It has two parts; front part (prosoma) is bigger and covered in spines, while the back section (opisthosoma) is smaller and smoother. Around the mouth, there are six pairs of leg-like appendages on the head (prosoma) – a tiny pair in the front and five larger ones on each side.. A long, spiky tail (telson) is a distinctive feature of this creature. The tail has a triangular shape due to a ridge on its top (dorsal crest) and a curved underside (ventral concavity). External skeleton (chitinous exoskeleton) is sage green in color. Shell is round and brown. The tail is round in cross-section near the body, and it has shorter spines on the sides. It does not have a groove on the underside or spines on the upper side. Horseshoe crab is actually a species under Phylum Arthropoda but it does not belong to Subphylum Crustacea.