THE EARTHWORM

This page provides a summary of the main features of earthworms. In particular the classification refers to one of the common earthworms found in New Zealand. I plan to add diagrams and a glossary, check back later.

Classification:

Phylum	Annelids	- segmented worms
Class	Oligochaeta
Genus	Allolobophora
Species	caliginosa

Nutrition:

The earthworm feeds on organic matter in the soil and plant matter which it drags down into its burrow

 It uses it pharynx to suck food or soil into its mouth

The oesophageal glands add chalk to neutralise any acidity in the soil

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The crop temporarily stores the food
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The gizzard has a horny lining which helps grind up the food into smaller particles

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Food is absorbed in the intestine
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Undigested food passes out the anus and is deposited as 'worm casts'

Respiration and gas exchange:

The earthworm 'breaths' through its moist skin
Oxygen from the air dissolves in the moisture on the worms skin and then travels into the skin blood capillaries.
The haemoglobin in the blood carries the oxygen around the worms body
CO₂ is lost from the body by the opposite process - though CO₂ is not carried by the haemoglobin.

Blood system:

Earthworms have a closed circulatory system
Their blood contains red haemoglobin (in solution) to transport oxygen and white blood cells to fight infection
The blood is pumped around the body by 5 pseudohearts (they are like enlarged blood vessels)
The pseudohearts are located around the oesophagus

Nervous system:

Earthworms have no eyes, ears or nose
They can sense light and dark by small light sensitive cells found mainly on the uppers skin surface at the ends of their body
They sense vibrations and chemicals by the means of tiny touch or chemical sensitive cells
Each segment contains a ganglion - a swollen region of nerves which receives messages from that segment.
There is a cerebral ganglion (primitive brain) in segment 3 above the buccal cavity.
The worm will move away from light, vibrations and dangerous chemicals

Support and movement:

Earthworms have a hydrostatic (= fluid) skeleton
They move by squeezing the circular muscles of each segment to make their body extend forward, then they grip the surface with their bristles and contract their longitudinal muscles so their body is pulled up to their anterior (front) end
The above process can occur at several places along the body at the same time

Excretion:

CO₂ is excreted through the moist skin
Nitrogen containing waste (from protein breakdown) is removed by nephridia. These are long coiled tubes which remove nitrogen wastes from blood capillaries and excrete it through tiny pores on the skin surface
There are 2 nephridia in each segment

Reproduction:

Earthworms are hermaphrodites but they don't fertilise themselves
The worms lie side by side facing opposites directions. They secrete a mucus from their clitellums (= saddles), this hold the worms together. Sperm are released from segment 15 and they travel to the clitellum and into the spermathecae (=sperm storage sacs) on segment 9 and 10 of the other worm
Later the worm secretes a cocoon from its clitellum as it wiggles backwards out of the cocoon the worm releases 8-16 eggs and sperm from the spermathecae .
Usually only one worm hatches from the cocoon

Habitat, niche and environment:

The worms habitat is moist, humus rich soil. In dry weather it burrows deeper into the soil to avoid drying out
The worms niche is a herbivore and macro-decomposer. It is important as a source of food for birds. It also helps aerate the soil and helps increase soil fertility by manuring it with leaf litter
The worms environment is humid, moist and cool

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