Species Description:
The horseshoe crab, Limulus polyphemus,
is more closely related to chelicerates such as spiders, scorpions,
ticks and mites than it is to true crabs and other crustaceans.
Horseshoe crabs are considered to be "living fossils" that
have evolved little in the past 250 million years. Limulus is
an ancient genus which has probably existed since the Silurian period
(440 to 410 million years ago), and shows little morphological change
from the now extinct genus Paleolimulus that lived about 200
million years ago. Limulus polyphemus is believed to be the
closest living relative of trilobites (Shuster 1982).
Even geleend van Smithsonian