Carcinoscorpius

The mangrove horseshoe crab (Carcinoscorpius rotundicauda), also known as the round-tailed horseshoe crab, is a species of horseshoe crab, a chelicerate arthropod found in tropical marine and brackish waters of India, Bangladesh, and Southeast Asia. It may also occur in Sri Lanka, Myanmar and the Philippines, but confirmed records are lacking. It is the only species in the genus Carcinoscorpius.

The biology, ecology and breeding patterns of C. rotundicauda and the two other Asian horseshoe crab species, Tachypleus gigas and Tachypleus tridentatus, have not been as well documented as those of the North American species Limulus polyphemus. All four extant species of horseshoe crabs are anatomically very similar, but C. rotundicauda is considerably smaller than the others and the only species where the cross section of the tail (telson) is rounded instead of essentially triangular.