FIRST PHOTOGRAPHIC RECORD OF MIMIC OCTOPUS, Thaumoctopus mimicus Norman and Hochberg, 2005 IN THE EAST ANDAMAN SEA, EASTERN INDIAN OCEAN

Thaumoctopus mimicus Norman and Hochberg, 2005 was observed and photographed in the coastal waters southwest of Phuket Island, Thailand in the Andaman Sea, in the eastern Indian Ocean. Morphological diagnostic characteristics of the colour patterns on the dorsal mantle were visible. Behavioural characteristics supported the morphological identification. This study confirms the distribution of this species across the Indo-Pacific region where records in the eastern Indian Ocean have formerly been scant. Phuket mar. biol. Cent. Res. Bull 46 and the dorsal web was the shortest one (Fig. 3). Arm suckers were biserial. A large and elongated supraocular papilla and a smaller antero-ocular papilla were presented on each eye (Fig. 4). Figure 1. Colour patterns on the dorsum, arrows indicate the white teardrop and U-patch and the white bands on the arms. Figure 2. Arrows indicating a colour pattern where the white teardrop on the dorsal mantle is fused with the U-patch. (Photo extracted from a video footage). First photographic record of mimic octopus 47 Figure 3. The mimic octopus displayed an oral “disc” of curled arms and webs during its defence mode in the water column, and was assumed to mimic a crinoid. Figure 4. The mimic octopus in its den, mimicking a jawfish. The papillae are observed above (left) and in front of the eyes (right) and are indicated by arrows. Behavioural Characteristics The behaviour supported the morphological identification. The octopus inhabited open plain substrates of estuarine mud, fine silt mud (observed in 3 dives) and muddy sand with coral gravel (1 dive). The solitary habit was a ritual behaviour, with an individual octopus occupying a den on the top of an elevation in front of the reef (Fig. 5). More than one octopus in a den was observed in the same area with a distance between dens of about 50‒100 m. It is not known whether the octopus made those dens or just occupied the vacated dens previously made by other animals. However, burrowing behaviour was observed as the animal inserted one arm into the substrate in an opening to a certain depth before burrowing. Insertion of an arm might act as a test for substrates. On hard substrates like coral gravel where the octopus could not easily burrow, the octopus would soon cease to burrow and would flee to other rock crevices or dens. While sitting in its den, the octopus mimicked a jawfish (Fig. 4). Foraging was diurnal and exhibited only at dawn and dusk, never at midday. Mimicry of a flatfish was demonstrated during swimming with strong disruptive colouration (Fig. 6). As a defence against intrusion by a diver the mimic octopus impersonated a lion fish in the water column (Fig. 7). Other mimicry displayed included that of a crinoid and a flatfish in the water column (Fig. 3) and on the substrate (Fig. 8). Phuket mar. biol. Cent. Res. Bull 48 Figure 5. The mimic octopus den on top of an elevation on a mud plain. Figure 6. Mimicry of a flatfish during swimming. First photographic record of mimic octopus 49 Figure 7. Mimicry of a lionfish as a defence behaviour in the water column. Figure 8. Mimicry as a crinoid or a brittle star on a gravel substrate.