The animals within this topic are technically divided into two Infraorders. Hermit Crabs, Porcelin Crabs, and crabs that look like lobsters, but are really crabs and are called Squat Lobsters are in the Anomura Infraorder. Those in the Infraorder Brachyura contain what is called 'True Crabs.' The main different is that those called true crabs possess flattened bodies, an abdomen located on their bottom side, and short antennae. In other words - they look like a true crab! Of the True Crabs, only a few are seen in the trade, as most are either too large or too aggressive, but many will be discussed here and/or shown for identification purposes.
FYI - Catching unwanted crabs is a question I’ve fielded numerous times. The best way to rid unwanted specimens comes with using a large tall glass, similar to a drinking water glass. Simply bait the glass with a tasty morsel and place the upright glass at the aquarium bottom touching some rock in the evening. The crab will sense the food and using the rock surface, gain entrance to the glass. Because the glass has smooth sides, it won’t be able to climb out. Not always 100% effective, but has resolved some terrible crab problems.
To make viewing or locating the subject crabs of interest fairly easy I've formed the following groups: Hermit Crabs; Porcelain Crabs; Squat Lobsters; Algae Consuming Crabs; Spider/Arrow Crabs, Decorator/Partner Crabs (lives on or with other sea creatures); Horseshoe Crab and finally some odd crab-like creatures called 'sea-spiders.'