Earthworm important points

 

                             Earthworm

Important points

# The ventral surface of the body of the earthworm can be distinguished by the dorsal surface by the presence of genital openings or pores.

#The genital openings in the earthworm help in cross-fertilisation and pores help in removal of the wastes generated in the body.

# The body of the earthworm is divisible into three prominent regions-
i. Preclitellar segment
ii. Clitellar segment
iii. Postclitellar segment.

#The first body segment is called as the peristomium which contains the mouth.

# In a mature worm, segments 14-16 are covered by a prominent dark band of glandular tissue called the clitellum.

# Four pairs or eight spermathecal apertures are situated on the ventrolateral sides of the intersegmental grooves, i.e., 5-9 segments.

# A single female genital pore is present in the mid-ventral line of 14^th segment.

# In each body segment, except the first, last and clitellum, there are rows of S-shaped setae, embedded in the epidermal pits in the middle of each segment.

# Setae can be extended or retracted. Their principal role is in locomotion.

# The body wall of the earthworm is covered externally by a thin non – cellular cuticle below which is the epidermis, two muscle layers – circular and longitudinal and an innermost coelomic epithelium.

# The characteristic feature of the intestine of an earthworm is the presence of internal median fold of dorsal wall called typhlosole.

# Typhlosole helps in increasing the effective area of absorption for food and minerals. 

# Typhosole are present after the 26^th segment except for the last 23^rd-25^th segments.

# In earthworm, blood glands are present on the 4^th, 5^th and 6^th segments.

# Blood gland produce blood cells and haemoglobin which is directly dissolved in blood plasma as their blood does not have any respiratory pigment.

# The excretory organs of earthworm occurs as segmentally arranged coiled tubules called nephridia.

# Nephridia are of three types –
i. Septal nephridia
ii. Integumentary nephridia
iii. Pharyngeal nephridia.

# Nervous system of the earthworm is represented by ganglia arranged segment-wise on the ventral paired nerve cord.

# The nerve cord on the anterior region bifurcates, laterally encircling the pharynx and joins the cerebral ganglia dorsally to form a nerve ring.

#  Earthworm show  external and cross-fertilization.

# Fertilisation and development occur within the cocoons which are deposited in the soil.

# Development of earthworms is direct, i.e., there is no larva formation.

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