File:The fauna of the deep sea (1894) (14576801340).jpg

Identifier: faunaofdeepsea01hick (find matches)
Title: The fauna of the deep sea
Year: 1894 (1890s)
Authors: Hickson, Sydney John, 1859-1940
Subjects: Marine animals
Publisher: New York D. Appleton and Company
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Smithsonian Libraries

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0 fathoms.Out of the twenty-seven known genera, only fiveextend into the abyss, and not one of these can becalled a true deep-sea genus. There are three genera, Nymj^hon, Collosendeis,and PhoxicJiilidium, that show a very wide distribu-tion over the floor of the ocean, and are capable ofexisting at the greatest depths, and of these thespecies of the genus Nymphon have a truly remark-able range extending from the shore to a depth of2,225 fathoms. As a rule, says Hoek, the deep-sea species areslender, the legs very long and brittle, and the sur-face of the body smooth. They have further, eitherno eyes at all or rudimentary eyes without pigment,and in many cases—as, for example, Collosendeis—they are distinguished for reaching to a gigantic sizecompared with their shallow-water relatives. The Tunicata is the group of animals thatincludes all those curious vegetable-like organismsfound upon our coasts that are familiarly known assea-squirts, or Ascidians, besides the salps, pyrosomas,
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142 THE FAUNA OF THE DEEP SEA and the microscopic appendicularias of the pelagicplankton. Notwithstanding the apparent simplicity of theiradult structure, naturalists are now agreed that theymust be removed from the Mollusca, with which theyhave hitherto been most frequently associated, andplaced in the group of the Vertebrata. It is thestudy of embryology that has led to this unexpectedconclusion, for we find, when we study the larval forms,that they possess both a notochord and gill-slits, twofeatures that are characteristic of the group of theVertebrata. The species of the group Perennichordata, whichincludes all those Tunicates that possess a noto-chord persistent through life, are chiefly pelagic inhabit, the little creatures, rarely more than two orthree millimetres in length, swimming or driftingabout with the sagittas, copepods, ctenophores, andmedusae that compose the pelagic plankton. Fol hasrecently described a gigantic form belonging to thisgroup, reaching a size of thirty

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