CLIO'N1D2E, the Clio Tribe, a family of Naked Marine Mollusea, placed by Cuvier as the first of his class Pteropoda. Lamarck also arranges them under the Pteropods, which he makes an order, but gives them a situation immediately after the Hyalceidce. De Blainville unites the Pteropoda and Gastropoda of Cuvier in one class Para cephalophora, under which the Pteropoda form an order with the name of Aporobranchiata, which is divided into two families ; the first, Theessomata, being provided with a shell, and the second, Gymnosomata, comprising those Pteropods which have none. Rang follows this last arrangement, still retaining Cuvier's term Pteropoda, but not rejecting De Blainville's, and making the species of Clio of Ferussac synonymous with the Gymnosomata of De Blainville, and the second family of the class Pteropoda.
Gymnosomata.—Body of an elongated form, sub-conical, completely naked : two bundles of tentacular suckers at the mouth ; no tooth in the upper lip ; a small lingual plate bristled with spines.
Rang thus defines the family :—Animal with the head distinct ; no intermediate lobe, but one or more fleshy appendages in place of it ; a muscular envelope or mantle.
Clio (Clione, Pallas).—Body free, naked, more or less elongated, a little depressed, attenuated abaft (aminci en arriere), without any other fins than the lateral appendages. Head very distinct, provided with six long retractile tentacula, divided into two groups of three each, and capable of being entirely concealed in a species of prepuce bearing a small tentaculum on its external side. Mouth entirely terminal and vertical. Eyes sessile, nearly supernal. A sort of sticker or rudiment of a foot under the neck, between the roots of the fins. Vent and termination of the generative apparatus in a single tubercle, situated at the right side of the neck, at the junction of the fin with trunk. Organs of respiration (l).
a. Species whose tentacula are well known.
Of these, C. borealis and C. australis will serve as examples. The
former, which appears to be the same with C. limacina of Phipps, C.retusa of Fabricius, and Clione papilionacea of Pallas, is well-known to the whale-fishera and others under the name of ' whale's food.' The species swarms in the northern seas, and indeed so plentiful are they that they form a principal part of the food of the whale bone whales. Captain (now Sir W. E.) Parry found it in great abundance in all parts of Baffin's Bay and Davis's Strait, in the neighbourhood of ice. (` Supplement to Captain Parry's first Voyage.') Captain James Ross observes that it is very numerous in most parts of the Arctic Ocean, but less abundant in Regent's Inlet and the Gulf of Boothia. When the weather is calm, they come in myriads to the sur face for the purpose of respiration; but scarcely have they reached it when they again precipitate themselves towards the bottom. Cuvier, who gives this account of their habits, adds, that the sea is so glutted with them in certain seasons, that the whales, so to speak, cannot open their mouths without ingulphing thousands of these small mollusks.
Integument, a delicate demi-transparent soft skin, which covers a second tunic. This last is thicker, and presents longitudinal and very sensible muscular fibres, which come from two principal bundles attached to the sides of the neck. The effect of these fibres must be to shorten the general envelope of the body, and to approximate its form to a spherical shape. Cuvier, who gives the above description, adds, that he knows not with ;what the interval between this fleshy tunic and the mass of the viscera is filled in the living state; but observes that it is certain that these do not occupy the half of the area which the tunic Meioses; and conjectures that there may be a liquor diffused there, or perhaps only a quantity of air which the animal can compress at pleasure when it would sink in the water, and dilate when it would rise.