Ribbon worms are unsegmented

The carnivorous ribbon worms (phylum Nemertea) are dorsoventrally flattened. They have nervous and excretory systems similar to those of flatworms, but unlike flatworms, they have a complete digestive tract with a mouth at one end and an anus at the other. Food moves in one direction through the digestive tract and is acted on by a series of digestive enzymes. Small ribbon worms move by beating their cilia. Larger ones employ waves of muscle contraction to move over the surface of sediments or to burrow. Movement by both of these methods is slow.

Within the body of nearly all of the 900 species of ribbon worms is a fluid-filled cavity called the rhynchocoel, within which lies a hollow, muscular proboscis. The proboscis, which is the feeding organ, may extend much of the length of the worm. Contraction of the muscles surrounding the rhyn-chocoel causes the proboscis to be everted explosively through an anterior opening (Figure 32.21) without moving the rest of the animal. The proboscis of most ribbon worms

Floating in a cavity called the rhynchocoel, the proboscis can be everted rapidly.

Proboscis' pore

Proboscis retractor muscle

Anus

Floating in a cavity called the rhynchocoel, the proboscis can be everted rapidly.

Proboscis retractor muscle

Proboscis' pore

Rhynchocoel

Anus

Everted proboscis

The tip of the proboscis bears sharp, nail-shaped stylets.

Everted proboscis

(b) Pelagonemertes sp.

The tip of the proboscis bears sharp, nail-shaped stylets.

(b) Pelagonemertes sp.

Ribbon Worm Proboscis
32.21 Ribbon Worms (a) The proboscis is the ribbon worm's feeding organ. (b) This deep-water nemertean displays an everted proboscis.

Ganglion in ventral nerve cord

Brain

Ring vessels of circulating system

Circular

Longitudinal muscle

^Blood vessel -Coelom

Intestine

Ganglion in ventral nerve cord

Ring vessels of circulating system

Circular

Longitudinal muscle

Brain

Earthworm Muscular Circular

Intestine

Setae (bristles)

Blood vessels

Sperm receptacles Testes and sperm sacs Ovary Oviduct Sperm duct

Wall

Segments

Coelom

Excretory organs

Setae (bristles)

32.22 Annelids Have Many Body Segments

The segmented structure of the annelids is apparent both externally and internally. Most organs of this earthworm are repeated serially.

Sperm receptacles Testes and sperm sacs Ovary Oviduct Sperm duct

Wall

Segments

Coelom

Excretory organs

Setae (bristles)

is armed with a sharp stylet that pierces the prey. Paralysis-causing toxins produced by the proboscis are discharged into the wound. Reproduction and development in ribbon worms is highly varied.

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Responses

  • SINIKKA
    What is Proboscis in rhynchocoel?
    8 years ago
  • alastair
    What is the sperm ducts of a worm?
    8 years ago
  • Philipp
    Where is the circular muscle on a worm?
    8 years ago
  • Julia
    What segment of the earthworm is the dorsal blood vessel?
    8 years ago
  • Cosma
    Where is the longitudinal nerve in a worm?
    8 years ago
  • SAMUEL TESFALEM
    Are a worms ganglion or brain bigger?
    8 years ago
  • riia
    Where are the sperm sacs located in an earthworm?
    8 years ago
  • martin
    Where are the oviducts on a worm?
    8 years ago

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