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ANNELIDA

ANNELIDA. I. Phylum Annelida – Segmented Worms. A. Characteristics. 1. Metameric body plan (internal segmentation as well as external) . 2. vermiform body (vermiform = wormlike) 3. bilateral symmetry 4. protostomates. spiral cleavage determinant development

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ANNELIDA

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  1. ANNELIDA

  2. I. Phylum Annelida – Segmented Worms A. Characteristics 1. Metameric body plan (internal segmentation as well as external) 2. vermiform body (vermiform = wormlike) 3. bilateral symmetry 4. protostomates • spiral cleavage • determinant development • schizocoelus coelom development (eucoelom) 5. Trochophore larva (links the mollusks with the annelids) 6. paired epidermal setae (setae are bristles or hairs)

  3. Setae 4. Hypodermis • Coelom 5. Circular Muscle • Cuticle 6. Longitudinal Muscle

  4. 7. Ventral nerve cord 8. closed circulatory system 9. excretory organs are metanephridia (most common) with a few retaining the protonephridia

  5. B. Benefits or adaptive advantages of a metameric body plan • greater flexible support • more efficient locomotion • specialization of body regions (segments)… this specialization is called tagmatization (tagma = arrangements) a. because of this tagmatized bodies, annelids and arthropods are thought to be fairly closely related C. Class Polychaeta – “many bristled worms” • most primitive of the annelids • largest class of annelids with 5300 species • many are members of the infauna buried in muds or sands

  6. 4. many other species form tubes on the surface of the substrate, members of the epifauna 5. the most distinctive features are the presence of lateral extensions called parapodia a. the parapodia terminate in setae or bristles at their tips • aid in locomotion • 2) aid in burrowing 3) some are venomous and aid in defense

  7. 6. prostomium – this is the segment (lobe) that projects out before the mouth and has sensory organs located on it (eyes, antennae, palps, and nuchal organs) 7. peristomium – literally “around the mouth” – this is the first body segment at it surrounds the mouth

  8. 8. cuticle – tough, protective outer covering ( a few polychaetes have bioluminescent cuticles) 9. Feeding: • predators – these have a proboscis with paired jaws and some are venomous • deposit feeders – feed on organic debris that falls on the substrate near their burrow c. suspension feeders – capture particles suspended in the water column on their extended gills

  9. 10. gas exchange occurs through their skin directly into their blood stream 11. they excrete ammonia as a waste 12. they demonstrate fair powers of regeneration 13. fertilization is usually external…eggs and sperm are released into the water 14. most species are marine 15. one species of worm, the palolo worm, is eaten by Samoan tribes from the South Pacific

  10. D. Class Oligochaeta – “few bristled” worms • most species are either terrestrial or freshwater (total of 3,000 species) • have few bristles on each segment (earthworms have but two pair on each segment) • have five pairs of “hearts” or pumping organs called aortic arches • these worms may have a swollen area behind their heads called a clitellum that plays a roll in reproduction. …these worms are monoecious and the clitellum secretes a mucus that surrounds both worms during mating so that each worm can pass sperm to the other within this protected mucus

  11. 5. they demonstrate dermal respiration (gases go right through the skin) • a worm’s skin cannot get too dry, otherwise gasses cannot dissolve through the skin • most worms also cannot be submerged in water or else they drown 6. demonstrate negative phototaxis (do not like light) 7. digestive system consists of the following: mouth ------> pharynx (suctioning organ) -------> esophagus -------> crop (storage organ) ----------> gizzard (grinding organ) ------> intestine (absorption) -----> anus

  12. 8. as in all annelids, oligochaetes have inner walls called septa (septum, singular) separating each of their segments D. Class Hirudinea • This class includes the leeches • leeches are considered to be external parasites, but they are better thought of as short term, non-lethal predators • leeches have no setae nor bristles • Some leeches eat small arthropods and are not blood-suckers • most leeches are freshwater, but a few are marineproduce • both produce an anesthetic (so that the bite cannot be felt) and an enzyme, hirude, that acts as an anti-coagulant so that blood flows freely and does not form clots

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