Annelids

Septa/Septum

Internal walls which seperate the segments

Setae

Small bristle-like structures found in earthworms which aid in locomotion and help the earthworm move through soil

Prostomoium

First, pre mouth segment on the earthworm located in front of the mouth

Mouth

Where food enters to be digested.

Pharynx and its function

1. A feeding organ, or, the muscular front section of the digestive tube in annelids

2. Sucks in food (various ways)

What is different about marine annelids from terrestial annelids in terms of the pharynx?

They are able to eject it, and have hooks on them.

Digestive tract

A long tube in annelids which extends from the mouth to the tip of the tail, or, the anus,

Parts of the digestive tract in order

1. Mouth

2. Pharynx

3. Esophagus

4. Crop

5. Gizzard

6. Intestine

7. Anus

Clitellum description

1. A thickened, glanudular, and non segmented section of an earthworm which plays a role in reproduction

How does the clitellum aid in fertilization?

It produces a mucus ring, which slides off, in which egg and sperm are released.

What does the mucus ring produced by the clitellum later become? Why?

A cocoon, which protects the fertilized eggs.

How do carnivorous annelids use their pharynx to feed?

Their pharynx has two or more sharp jaws which extend to hunt prey when the worm lunges forward.

How do herbivorous annelids use their pharynx to feed?

They have jaws which are used to tear apart algae.

How do some detritus feeders use their pharynx to feed?

Their extended pharynx is lined with sticky mucus, which presses against the sedimented floor to trap food. Once trapped, the pharynx returns to normal position and food enters the digestive tract.

How do other detritus feeders (ie earthworms) use their pharynx to feed?

They use their pharynx as a “pump” to suck detritus and soil and force it down their gut.

How do parasites use their pharynx to feed?

They use their pharynx by sucking blood and tissue fluid from their host.

What are two other feeding strategies/modifications annelids use?

1. Fanning water through tube like burrows, passively catching nutrients in mucus bag

2. Worms such as plume worms use featherlike structures which make up the firsts segments to sift detritus and plankton from water

How do awautic annelids usually breathe?

Using gills

What are 2 respiratory strategies/modifications in aquatic annelids?

1. Feather duster worms use their feathery gills which protude from their burrows to breathe.

2. Other aquatic worms use small delicate gills located on the sides of the body, and fan water through them.

What is the risk of annelids (terrestial) exchanging gases?

Exchanging gases requires moisture, which if lost, causes the worm to dry out, causing the worm to die.

What adaptation do terrestial annelids have to protect against moisture loss?

They secrete a thin protective coating known as a cuticle.

What are considered the “hearts” of an annelid?

The aortic arches.

What type of circulatory system do annelids have? Describe it as well.

A close circulatory system in which there is a heart, blood vessles, and blood.

How many “hearts” do annelids have?

5

Explain the direction of blood movement through blood vessels in annelids.

Blood flows to the head via the dorsal blood vessels, and then to the back of the body via the ventral blood vessels

Ring vessels

Any vessel which connects the dorsal and ventral vessels. Supply blood to internal organs.

What distinguishes a pumping ring vessel from a normal ring vessel

A pumping ring vessel has muscles and are bigger, ryhmatically pumping blood throughout and annelids system.

How do some other annelids pump blood throughout the body?

Through muscle contractions

What are two ways in which Annelids excrete?

1. Solid wastes out through anus

2. Metabolic wastes filtered out through nephridia

Where are nephridia located?

On each segment of the worms body

Where does the brain sit in an annelid?

Dorsal to the gut

What connects the brain to the pair of ganglia below the brain?

Two large nerves

What happens at each worm segment with the ventral nerve cord?

The nerves at each segment enter and leave the nerve cord at a pair of small ganglia

What sensory organs are observed in annelids?

Sensory tentacles, statocysts, Chemical receptors, and 2/2+ pairs of eyes

Function of sensory tentacle

• Used for “feeling” the environment

• Senses water flow, presence of chemicals, andphysicaly contact

Function of statocysts

Help with balance

Function of chemical receptors

Used for tasting and detect odours to locate food/avoid harmful susbtances

Function of 2/2+ pairs of eyes

For light detection. Some can discern simple shapes or patterns.

How do earthworms sense their world without sensory organs? What do they detect?

They use simple sensory cells instead located on their skin to detect light, chemicals, and vibrations

Provide 4 ways annelids evade predators

1. Rapidly burrowing/swimming away

2. Marine fanworms secrete calcium carbonate

3. Carnivorous use jaws

4. Marine fireworms which use tufts of poisnoinous bristles

Longitudianal muscles cause the worm to…

become shorter/longer

Circular muscles cause the worm to…

become skinner/fatter

How do marine annelids use the two muscle groups to move?

By “wriggling” through the water

How do terrestrial annelids use these two muscle groups to move?

To force their way through sediment.

How do annelids reproduce asexually? Is it common?

Through budding. Not common

Sexual reproduction 1

External fertilzation + seperate sexes

Sexual reprodcution 2

Internal fertilization + hermaphrodites

Steps in internal fertilization in annelids (6 steps)

1. Worms pair up

2. Attatch to each other

3. Exchange sperm

4. Each worm recieves sperm in a speical sac

5. Clitellum secretes mucus ring into which gametes are released

6. Once fertilization occurs, mucus ring becomes cocoon to house fertilized egg

2 characteristics that all worm phyla share

1. Bilateral symmetry

2. Tripoblastic layers

What are polychaeta characterized by?

paired paddlike appendages on their body segments