EARTHWORM NOTES CLASS 11 | MORPHOLOGY AND ITS ANATOMY

The basic tissues mentioned above organise to form organs which in turn associate to form organ systems in the multicellular organisms.

EARTHWORM

Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper layer of the moist soil.
common Indian earthworms are Pheretima and Lumbricus.
live in burrows made by boring and swallowing the soil.

Earthworms have long cylindrical body.
Body is divided into more than hundred short segments
.The prostomium is sensory in function.
Anterior end consists of the mouth and the prostomium, a lobe which serves as a covering for the mouth
A single female genital pore is present in the mid-ventral line of 14th segment.
A pair of male genital pores are present on the ventro-lateral sides of the 18th segment.

The body wall of the earthworm is covered externally by a thin non-cellular cuticle.
The alimentary canal is a straight tube and runs between first to last segment of the body.
A terminal mouth opens into the buccal cavity (1-3 segments) which leads into muscular pharynx.
A small narrow tube, oesophagus (5-7 segments), continues into a muscular gizzard (8-9 segments).
It helps in grinding the soil particles and decaying leaves, etc.
The stomach extends from 9-14 segments.
Calciferous glands, present in the stomach, neutralise the humic acid present in humus.
Intestine starts from the 15th segment onwards and continues till the last segment.
A pair of short and conical intestinal caecae project from the intestine on the 26th segment.
The characteristic feature of the intestine after 26th segment except the last 23rd-25th segments is the presence of internal median fold of dorsal wall called typhlosole.
This increases the effective area of absorption in the intestine.
The alimentary canal opens to the exterior by a small rounded aperture called anus
The ingested organic rich soil passes through the digestive tract where digestive enzymes breakdown complex food into smaller absorbable units.
These simpler molecules are absorbed through intestinal membranes and are utilised.

Pheretima exhibits a closed type of blood vascular system, consisting of blood vessels, capillaries and heart.
. Due to closed circulatory system, blood is confined to the heart and blood vessels.
Contractions keep blood circulating in one direction. Smaller blood vessels supply the gut, nerve cord, and the body wall. Blood glands are present on the 4 th, 5th and 6th segments.
They produce blood cells and haemoglobin which is dissolved in blood plasma.
Blood cells are phagocytic in nature.
Earthworms lack specialised breathing devices.
Respiratory exchange occurs through moist body surface into their blood stream.