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SYNOPTIC DESCRIPTION OF THE PHYLUM PLATYHELMINTHES

SYNOPTIC DESCRIPTION OF THE PHYLUM PLATYHELMINTHES (GEGENBAUR 1859)

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> METAZOA> BILATERIA> PROTOSTOMATA> SPIRALIA> PLATYZOA> PLATYHELMINTHES
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Indtroduction

Hierarchical Classification

The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Nielsen (2001), Storer and Usinger (1965), Tudge (2000), and Walker and Anderson (2001).

I. SYNONYMS: flatworms.

II. NUMBER: >25,000 species known.

III. PHYLUM CHARACTERISTICS:

  • A. Structure
    • Symmetry: Bilateral
    • Body Cavity: Not present. Organ systems in parenchymatous mesoderm (text with tooltip) Parenchymatous mesoderm is connective tissue that fills the space between the musculature and the gut in acoelomates. .
    • Body Covering: Ciliated epithelium.
    • Support: Hydrostatic skeleton.
    • Digestive System: When present, it is a blind gut with an eversible pharynx (text with tooltip) The eversible pharynx is opening to the gut and feeding structure in turbellarians. or proboscis.
    • Circulatory System: None.
    • Locomotion: Ciliated epithelium and muscular contractions.
    • Excretory System: Protonephridia (text with tooltip) Protonephridia (protonephridium, sing.) are excretory organs that are ciliated tubules. The flame cell lies at the internal terminus ciliated tubule. ; tubes that begin with flame cells (text with tooltip) Ciliated cell that is part of the excretory system in Platyhelminthes, Rotifera, and Annelida. and emerge through nephridiopores.
    • Nervous System: Anterior ganglion (text with tooltip) A ganglion (ganglia, pl.) is a cluster of nerve cells. A brain is an enlarged ganglion. with 2 major lateral nerve cords (text with tooltip) A nerve cord is a major nerve that runs the length of most bilaterian animals. They are ventral in the protostomes and usually dorsal in the deuterostomes. ; turbellarians with ocelli.
    • Endocrine System: None.
  • B. Reproduction:
    • Reproductive System: Oviparous (text with tooltip) An oviparous (adj.) animal is one that releases eggs in its life cycle. They may be fertilized internally or externally. . Most are hermaphroditic (text with tooltip) An animal that bears both male and female gonads. though taxa like the blood flukes are dioecious with the mature male situated in the gynocophoral groove (text with tooltip) A gynecophoral groove is a ventral groove in a the female Schistosome (blood fluke) in which the smaller male resides. of the mature female. Sex organs complex with ovaries, a uterus, and testes in all taxa. Usually internal fertilization. Sperm biflagellated.
    • Development: Initial development by spiral cleavage (text with tooltip) Spiral cleavage is typical of the Protostomata and is characterized by the division planes of early cytokinesis products of the zygote being oblique to the plane of the polar axis. This produces unequal cells in the developing blastula. Usually spiral cleavage is determinant. . Parasitic (text with tooltip) A parasite is a symbiotic organism that benefits from the relationship at the expense of the host. species with complex life cycles. Often with alternation of hosts. Some with asexual (text with tooltip) As the name implies, asexual reproduction is the formation of offspring without the union of gametes. Usually, asexual reproduction involves the production of specialized cells or multicellular structures that can give rise to new individuals. stages.
    • See Life Cycles of the following for examples:
  • C. Ecology: Aquatic (freshwater and marine), terrestrial and parasitic.
LITERATURE CITED

Barnes, R. D. 1980. Invertebrate Zoology. Saunders College/Holt, Rinehart and Wilson, Philadelphia.

Barnes. R. S. K. 1984a. Kingdom Animalia. IN: R. S. K. Barnes, ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc., Sunderland, MA. pp. 129-257.

Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass.

Buchsbaum, R. 1938. Animals Without Backbones, An Introduction to the Invertebrates. The University of Chicago Press. Chicago.

Conway Morris, S. and J. S. Peel. 2008. The earliest annelids: Lower Cambrian polychaetes from the Sirius Passet Lagerstätte, Peary Land, North Greenland. Acta Palaeontol. Pol. 53(1): 137-148.

Darwin, C. R. 1881. The Formation of Vegetable Mould, Through the Action of Worms, With Observations on their Habits. John Murray. London.

Frelich, L., C. Hale, S. Scheu, A. Holdsworth, L. Heneghan, P. Bohlen, and P. Reich. 2006. Earthworm invasion into previously earthworm-free temperate and boreal forests. Biological Invasions. 8(6): 1235-1245.

Giribet, G., C. W. Dunn, G. D. Edgecombe, and G. W. Rouse. 2007. A modern look at the Animal Tree of Life. Zootaxa. 1668: 61-79.

Giribet, G., A., A. Okusu, A. R. Lindgren, S. W. Huff, M. Schrodl, and M. K. Nishiguchi. 2006. Evidence for a clade composed of molluscs with serially repeated structures: Monoplacophorans are related to chitons. Proc. Nat. Acad. Sci. USA. 103(20): 7723-7728.

Halanych, K. M. 2004. The new view of animal phylogeny. Annu. Rev. Ecol. Evol. Syst. 35: 229-256.

Halanych, K. M., T. G. Dahlgren, and D. McHugh. 2002. Unsegmented annelids? Possible origins of four lophotrochozoan worm taxa. Integ. and Comp. Biol. 42: 678-684.

Hickman, C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company. Saint Louis.

Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York.

McHugh, D. 1997. Molecular evidence that echiurans and pogonophorans are derived annelids. Proc. Nat. Acad. Sci. USA. 94: 8006-8009.

Meglitsch, P. A. and F. R. Schramm. 1991. Invertebrate Zoology. Oxford University Press, New York, Oxford.

Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford.

Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York.

Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. 6th edition. Saunders. Ft Worth, TX.

Ruppert, E. E., R. S. Fox, and R. D. Barnes. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole. New York. pp. 1-963.

Siddall, M. E., E. Borda, and G. W. Rouse. 2004. Toward a tree of life for Annelida. In: Cracraft, J. and M. J. Donoghue, eds. Assembling the Tree of Life. Oxford University Press. Oxford, New York. pp. 237-251.

Sigwart, J. D. and M. D. Sutton. 2007. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proc. Royal Society B. 274: 2413-2419.

Storer, T. I. and R. L. Usinger. 1965. General Zoology. 4th Edition. McGraw-Hill Book Company. New York.

Struck, T. H., N. Schult, T. Kusen, E. Hickman, C. Bleidorn, D. McHugh, and K. M. Halanych. 2007. Annelid phylogeny and the status of Sipuncula and Echiura. BMC Evolutionary Biology. 7:57 doi: 10.1186/1471-2148-7-57

Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York.

Walker, J. C. and D. T. Anderson. 2001. The Platyhelminthes, Nemertea, Entoprocta, and Gnathostomulida. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 59-85. [L]

Valentine, J. W. 2004. The Origin of Phyla. University of Chicago Press. Chicago. 614 pp.

Zrzavý, J., P. Ríha, L. Piálek, and J. Janouskovec. 2009. Phylogeny of Annelida (Lophotrochozoa): total-evidence analysis of morphology and six genes. BMC Evolutionary Biology. 9:189 doi: 10.1186/1471-2148-9-189
By Jack R. Holt. Last revised: 01/29/2012
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