Box crabsof the family Calappidae are characterised by possessing dimorphic chelae - one has a special tooth for "cutting" open shells (gastropods), the other with long slender fingers to pull out the exposed gastropod. Interestingly, the cutting chela is almost always right-handed. The reason is simple - the right-handed cutter works best when the shell has the opening (the aperture) on the right as well. This situation is like the problem faced by left handed people who have to use tools (like can-openers) designed for right-handed people. Left-handed people have a terrible time usingnormal can-openers. In the sea, hunters (crabs) and hunted (gastropod shells) are engaged in an arms race! The shells have the opening on the right side, and the crabs have evolved the appropriate weapon to deal with it! Remarkably, this connection was only discovered in 1984! The SANTO 2006 expedition has so far found five species of box crabs!

Calappa bicornis - a large box crab from medium depths