Octopoda

Octopoda, an order of Cephalopoda (q.v.), including the Octopus or Devil Fish (the "pieuvre" of Victor Hugo) and the Argonauta or Paper Nautilus. The nearest ally is the order Decapoda (q.v.), from which it differs in the possession of eight instead of ten arms; in that these bear sessile and not stalked suckers, that the arms are connected at their lower ends by a thin membrane, and that the eyes have a sphincter-like lid. There are three families: - (1) the Cirrhoteuthidce, of which the type is the genus Cirrhoteuthis, which is a small violet-coloured species from the coast of Greenland; (2) Philonexidce or Argonautida1, including the Paper Nautilus; and (3) the Octopodidce, including the typical genus Octopus. The Octopods have, as a rule, no shell; in most of the order this is represented only by a few internal, small, calcareous rods. In Argonauta, however, two of the arms are expanded at their ends, and the flat plate-like membranes thus formed are folded back, and secrete a shell over the hinder part of the body. This is present, however, only in the females. In most of the Octopods one of the eight arms in the males is specialised to serve as a reproductive organ; it is usually separated from the male during copulation, and when discovered by the Italian naturalist, Chiaje was regarded as a parasitic worm and described under the name of Trichocephalus acetdbularis. Aristotle, however, who described the Argonaut, seemed to have understood its proper function. The Octopods are all marine; they either live in holes under rocks, as e.g. the ordinary Octopus, or swim on the surface often far from land. The only fossil representatives of the order are some shells of the Argonauta from the Cainozoic deposits. Octopus is not uncommon round the English coast and in the Channel Islands.