Horseshoe crabs occasionally come onto the Australian shore.
 Some evidence indicates that mating takes place only in the presence of the sand or mud in which the horseshoe crab's eggs were hatched; it is not known with certainty what is in the sand that the crabs can sense or how they sense it
 Horseshoe crabs are closely related to the extinct eurypterids (sea scorpions), which include some of the largest arthropods to have ever existed, and the two may be sister groups

