Download File - MR. Hill`s class

Phylum Annelida
Latin for “Little rings”
Segmented Worms
Segmentation

Repeating, specialized sections for
different purposes or functions

Coelom is divided into separate
compartments by partitions

Septa

Enables different compartments to
contract or expand independently

Duplication of some of the organ
systems between each segment
provides insurance against injury
Taxonomy

Class Polychaeta


Class Hirudinea


many bristles
leeches
Class Oligochaeta

earthworms
Class Polychaeta - “many bristles”



Mostly marine worms
Have paddle-like appendages on sides
 “parapodia”
 Used for movement and respiration
Some have bristles to aid in defense
Bristleworm – many setae
Class Polychaeta

Have antennae


Sense the environment
Have specialized mouthparts for feeding
 Jaws (free swimming predators)
Class Polychaeta

Some free living



E.g. Nereis
Predatory
Some are sessile


live in tubes made of calcium,
silica (sand) or protein
Filter feeders
Class Hirudinea


Smallest class of Annelids (~300 species)
Leeches



Suck vertebrate blood
Carnivorous
Powerful suckers at both front and back ends
Leeches

No setae or parapodia


Have suckers at anterior and posterior ends
Move by “looping”:


Attach anterior sucker then pull rest of body forward
Classified as a parasite



Secrete an anaesthetic that prevents the host
from feeling their presence
Secrete an anti-clotting agent
If undisturbed, a leech can ingest 10 times its own
weight in blood
Class Oligochaeta

Earthworms



Found in soil and freshwater
Some types are found in the
ocean
Tubifex (sludgeworm)

Can survive in polluted
sediments, areas with little
oxygen
Oligochaeta anatomy
Oligochaeta anatomy
Movement

Requires coordinated movement between the circular and
longitudinal muscles

To move, the worm:
 anchors middle segments using setae
 contracts circular muscles in front of the anchored segments
 this “squeezes” the fluid in the coelom which in turn causes
the worm to “stretch” forward
 the worm then anchors the anterior end, releases the middle
and uses the longitudinal muscles to pull forward the
posterior end

Made possible by segmentation
Movement
Feeding and Digestion

Ingest soil as they burrow

Prostomium – flap of skin that covers the mouth when not
feeding
Mouth – where soil enters the worm
Pharynx – muscular region that forces soil through esophagus
into the crop



Crop – serves as temporary storage

Gizzard – muscular “blender” that grinds soil and organic
matter
Feeding and Digestion

Intestine – long “tube” that absorbs any nutrients
in the ground-up soil


has a special fold called a Typhlosole
 increases the surface area of the intestine
so that nutrients can be absorbed more
efficiently
Anus – where any undigested material exits the
worm = “worm manure”
Feeding and Ecology

Earthworms are decomposers
 Breakdown organic matter and
 Release nutrients into soil , thus fertilize it

Loosen soil as they burrow and

Aerate it (increase its oxygen content)
Feeding and Digestion
prostomiumm
Circulation

Closed circulatory system
 transports oxygen, carbon dioxide, nutrients and wastes
through the body of the earthworm

Ventral and Dorsal blood vessels

Blood is forced through blood vessel by contraction of vessels
and 5 aortic arches
Circulation
Respiration

No specialized respiratory organs

Oxygen and Carbon dioxide diffuse directly
through skin and into small blood vessels

Only if skin is moist
Excretion

Nephridia or Nephrostome act like kidneys


remove waste and control water levels in blood
Nephridiopores



pores on ventral side of worrm
release waste and excess water
each segment except first three and last one have nephridia
and nephridiopores
Excretion
Nervous System

Chain of ganglia connected by a ventral
nerve cord

Most body segments have a single ganglion

Have an anterior cerebral ganglia (brain!)

Can respond to light, touch, chemicals, moisture,
temp, vibrations
Nervous System
Reproduction

Hermaphroditic

individual worm
cannot fertilize own
eggs
Reproduction




The “Position”
 head to tail, ventral surface to ventral surface
The “Transfer”
 clitellum secretes mucus
 each earthworm injects sperm into the mucus
 mucus moves into pouch-like seminal receptacle of
each worm
The “Delivery”
 several days later the worm secretes a tube of mucus
and chitin (thick carbohydrate) from clitellum
 as the worm moves the tube “picks” up eggs and
carries it to sperm to be fertilized
The “Result”
 tube closes up to form protective case and 2-3 weeks
“baby” worms hatch
Review