CLASSIFICATION OF PHERETIMA : EARTHWORM
PHYLUM :- ANNELIDA (Metamerically segmented, coelomate and laterally symmetrical. )
CLASS :- OLIGOCHAETA (Few setae.)
ORDER :- NEO-OLIGOCHAETA (Modern and terrestrial forms.)
FAMILY :- MEGASCOLECIDAE (Large form family of earthworms)
GENUS :- Pheretima
Cosmopolitan. But mostly in New Guinea and parts of Southeast Asia
HABIT AND HABITAT
Pheretima is found in the soil but absent in sandy and humus deficient soil. They are found in mountains, clayey and acidic soils. They live usually in the upper layers of slightly damp soils, lawns, gardens and up to the depth of 30 to 45 cm in burrows for protection against enemies and under unfavourable condition. According to Darwin one acre of land may contain 63,000 earthworms. It is nocturnal. The earthworm is hermaphroditic (monoecious) .
GENERAL CHARACTERSTICS OF PHERETIMA : EARTHWORM
- Commonly called as Earthworm.
- Body consists of 100 to 120 ring like segments depicting true metamerism and measuring approximately 150 mm.
- Both external and internal segmentations are distinct. The worm is glistening deep brown or clay-coloured.
- Anterior end is somewhat narrowly pointed, while posterior end is bluntly pointed.
- Except the first and last segment, each segment contains a row of setae in the ventral body wall.
- Dorsal surface is dark brown in colour and it is easily recognized by dark median line of dorsal blood vessel.
- First segment is called as prostomium which contains ventral mouth. The last segments is called as anal segment containing anus.
- A portion of the body is thickened and is called as clitellum around 14 to 16 segments.
- Spermathecal pores are found in the inter-segmental grooves of 5/6, 6/7, 7/8 and 8/9 segments. The female genital pore on the 14th segment and male-genital pores on the 18th segment. Two pairs of genital papillae lie on the ventral surface in the 17th and 19th segments.
- Cross-fertilization, but copulation has not been studied in P. posthuma. Development takes place in cocoons.
Earthworm is economically very important as :-
- It is used as fishing bait.
- It has medicinal, educational and experimental value.
- The earthworms are beneficial to agriculture. They are important agent in the conditioning of soil and permit water to enter easily during rain. The constant mixing of soild and organic debris contributes to development of good humus. Earthworms are very good fertilizers and are cultured.
The Animal contains clitellum in 14 to 16 mm segments and all above features, hence, it is Pheretima.