Earth and Life Through Time;

Historical Geology, and Geological History.


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  1. Historical account
  • Definition of the phylum- Endoparasitic, pseudocoelomate, and wormlike Bilateria, lacking a digestive tract, with the anterior end formed into an invaginated proboscis armed with hooks.
  • External features:
    • Body is elongated, becoming tapered at both ends, with size ranging from 1.5mm-.5m in length.
    • Body wall is covered with a thin epicuticle of muccopolysacchorides and a noncelbular cuticle (1 micron or less).
    • Body is divided into two major regions- the presoma and the trunk.
      • Presoma is composed of the proboscis- a retractile organ armed with hooks and spines, and the neck- an unarmed region  posterior to the proboscis.
      • Trunk is the major bulk of the animal, surface may be smooth, wrinkled, or irregularly ringed; some genera arm the trunk with spines.
    • Proboscis serves as an attachment organ within the hosts intestine or for locomotion.
      • Contains alternating rows of hooks and spines in a definite pattern.
      • Hooks are larger structures with roots sunken deep in proboscis walls; spines are smaller structures lacking roots.
      • Proboscis is invaginable and can be withdrawn into a muscular sac – the proboscis receptacle.
      • Proboscis musculature-
        • retractors: attach to base of proboscis sheath and run posteriorly dividing into ventral and dorsal retractors; function to withdraw proboscis into receptacle.
        • protractor: originate in a circle at the base of neck and attach to posterior end of sheath; function to extend proboscis out of receptacle.
    • Sense Organs are generally deficient and are of a tactile nature.
      • Proboscis contains a terminal, small pit with a nerve ending.
      • Male bursa and penis have genital ganglion which terminate into bulbous or spherical sense organs.
    • Usually lack coloration but may appear red, orange, yellow or brown due to absorption of food.

Written by infiniteintimation

September 9, 2011 at 4:00 am

Posted in Life

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