Carcinoscorpio spp., Limulus polyphemus, Tachypleus spp. (Horseshoe crabs) About 24" long, Eastern Atlantic, Eastern Pacific. 100 gal aquarium or larger recommended, their preferred prey are animals living in a deep sand bed. Will scavenge most meaty aquaium foods. Not suited to most home aquariums. Tend to starve in most systems. They can strip a sand bed of noticeable life, after which they starve. They can easily becomed wedged in live rock formations. Normally not recommended. try some oyster, squid, or clam. I suspect the animal is feeding or worse. hope something here helps.