1. Tachypleus scorpionus (scientific name: Carcinoscorpius rotundicauda): the smallest of the Limulus species, with a body length of 40 cm (plus tail length).
 2. The body of the horseshoe crab is divided into three parts: the largest part is the head and chest, then the segmented abdomen, and then a long pointed tail thorn.
 3. It has a pair of compound eyes on the side of its head and chest, and each eye is composed of several small eyes.
 4. In addition, there is a pair of monocular eyes that can feel ultraviolet rays.
 5. They also have a pair of pincers, called pincers, which are used to prey on worms and thin shelled mollusks.
 6. Generally, the habitat is in muddy rivers, estuarine marshes and mangroves, and in estuaries with low salinity.
 7. Unlike other species of this genus, it does not return to the sea when the tide is low.
 8. Adult horseshoe crabs are mostly found in deep water, while juvenile horseshoe crabs are mostly found in shallow water of intertidal zone.
 9. It is distributed in India, Indonesia, Malaysia, the Philippines, Singapore and Thailand.