Marine invertebrates

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The 49th plate from Ernst Haeckel's Kunstformen der Natur, 1904, showing various sea anemones classified as Actiniae, in the Cnidaria phylum

Marine invertebrates are multicellular animals that inhabit a marine environment and are invertebrates, lacking a vertebral column. In order to protect themselves, they may have evolved a shell or a hard exoskeleton, but this is not always the case.

As on land and in the air, invertebrates make up a great majority of all macroscopic life in the sea. Invertebrate sea life includes the following groups, some of which are phyla:

Ernst Haeckel's 96th plate, showing various invertebrates classified as Chaetopoda in the Annelida phylum
  • Myzostomida, a taxonomic group of small marine worms which are parasitic on crinoids or "sea lilies";
  • Nemertinea, also known as "ribbon worms" or "proboscis worms";
  • Orthonectida, a small phylum of poorly known parasites of marine invertebrates that are among the simplest of multi-cellular organisms;
  • Phoronida, a phylum of marine animals that filter-feed with a lophophore (a "crown" of tentacles), and build upright tubes of chitin to support and protect their soft bodies;
  • Placozoa, small, flattened, multicellular animals around 1 millimetre across and the simplest in structure. They have no regular outline, although the lower surface is somewhat concave, and the upper surface is always flattened;
  • Porifera (sponges), multicellular organisms that have bodies full of pores and channels allowing water to circulate through them;
  • Priapulida, or penis worms, are a phylum of marine worms that live marine mud. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis;
  • Pycnogonida, also called sea spiders, are unrelated to spiders, or even to arachnids which they resemble;
  • Sipunculida, also called peanut worms, is a group containing 144–320 species (estimates vary) of bilaterally symmetrical, unsegmented marine worms;
  • Tunicata, also known as sea squirts or sea pork, are filter feeders attached to rocks or similarly suitable surfaces on the ocean floor;
  • Some flatworms of the classes Turbellaria and Monogenea;
  • Xenoturbella, a genus of bilaterian animals that contains only two marine worm-like species;
  • Xiphosura, includes a large number of extinct lineages and only four recent species in the family Limulidae, which include the horseshoe crabs.

Minerals from sea water[edit]

There are a number of marine invertebrates that use minerals that are present in the sea in such minute quantities that they were undetectable until the advent of spectroscopy. Vanadium is concentrated by some tunicates for use in their blood cells to a level ten million times that of the surrounding seawater.[1] Other tunicates similarly concentrate niobium and tantalum.[1] Lobsters use copper in their respiratory pigment hemocyanin, despite the proportion of this metal in seawater being minute.[2] Although these elements are present in vast quantities in the ocean, their extraction by man is not economic.[3]

See also[edit]

References[edit]

  1. ^ a b Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 947. ISBN 81-315-0104-3. 
  2. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 638. ISBN 81-315-0104-3. 
  3. ^ Carson, Rachel (1997). The Sea Around Us. Oxford Paperbacks. pp. 190–191. ISBN 0195069978.