attack other crustaceans, small fish, and other small invertebrates. Avoid exceptionally large specimens, and watch closely for the first few days for signs of injury. 

All crustaceans will do well on a variety of high protein foods such as frozen shrimp and squid. Many of these animals run the risk of nipping cniderians. The following list will cover some of the specific concerns of the different genera. 

Panulirus- The Spiny Lobsters. They are not too aggressive, and will only attack very small (about 1/5 their size) animals so most larger organisms are safe. They can eat sessile organisms such as barnacles, and clams. Provide them with a small chunk of food every 2-3 days. If a small cave is provided for them, they will quickly adopt it as a home. 

Enoplometopus- The Reef Lobsters. Their large claws are for defense and are not often used in gathering food. None the less, they can capture and eat small animals. Sessile (permanently attached animals) are not at any risk unless the animal is very hungry. They will eat chunks of frozen foods, and are best observed at either dawn or dusk. 

Stenorhynchus- These are the bizarre Arrow Crabs. They are comparatively fragile and will not bother anything too big or fast . Small sessile invertebrates and small shrimps may be attacked, however this is uncommon. If fed well on standard crab fare, they are quite passive. 

Dardanus- The comical Hermit Crabs. These animals have strong claws that enable them to make a meal of many slow moving or sessile animals. The do best as a janitor in a tank of larger fishes and hardy larger invertebrates. Hermits can crawl out of a tank by shimmying up the airline, so secure the aquarium! 

Squilla- The infamous Mantis Shrimps. They possess claws so powerful that some species can crush your finger with a single blow! A curiosity best placed into an aquarium designed just for them. They need some sand to dig in and rocks to hide among. Almost any food is greedy consumed, and only sessile invertebrates may escape these incredibly voracious animals. 

Neopetrolisthes- The unique anemone crabs. They are harmless, and need an anemone to hide among to avoid being attacked. Liquid invertebrate foods are sufficient and the crab attains the food by filtering the water using their specially modified claws. 

There are many other species of crustaceans that you might come across. Take a good look at their pinchers and size, and this will give you some idea as to their ability to do harm. Consult your fish person for any other information regarding your specific "decapod friends".