An octopus,Ocythoe, with a swimbladder and triple jets

Abstract

A young female of the rarely seen pelagic octopodOcythoe 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 the upper chamber of the mantle cavity forwards, upwards, sideways or backwards. The dorsal sac or swimbladder lies on top of the visceral mass, has a duct into the mantle cavity, is supplied with a nerve and blood 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 µm thick. In a ripe (2.2 kg) specimen the walls are less gelatinous and the lumen is large and permanently expanded (volume 110 ml). The living ocythoe was negatively buoyant when delivered to the laboratory and regained and lost buoyancy 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 not known. Cephalopods have a variety of mechanisms for buoyancy control butOcythoeappears to be the only species with a swimbladder. The structure is absent in the dwarf male. Probably it is derived embryologically from the shell Anlagen.