Recently while examining a living specimen of the sea pen, Pteroeides esperi Herklots**, brought up in a shore seine at Vedalai near Mandapam on the Gulf of Mannar, a porcellanid crab, the colour pattern of which resembled that of the host to a remarkable degree, was found sheltering between the pinnules (Plate I, fig. 1). The camouflage was so perfect that it was difficult at a casual glance to spot the crab, the general colour of which (Plate 1, fig. 2 inset) was whitish as that ofthe sea pen while the carapace and chelipids had dark more or less symmetrically arranged spots, simulating to some extent the dark spots on the distal part and margin ofthe pinnules (Plate I, fig. 1 inset). Attempts to dislodge the crab automatically disturbed the sea pen which reacted immediately by shrinking. This reduced further the interspace between the pinnules, thereby affording greater protection to the crab. The crab in turn clasped firmly on to the body of the sea pen and only with considerable difficulty could it be separated without inflicting any da. ^e. When thus separated from the host and placed in another part of the aquarium tank it moved about till it could get on the sea pen again

Porcellanella sp. Pteroeides esperi, animal association, Gulf of Mannar