Body except for caudal peduncle covered with dermal plates. Carapace elongated pentagonal in transverse section, closed behind dorsal and anal fins. Dorsal ridge sharp, extending from nape to origin of dorsal fin. A short spine projecting forward from eye. Interorbital space concave. A spine projecting posteriorly from posteroventral corner of carapace. An isolated small dermal plate on dorsal and ventral sides of caudal peduncle in many individuals. Caudal fin rounded. Origin of anal fin posterior to last ray of dorsal fin. Body yellowish brown with irregular blue lines and blotches; cheek with several longitudinal blue lines.
Distribution:
Warm and tropical regions of Atlantic; in the western Atlantic from Massachusetts to Brazil.
Remarks:
This species is similar to A. polygonius but differs from it by having 11 pectoral fin rays and several irregular blue lines on the cheek. (Matsuura)