Amplexus occurs in all four species of horseshoe crab. Horsefoot refers to a horseshoe crab. The harvesting of horseshoe crab blood in the pharmaceutical industry is in decline. There are four extant (living) species of horseshoe crab. Studies of microsatellite DNA have revealed several distinct geographic groups in the Atlantic horseshoe crab. The tri-spine horseshoe crab is the largest of the living horseshoe crab species. Development along shorelines is dangerous to horseshoe crab spawning, limiting available space and degrading habitat. Since its inception, the ERDG has made significant contributions to horseshoe crab conservation. Tetrodotoxin may be present in one horseshoe crab species, "Carcinoscorpius rotundicauda". A protein from horseshoe crab blood is also under investigation as a novel antibiotic. The horseshoe crab is an arthropod of the family Limulidae. The possibly endangered horseshoe crab is also found in this region. Although most arthropods have mandibles, the horseshoe crab is jawless. If they are kept moist, the horseshoe crab can live on land for many hours.