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The so-called ‘mimic octopuses’ of tropical Indonesia are reputed to mimic up to 13 species of other local marine organisms. We tested for mimicry by allowing individuals of two species of octopus to habituate to divers, then observing and filming two species continuously as they foraged daily in the same open, featureless volcanic sand habitat. Mimicry of a local, abundant flounder occurred commonly during 5 days of natural foraging: nearly 500 episodes were analysed. Both octopus species mimicked the shape, swimming actions, speed, duration, and sometimes the coloration of swimming flounders. During flounder mimicry, octopuses were actively moving and conspicuous, whereas immediately before and after flounder mimicry, they were camouflaged and motionless (sitting or very slowly crawling). Furthermore, when motionless, octopuses assumed body patterns and postures that resembled small sponges, tube-worm tubes, or colonial tunicates, which were among the few objects in the open sand habitat. The key finding was that octopuses used flounder mimicry only when their movement would give away camouflage in this open habitat. In all cases, octopuses used mimicry as a primary defense. Several interactions with fishes and stomatopods were filmed and typical secondary defense behaviours, not mimicry, were used by the octopuses. Foraging occurred twice per day and two tactile feeding tactics were used. Dens and food were not limiting; thus, we observed a highly unusual circumstance of a guild of small, long-armed octopus species that shared the same habitat, den sources, food, activity period, and some behaviours. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 23–38. [ABSTRACT FROM AUTHOR]

The flamboyant cuttlefish Metasepia pfefferi is renowned for its bold and colorful body patterns, yet the functions of these displays and other behaviors remain largely unknown. We conducted two field studies in Indonesia using SCUBA and video to record its behavior under natural conditions. Camouflage via background matching and masquerade is the common primary defense against predators, and is also used offensively to approach prey closely. This species rarely uses its "flamboyant" bright conspicuous displays in nature; they were observed only during courtship or as secondary defense when a large fish closely approaches it. Males are only 10–60% the size of females and they court her with a vivid and dynamic Flamboyant Display, which appears to be one of the most elaborate among cephalopods. Conversely, females remain camouflaged and show no conspicuous courtship behaviors. When two males courted or mate-guarded a single female, unilateral signaling of aggression was observed. Twenty matings were recorded among 5 pairs of cuttlefish; they were in the "head-to-head" position and lasted only 3 s. Females were choosy; they required males to court for long periods and rejected 50% of males that attempted to mate with them. Females lay ca. 25 eggs per batch, roughly 6–7 min apart, usually during morning hours and with no male present. They often deposit eggs in coconut shells that occupy this open sandy habitat. This small species is cryptic and spends the vast majority of each day in a variety of highly camouflaged body patterns. • The colorful Flamboyant Display is among the most elaborate of cephalopods. • The Display is seen only during courtship and mate guarding or very briefly as a startle response to predators. • Mating is brief (3 s) and females are very choosy. • This cuttlefish has superb camouflage and remains this way the vast majority of time. [ABSTRACT FROM AUTHOR]