Annelida

Segmented Worms

N0- not that kind of worm!

Common Examples

• Earthworms

Common Examples

• Bristle Worms

Common Examples

• Feather Duster Worms

Common Examples

• Tube Worms

Common Examples

• Tube Worms

Common Examples

• Leeches

• Rag Worm

How would

you like to run

into the jaws of

this guy!

Characteristics

• Segmentation• Cephalization• Bilateral Symmetry• Coelomates• One way digestive tract• Both Filter Feeders and Predators• Asexual and Sexual Reproduction• Water and Land Examples

Segmentation

•Each segment repeats •Very efficient design. •Some are specialized

•Digestion, reproduction,excretion, etc.

Definite Head End

Annelida has Bilateral Symmetry

Yes,Symmetric

No, notSymmetric

No, notSymmetric

• The basic body plan = a tube within a tube• internal tube=

suspended w/in coelom = digestive tract.

Body StructureBody Structure

Phylum Annelida• Hydrostatic skeleton

– Fluid pressure in coelom provides support & locomotion

– Circular muscles

– Longitudinal muscles

– Peristaltic locomotion – squeeze, relax, squeeze!

• SETAE = tiny bristles on each segment

• help move

• anchors body in soil so each segment can move the animal along

Setae

Body StructureBody Structure

Phylum Annelida• Setae (“bristles”) of chitin – a carbohydrate

• Chitin forms the exoskeleton in insects, shrimp, crayfish, etc.

– “anchors” for earthworm

– “paddles” for polychaete

– Enlarged as jaws in leeches, some polychaetes

• distinguishing characteristic is that bodies are divided into ringed segments

• In most species, segmentation continues internally as each segment is separated from the others by a body partition.

Body StructureBody Structure

Segments

• Each segment has its own muscles, allowing shortening and lengthening of the body.

• Segmentation also allows for specialization of body tissues.

• Certain segments have modifications for functions such as sensing and reproduction.

Body StructureBody Structure

• Segmented worms have simple nervous systems in which organs in anterior segments have become modified for sensing the environment = cephalization

Nervous systemNervous system

• Some sensory organs are sensitive to light, and eyes with lenses and retinas have evolved in certain species.

• In some species there is a brain located in an anterior segment.

• Nerve cords connect the brain to nerve centers called ganglia, located in each segment.

Setae

Brain

Nervous systemNervous system

Phylum Annelida• Closed circulatory system

– Multiple “hearts”– Hemoglobin not in blood cells

• reddish-pink color• Blood carries O2 to and CO2

from body cells

• flow through vessels to reach all parts of the body

• must live in water or in wet areas on land because they exchange gases directly through their moist skin – like your lungs

• complete internal digestive tract

• length of body

• Nutrients diffuse to blood

• Transported to all cells

Digestion and ExcretionDigestion and Excretion

• Food > mouth > crop >gizzard > gut >anus

• GIZZARD

• a muscular sac

• Contains hard particles to grind soil and food before they pass into intestine/gut

Mouth

Crop GizzardDigestion and ExcretionDigestion and Excretion

Circulatory System

• have two nephridia in almost every segment.

• Special cells that collect waste and transport it through the coelom and out of the body.

Nephridia

ExcretionExcretion

• Earthworms and leeches are hermaphroditic

– exchange sperm.

• forms a capsule for the eggs and sperm.

• The eggs fertilized in capsule, then it slips off the worm and left in soil

• 2-3 weeks, young worms emerge from the eggs.

ReproductionReproduction

• separate sexes and reproduce sexually.

Reproduction in BristlewormsReproduction in Bristleworms

• eggs and sperm are released into seawater and fertilize there = external fertilizaton

• larvae hatch in sea

• become part of the plankton –important part of food chain

• Eventually settles to the bottom to live

• ClassOligochaeta - earthworms

• Class Polychaeta - bristleworms

• Class Hirudinea - leeches

CLASSES OF ANNELIDACLASSES OF ANNELIDA

• most well-known annelids

• Easily seen by most people.

Class Oligochaeta: EarthwormsClass Oligochaeta: Earthworms

• burrows through soil

• Loosens and aerates soil

• Feces = “castings” = fertilizer

• Ecologically very important

• Possible human food source= protein

Class Polychaeta: BristlewormsClass Polychaeta: Bristleworms

• Polychaete means “many bristles”

• Most body segments have many setae

• has a head with well-developed sense organs, including eyes.

• have parapodia, (paired feet)

• can be used for swimming or crawling over corals and bottom of sea.

Class Polychaeta: BristlewormsClass Polychaeta: Bristleworms

• Parapodia also function in gas exchange.

• segmented worms with flattened bodies

• usually no setae

Class Hirudinea: LeechesClass Hirudinea: Leeches

• Many are parasites

• suck blood or other body fluids from hosts (ducks, turtles, fish, and humans).

• saliva contains:

– anesthetic chemicals

– Anticoagulants – prevent clotting of blood

• can ingest 2 to 5 times its weight in 1 meal.

Hirudinea: LeechesHirudinea: Leeches

• Front and rear suckers for attachment

• Annelids probably evolved in the sea, perhaps from larvae of ancestral flatworms.

Origins of Segmented WormsOrigins of Segmented Worms

•Tubes constructed by polychaetes are the most common fossils of this phylum.

•Some of these tubes appear in the fossil record as early as 540 million years ago.