Horseshoe crabs absorb oxygen from the water using gills, each containing about 150 leaf-like membranes (lamellae). The grills are located under the abdomen.
used to be my pet...
In all seriousness though. The last photo makes me sick.
incorrect. horseshoe crabs are not crustaceans at all and in fact are more closely related to mites, spiders, scorpions, etc.