PHYLUM ANNELIDA (SEGMENTED WORMS)
• 12,000 species are known.
• They live in many different habitats (ocean, fresh water, damp soils).
TYPES
Oligochaeta - Earthworms.
Hirudinea - Leeches.
Polychaeta - Marine worms, clam worms, etc.
SYMMETRY
Bilateral
REPRODUCTION
Sexual or Asexual. Asexual reproduction occurs through fragmentation, budding, and fission. Most species have separate sexes. Some species are hermaphroditic. With regard to more sexual reproduction, sperm are passed between two worms near segments called the clitella, which produces the cocoon from which earthworms hatch. Sperm and eggs pass into the cocoon as it slips forward off the body of the cocoon. After fertilization, the young are protected in the cocoon until they are born.
BODY PLAN
Annelids are segmented coelomate worms, most of which live in the sea. The annelid body is composed of numerous similar segments. No legs. No hard skeleton. Multiple segments including a body cavity (coelom), movable bristles, and a segmented body. The fluid within the coelom of each segment makes a rigid support system. This rigidity in annelid segments creates a hydrostatic skeleton against which muscles can push. Segmentation also allows these segments to move independently of one another. It also allows worms to survive damage to a segment because other segments with the same function exist. Each segments contain structures for digestion, excretion, and locomotion. Some segments can be specialized (some may be adapted for sensing while others may be adapted fro reproduction).
DIGESTIVE SYSTEM
They have an unsegmented gut (digestive tract) that runs through all of their segments from the mouth to the anus. It is a tube within a tube. Food and soil taken in by the mouth pass through the pharynx into the crop, where they are stored until the pass to the gizzard, a muscular sac containing hard particles that help grind soil and food before they pass into the intestine. Nutrients are absorbed in the intestine. Then, undigested material passes out of the worm's body through the anus.
CIRCULATORY SYSTEM
Closed circulatory system. Has five hearts.
NERVOUS SYSTEM
Earthworms have a primitive brain, or ganglionic mass, located in the head. This mass is connected by a ring of nerves to the central nerve cord that spans the length of their body. Perhaps this enables them to detect light and vibration even though they do not have eyes. This system also controls its reproduction habits (such as creating the cocoon . They also have many cerebral organs that connect t the central nerve. Leeches have a somewhat different nervous system; their nervous system contains many optic nerve cords running along the body where it's transmitting information from their many (at least 10) eyes. It's nervous system also is in charge of maintaining it's hematophagous system, the same system used to suck blood from a host.
MY THOUGHTS
I learned that Charles Darwin studied worms. It is interesting that hey breathe through their skin, and can detect light and vibration, even though they do not have eyes. Finally, it is also interesting that some parasitic annelids have pouches along the digestive tract that hold enough food to last for months.
• They live in many different habitats (ocean, fresh water, damp soils).
TYPES
Oligochaeta - Earthworms.
Hirudinea - Leeches.
Polychaeta - Marine worms, clam worms, etc.
SYMMETRY
Bilateral
REPRODUCTION
Sexual or Asexual. Asexual reproduction occurs through fragmentation, budding, and fission. Most species have separate sexes. Some species are hermaphroditic. With regard to more sexual reproduction, sperm are passed between two worms near segments called the clitella, which produces the cocoon from which earthworms hatch. Sperm and eggs pass into the cocoon as it slips forward off the body of the cocoon. After fertilization, the young are protected in the cocoon until they are born.
BODY PLAN
Annelids are segmented coelomate worms, most of which live in the sea. The annelid body is composed of numerous similar segments. No legs. No hard skeleton. Multiple segments including a body cavity (coelom), movable bristles, and a segmented body. The fluid within the coelom of each segment makes a rigid support system. This rigidity in annelid segments creates a hydrostatic skeleton against which muscles can push. Segmentation also allows these segments to move independently of one another. It also allows worms to survive damage to a segment because other segments with the same function exist. Each segments contain structures for digestion, excretion, and locomotion. Some segments can be specialized (some may be adapted for sensing while others may be adapted fro reproduction).
DIGESTIVE SYSTEM
They have an unsegmented gut (digestive tract) that runs through all of their segments from the mouth to the anus. It is a tube within a tube. Food and soil taken in by the mouth pass through the pharynx into the crop, where they are stored until the pass to the gizzard, a muscular sac containing hard particles that help grind soil and food before they pass into the intestine. Nutrients are absorbed in the intestine. Then, undigested material passes out of the worm's body through the anus.
CIRCULATORY SYSTEM
Closed circulatory system. Has five hearts.
NERVOUS SYSTEM
Earthworms have a primitive brain, or ganglionic mass, located in the head. This mass is connected by a ring of nerves to the central nerve cord that spans the length of their body. Perhaps this enables them to detect light and vibration even though they do not have eyes. This system also controls its reproduction habits (such as creating the cocoon . They also have many cerebral organs that connect t the central nerve. Leeches have a somewhat different nervous system; their nervous system contains many optic nerve cords running along the body where it's transmitting information from their many (at least 10) eyes. It's nervous system also is in charge of maintaining it's hematophagous system, the same system used to suck blood from a host.
MY THOUGHTS
I learned that Charles Darwin studied worms. It is interesting that hey breathe through their skin, and can detect light and vibration, even though they do not have eyes. Finally, it is also interesting that some parasitic annelids have pouches along the digestive tract that hold enough food to last for months.