Vocabulary List Crop Gizzard Nephridia Setae Clitellum Metamerism Parapodia Tagmatization.

Vocabulary ListCrop GizzardNephridiaSetaeClitellumMetamerismParapodiaTagmatization

Phylum Annelida

Chapter 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!

Rep

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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 directions

2. Clitellum of one lines up with genital segments of other

3. 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.

Leeches

External 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