Present on the Earth's surface for hundreds of millions of years, as evidenced by fossils, the atlantic horseshoe crab is among the oldest species still alive today ! Directly from prehistoric times, its morphology has remained unchanged, making the atlantic horseshoe crab a living fossil and a testament to the past. The atlantic horseshoe crab is essentially a prehistoric crab and like crabs belongs to the phylum Arthropoda.

At first glance, the atlantic horseshoe crab's smooth appearance, color and shape resemble a heavy metallic soldier's helmet. But a closer look reveals a distinctive shape in its front carapace which gives it the english name « horseshoe crab ».

Its body is covered by a carapace made up of two distinct, articulated parts, extended by a spine.

On the head, two small eyes emerge on the smooth surface of the largest carapace. The rear carapace is narrower and bordered by numerous movable spines on either side.

The atlantic horseshoe crab is bluish-gray and averages about 20 inches in length for females. Males are smaller.

The species Limulus polyphemus is the most common horseshoe crab species. This species is found along the western Atlantic coast from Nova Scotia in the north to Florida in the south and along the Gulf of Mexico.

If you visit Florida, check out the Ding Darling Wildlife Refuge on Sanibel Island near Fort Myers, where you might see atlantic horseshoe crabs along the shoreline !

Atlantic horseshoe crabs inhabit shallow waters along the coasts on sandy or even muddy bottoms.

They primarily feed on small invertebrates found by digging through sand or mud.

In spring, atlantic horseshoe crabs move closer to shore to breed, and large gatherings can be observed. The male mates with the female, who then deposits fertilized eggs in a nest dug into the sand. The eggs hatch about a month later.

A remnant of the past, horseshoe crabs today are represented by four known species. As mentioned, the first species Limulus polyphemus lives along the western Atlantic coast and in the Gulf of Mexico. The other three species - Carcinoscorpius rotundicauda, Tachypleus gigas and Tachypleus tridentatus - are found along the coasts of southeast Asia. All four species share similar characteristics.

Unlike most living species, the horseshoe crab has blue blood. While red blood color is due to the presence of hemoglobin, blue blood results from hemocyanin, a protein that like hemoglobin transports oxygen but contains copper instead of iron.

The horseshoe crab's blue blood is highly sought after in the medical and pharmaceutical fields for its clotting properties when exposed to bacteria.

You can observe atlantic horseshoe crabs in shallow waters along mangrove-lined shores.