Underside of Female Horseshoe Crab
This is a picture of the underside of a female horseshoe crab. The way to identify a female is that the first four sets of appendages are identical with the exception of size.
This photo also gives a pretty good view of the mouth. Horseshoe crabs do not have a jaw, so they can not bite. They push the food into their mouth with two small appendages and then grind up the food with coarse hair like shoulders.