Four pairs of small leaf-like structures, called swimmerets, are found under the tail. Female spiny lobsters carry their eggs in the swimmerets. To distinguish between the sexes, examine the underside of the cephalothorax. In the male, sperm duct openings are found at the base of the fifth pair of walking legs, those nearest the tail section. The sperm ducts become greatly enlarged during the breeding season.
Male swimmerets are single and paddle-like.
Female swimmerets are bilobed, resembling small pincers and, as noted, carry the eggs. The fifth pair of legs of the female is adapted for tending the eggs. Spiny lobsters vary in color. They may range from very light, almost white, to very dark, almost black or red-orange. In general, spiny lobsters from inshore, shallower waters are lighter in color than those from deeper reefs.