Indo-Pacific Horseshoe Crab (Tachypleus gigas), family Limulidae, order Xiphosura, Odisha, India

Horseshoe Crabs (Limulidae) have been around relatively unchanged since at least the early Triassic period, 250 million years ago.

They live in the ocean but return to land to lay eggs

They are not crabs, but are most closely related to Arachnids.

There are 4 living species, 3 in South and Southeast Asia and 1 in Eastern North America

Horseshoe crabs:  Limulus polyphemus, Tachypleus tridentatus

eggs

Cancer of Moluccas (Crabs of the Moluccan [Spice] Islands) - in August Basilius and Michael Rupertus Fasciculus rariorum Book (Petrus Iselburg drew them alive) - 1616 - in Herzog August Library in Wolfenbüttel, Germany  

Selected Delights of Nature from Natural History Cabinet - Georg Wolfgang Knorr - 1766-1767

Recherches sur l'anatomie des Limules (Horseshoe Crab Anatomy Research) - Paris - 1873

Tachypleus tridentatus - Fauna japonica - vol.1 - 1833

The Horseshoe crab - Limulus polyphemus from the John Reeves Collection

horseshoe crab anatomy - nervous system

Ernst Haeckel - Athropods - from Kunstformen der Natur (Art Forms of Nature) published in 1904

Charlie’s Horseshoe Crab costume - 2018 Halloween Costume Contest - Kimberly, the 'Horseshoe Crab' costume creator writes: Charlie, 4 years old, loves ocean animals and decided she wanted to be a horseshoe crab for Halloween. Her Dad made the costume using EVA foam exercise mats (using a heat gun to mold/sculpt the right shape), contact cement, and a Plasti-dip base coast with a spray paint finish. Spandex was used for the joints between the segments, so she can get around pretty well. The costume is put on using a handmade vest with Velcro straps for easy on and off.