[5] Horseshoe crabs are commonly known by biologists around the world as a living fossil because they have remained practically unchanged in terms of shape and size for millions of years.

Although their physiology has changed over the years, their typical three piece exoskeleton, consisting of a prosoma, opisthosoma, and telson, has remained since the mid-Paleozoic era.

[6] Fossils of horseshoe crabs that have been dated to over 400 million years ago look almost identical to those species that are still alive today.

[8][6] The basic body plan of a horseshoe crab consists of three parts: the prosoma, the opisthosoma and the tail (telson).

[5][10] Most of the appendages have straight, scissor-like claws, but in males the first and second pair of walking legs have strongly hooked "scissors", which are used for grasping the female during mating.

[12] These horseshoe crabs can be found to exist throughout southeast Asia in shallow waters with soft, sandy bottoms or extensive mud flats.

Scientists have studied the distribution of mangrove horseshoe crabs in Hong Kong specifically.

The researchers noted their abundance on the beaches of Hong Kong before the sharp decline in population over the past ten years.

They predict this unevenness is due to the estuarine hydrography in the western waters, influenced by the Pearl River.

[5] Studies have found that mangrove horseshoe crabs have a strong preference for insect larvae over the other organisms on which it also feeds.

[15] Once a mate is found, the female digs a hole and lays the eggs while the male externally fertilizes them.

[citation needed] Mangrove horseshoe crabs in Singapore breed from August to April.

[17] While the crabs have very little flesh, their roe is prized as a delicacy, in Thailand most commonly served as a salad called yam khai maeng da (ยำไข่แมงดา).