Mangrove horseshoe crab

Description

The mangrove horseshoe crab (Carcinoscorpius rotundicauda), also known as the round-tailed horseshoe crab, is a chelicerate arthropod found in tropical marine and brackish waters in India, Bangladesh, Indonesia, Malaysia, Brunei, Singapore, Thailand, Cambodia, Vietnam, China and Hong Kong. It may also occur in Sri Lanka, Myanmar and the Philippines, but confirmed records are lacking. Despite their name, horseshoe crabs are more closely related to spiders and scorpions (all are in the subphylum Chelicerata) than to crabs. Recent phylogenetic analysis suggests that horseshoe crabs may themselves be arachnids. The mangrove horseshoe crab is the only species in the genus Carcinoscorpius. There are four extant (living) species of horseshoe crab. 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. This species occurs only in Asia around the Indo-West Pacific region where the climate is tropical or subtropical. These horseshoe crabs can be found to exist throughout southeast Asia in shallow waters with soft, sandy bottoms or extensive mud flats. The mangrove horseshoe crab is benthopelagic, spending most of its life close to or at the bottom of a body of their brackish, swampy water habitat, such as mangroves. This is the habitat for which it gains its common name: mangrove horseshoe crab. 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. In the study, they found an uneven distribution of the horseshoe crabs throughout Hong Kong, with a greater abundance found in the western waters. They predict this unevenness is due to the estuarine hydrography in the western waters, influenced by the Pearl River. They also found that T. tridentatus can coexist in the same habitat as the mangrove horseshoe crab.