7. STRUCTURAL
ORGANISATION IN ANIMALS
MORPHOLOGY & ANATOMY OF EARTHWORM
Systematic position
Phylum : Annelida
Class : Oligochaeta
Genus : Pheretima
Species : posthuma
· Earthworm is a reddish-brown terrestrial invertebrate
that inhabits the upper layer of moist soil.
· During day time, they live in burrows made by boring and
swallowing the soil.
· Common Indian earthworms: Pheretima and Lumbricus.
MORPHOLOGY OF EARTHWORM
·
Earthworms
have long segmented cylindrical body.
·
Number
of segments (metameres): about 100-120.
·
Dorsal surface has a dark median
mid dorsal line (dorsal blood vessel)
along the longitudinal axis of the body.
·
First
segment (peristomium or buccal segment)
bears the mouth. A lobe called prostomium
covers the mouth.
·
Prostomium
is sensory in function and is used to force open cracks in the soil into which
the earthworm may crawl.
·
In a
mature worm, segments 14-16 are
covered by a dark band of glandular tissue called clitellum.
·
Body
has 3 regions: preclitellar, clitellar & postclitellar.
·
4 pairs of spermathecal apertures are found on
ventro-lateral sides of intersegmental
grooves (5th -9th
segments).
·
A
single female genital pore is
present in the mid-ventral line of 14th
segment.
·
A
pair of male genital pores is
present on the ventro - lateral sides of the 18th segment.
·
Many
minute nephridiopores open on the
body surface.
· All segments except the first, last and clitellum bear S-shaped setae, embedded in the epidermal pits. Setae can be extended or retracted. Their function is locomotion.
