Chp 13 Annelida

1
Chp 13 Annelida

• The Metameric Body Form

2
Dissection of Earthworm

• The earthworm belongs to a group of animals
  called annelids (segmented worms).
• The body of an annelid is usually divided
  internally and externally into well-defined
  segments which may be separated from each other
  by membranous partitions.
• Except for the tail and head regions, all
  segments are essentially alike.

3
Others

• Others members of this group include the clam
  worms and tube worms and tube worms, which live
  in the ocean, and the leeches.

4
Feeding

• The earthworm hunts food at night and thus has
  been called a night crawler.
• It usually extends its body from the surface
  opening of a small tunnel which it makes by
  eating its way through the soil.
• The rear end of the worms body remains near the
  opening while the head end forages for decaying
  leaves and animal debris.

5
Where To Find Earthworms

• It has been estimated that an acre of good soil
  contains over 50,000 earthworms.
• By their continuous foraging and tunneling these
  worms turn over 18 to 20 to tons of soil of soil
  per acre and bring over one inch of rich soil to
  the surface every four to five years.
• Thus, indirectly the earthworm enriches farmland
  and provides for more food in a rapidly
  expanding population.

6
Parts of the Earthworm

• At the anterior (front) end is a small fleshy
  projection over the mouth. This is the
  prostomium. It is not considered to be a segment
  of the worm.
• The anus, the opening at the end of the digestive
  tract through which solid wastes are exposed,
  will be found at the posterior (hind) end.
• About one-third of the way back from the mouth
  region is a thick cylindrical collar---the
  clitellum. This structure, involved in
  reproduction, will be considered later.
• If you lightly stroke the ventral surface in an
  anterior direction, the bristles you feel are the
  setae and are the setae and are used by the worm
  in movement.
• Each segment (except the first three and the last
  1) have pores.
• The small openings connect with the metanephridia
  which are the primitive kidneys of the earthworm.
• Each segment of the worm is separated from the
  next one by a thin wall called a septum.

7
Digestive System

• Mouth the opening is located just below the
  overlapping prostomium.
• Esophagus passes food with muscular contractions
• Crop stores food
• Gizzard grinds up food
• Intestine digestion and absorption
• Anus expels waste

8
Parts of the Earthworm Cont.

• Shantell T. Roberson do not want to disect worms
  Mr. Davis.