suckers of less than 0.2 mm in diameter and 18 to 25 teeth. The strong, curved, and short beaks (rostra) are mostly black to dark brown. The radula has seven rows of teeth. The spermatophores of males are about long and 0.15 mm wide. The ink sac is pear-shaped, with a silvery blue-green outer layer. The vane of the gladius (the rigid internal remnants of the mollusc shell) is oval-shaped and pointed at both ends (lanceolate). It has a broad midrib (rachis). The eight arms are thick, tapering to a narrow point. They are unequal in length, with arm pair I the shortest, followed by arm pair II and arm pair IV, and arm pair III the longest. All of them possess two rows of suckers. Each sucker has a diameter less than , decreasing distally, and a ring of 17 to 28 sharp acute teeth. The left arm of pair IV in males is modified into a sexual organ known as the hectocotylus. They bear long fleshy protrusions (papillae) with toothless suckers at the distal portion. The tentacles are thick and long, extending the length of the mantle when retracted. They are slightly compressed laterally. A prominent ridge (a keel) is present on the outer surface of each of the tentacle clubs (the wide tip of the tentacles). There are four rows of suckers on the manus (proximal part of the club) and the dactylus (distal part of the club). The larger suckers in the centre of the manus have 17 to 18 widely spaced teeth. Coloration Large chromatophores densely cover the upper surfaces of the head, mantle and arms. They are distributed more sparsely on the ventral side. The fins do not possess chromatophores on the underside. Living specimens range in colour from translucent creamy white through pale yellow to brownish pink and brownish violet. Like some other cephalopods, bigfin reef squids are capable of metachrosis – rapidly changing body colouration and patterns through voluntary control of chromatophores. They also possess iridophores (particularly in the head), a form of structural colouration that produces iridescent metallic greens and red when illuminated. They are also possibly one of two squid species with leucophores. Leucophores are a reflector-type structural colouration that reflects ambient light, such that they are white in white light, green in green light, and so on. Bigfin reef squids are remarkable for having the ability to produce complex