AN OCTOPUS, OCYTHOE, WITH A SWIMBLADDER AND TRIPLE JETS

A young female of the rarely seen pelagic octopod Ocythoe tuberculata (Rafinesque, 1814) (Argonautoidea) survived for two days in captivity. It possessed a swimbladder and controlled its buoyancy. When swimming , the dorso-lateral corners of the mantle aperture were converted into dirigible structures ('accessory funnels'), which jetted water from t he upper chamber of the mantle cavity forwards, upwards, sideways or b ackwards. The dorsal sac or swimbladder lies on top of the visceral ma ss, has a duct into the mantle cavity, is supplied with a nerve and bl ood vessels and in immature specimens has thick gelatinous walls which contract peristaltically and contain spherical 'amoeboid' cells. The lumen is lined by a cuboidal epithelium 7 mu m thick. In a ripe (2.2 k g) specimen the walls are less gelatinous and the lumen is large and p ermanently expanded (volume 110 ml). The living ocythoe was negatively buoyant when delivered to the laboratory and regained and lost buoyan cy twice during captivity. On one occasion it was observed to release gas as it plunged to the bottom. The origin and nature of the gas is n ot known. Cephalopods have a variety of mechanisms for buoyancy contro l but Ocythoe appears to be the only species with a swimbladder. The s tructure is absent in the dwarf male. Probably it is derived embryolog ically from the shell Anlagen.