A rather inoffensive creature. Imagine a crustacean equivalent to a turtle.
The Horseshoe Crab's body is covered in glossy chitin. His head is triangular with no neck, thin fused flesh covering bubbly eyes. A growth of carapace forms a natural helmet for the head, shaping into a widows peak at the front and covering the entire head from behind. His body is obviously warped, looking to have been blood eagled. Where should be ribs is segmented legs, the cavity instead a gaping mouth. A curved, chitinous shell grows from the back, spreading out to cover even the legs from behind. His arms are short, each hand replaced with a small chitinous claw suited for grasping. His legs are triple-jointed, ending in long crustacean fins. Between his thighs is a set of gills and lungs, allowing for breathing in and out of water. His ass is covered by a large carapace plate, a body-length solid tail poking out from beneath.