Vocabulary ListCrop GizzardNephridiaSetaeClitellumMetamerismParapodiaTagmatization
Phylum AnnelidaChapter 13
Characteristics of Phylum Annelida
Body is metameric (segmented arrangement of body parts)
Bilateral symmetry and wormlikeClosed circulatory systemIncludes over 10,000 species of
segmented worms-most are marineTriploblastic Coelomates
Characteristics of Phylum Annelida
Live everywhere except in frozen soil of polar regions and in the sand of dry deserts
Include earthworms, marine worms, and parasitic leeches
Different from flatworms and roundworms because they are segmented and have a coelom
Taxonomy of Annelida:
Kingdom AnimaliaPhylum Annelida
Class PolychaetaClass Clitellata
Class ClitellataCharacteristics:
Clitellum in cocoon formationMonoeciousFew or no setae
Two subclasses:Oligochaeta (earthworms)Hirudinea (leeches)
Subclass Oligochaeta
Over 3,000 species
Habitat: Freshwater Few estuarine Some marine Terrestrial
live in soil during hot weather,
may burrow 3 meters down
Lumbricus terrestris
EarthwormNo parapodiaCuticle covers bodyBody segmented with
short setaeClitellum:
Swollen set of segments in the anterior half
Will secrete mucus during copulation
Forms a cocoon
Subclass HirudineaLeechesAbout 500 species Most are freshwaterPredators of small
invertebratesFeed on body fluids
of vertebrates (parasites)
Class PolychaetaLargest class
(more than 5,300 species)
Mostly marineHabitat:
ocean floor Under rocks, shells Crevices of coral
reefs Burrow through
substrate (tubeworms)
Segments with extensions called parapodia
Numerous setae (bristles)First body segment called the
peristomium: has mouth, protomium, sensory tentacles (cirri) & 2
to 4 pairs of eyesMay be predators, herbivore, scavengers,
or filter-feeders
Metamerism & Tagmatization Segmental arrangement
of body parts in an animal.
It influences every aspect of annelid structure & function
The compartmentalization of the body has resulted in each segment having its own excretory, nervous, and circulatory structures.
The specialization of body regions in a metameric animal.
Although it is best developed in the arthropods, some annelids also display tagmatization.
Greek “tagma” means arrangement
Advantages of Metamerism (segmentation)Creation of hydrostatic compartments
Lessens the impact of injury
Permits the modification of certain regions of the body for specialized functions, such as feeding, locomotion, and reproduction.
Feeding & DigestionRunning through all
earthworm segments from the mouth to the anus is the digestive tract (a tube in a tube)
Food and soil taken in by the mouth pass through the pharynx into the crop, where they are stored until they pass to the gizzard (gizzard is a muscular sac containing hard particles that help grind soil and food before they pass into the intestine).
Feeding & DigestionNutrients are
absorbed from the intestine
Undigested material passes out of the worm’s body through the anus
Parasitic annelids have pouches along the digestive tract that hold enough food to last for months!
Circulation
Closed circulatory system. Oxygen and nutrients move to various parts of their bodies through their blood vessels.
At the same time carbon dioxide and metabolic wastes are removed from the blood and excreted.
Some of the vessels at the anterior end, or head, are large and muscular and serve as hearts that pump the blood.
The blood moves toward the anterior end of the worm in the dorsal blood vessel and toward the posterior end in the ventral blood vessel.
An earthworm has five hearts that pump blood through its circulatory system!
Respiration & Excretion
Segmented worms have 2 nephridia in almost every segment.
Cellular waste products are collected in the nephridia and are transported in tubes through the coelom and out of the body.
Nephridia also function in maintaining homeostasis of body fluids of annelids, ensuring that the volume and composition of body fluids are kept constant.
Response to StimuliAnterior segments are modified for
sensing the environmentYou might have seen an earthworm
quickly withdraw into its burrow when you shine a flashlight on it or step close to it….these observations show that earthworms can detect both light and vibrations.
MovementWhen an earthworm moves, it contracts circular
muscles running around each segment.This squeezes the segment and causes the fluid in
the coelom to press outward like paste in a tube of toothpaste being squeezed.
Because the fluid in the coelom is confined by the tissues between segments, the fluid pressure causes the segment to get longer and thinner…
Next, the earthworm contracts the longitudinal muscles that run the length of its body.
This causes the segment to shorten and return to its original shape, pulling its posterior end forward and resulting in movement!
MovementMany annelids have setae on each segment.
Setae are tiny bristles that push into the soil and anchor the worm during movement.
By anchoring some segments and retracting others, earthworms can move their bodies forward and backward segment by segment!
Repr
oduc
tion
Annelids can reproduce both sexually and asexually.
Most annelids have separate sexes, but some, such as earthworms and leeches, are hermaphrodites. Sperm are passed between two worms near segments
called clitellum (a thickened band of segments). It produces a cocoon from which young earthworms
hatch. Sperm and egg pass into the cocoon as it slips forward
off the body of the worm. After fertilization, the young are protected in the
cocoon as they develop.Some annelids reproduce asexually by
fragmentation.If a worm breaks apart, the missing parts
can be regenerated.
Earthworm reproduction
Monoecious & Exchange sperm 1. Copulation: Two worms line up in opposite
directions2. Clitellum of one lines up with genital segments of
other3. Mucus holds worms together4. Sperm travel from one to the other5. Last 2-3 hours6. After copulation, a cocoon is formed around worm7. Mucus, food, eggs and sperm are deposited in the
cocoon8. Fertilization occurs in the cocoon9. Worms back out of the cocoon and it drops to the
ground10. Hatching – takes a few weeks
Earthworms
Probably the best known annelidsUsed as bait for fishing and are found in
garden soil.Can eat its own mass in soil every day!Earthworms ingest soil to extract nutrients…
in this way, earthworms aerate the soil-they break it up to allow air and water to move through it (my mom always said, you know you’ve got good dirt if you find a worm)
Marine Annelids
Include bristleworms and fan worms
Have head regions with well-developed sense organs, including eyes.
Most body segments also have a pair of appendages called parapodia that are used for swimming and crawling
Fan worms are sessile and filter feeders, they trap food in the mucus on their fan-shaped structures.
If there is a threat nearby, fan worms retreat into their tubes.
LeechesExternal parasitesFlattened bodies and usually no setaeMost live in freshwater streams or rivers where
they attach to the bodies of their hosts-including fishes, turtles, and humans.
Leeches attach to their hosts using front and rear suckers.
When a leech bites, it saliva contains chemicals that act as an anesthetic.
Other chemicals in the saliva reduce swelling and prevent the host’s blood from clotting.
They maintain blood flow after microsurgery.
Medicinal leecheshttp://video.nationalgeographic.com/video
/player/places/countries-places/india/india_leechescure.html
http://www.leeches.biz/medicine-leech.htm
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