Question

One very special feature in earthworm (Pheretima) is that
A. Fertilization of egg occurs inside the body
B. The typhlosole greatly increases the ineffective absorption area of the digested food in the intestine
C. The S-shaped setae embedded in the integument are the defensive weapons used against the enemies
D. It has long dorsal tubular heart

Answer 1

Pheretima is a genus of earthworm species. They are burrowers found in the soil rich in decaying organic matter. Earthworms are known as farmer’s best friend. The rainy season is most favorable for earthworms.

Complete answer:
Earthworms are burrowers found in soils. They are very beneficial for the soil as they help in breaking down complex organic matter. They usually breed in the rainy season. They are poikilothermic (cold blooded) animals. They have a long, elongated, cylindrical narrow body which is bilaterally symmetrical. They have tapered anterior end whereas posterior end is more blunt. The earthworms have slimy bodies and are light to dark brown in color. They have pigment porphyrin present in their body which protects them from bright light.
They are hermaphrodite and reproduction is either sexual or parthenogenetic. They have a distinct, spacious coelom which contains coelomic fluid. Their body consists of a mouth, anus, female genital aperture, at the clitellar region; male genital aperture, spermathecal aperture, and nephridiopores.
The digestive system of Pheretima has a long alimentary canal which is held in position by inner septa. They have a typhlosole, an internal fold present in the intestine. It increases the ineffective absorption area of the digested food in the intestine. Respiration in earthworms is mainly carried out on their skin, which is richly supplied with blood vessels. If in case, the skin of earthworm becomes dry, it dies of asphyxia, as moist sin is important for gaseous exchange. Circulatory system of earthworms is formed by closed blood vessels. The blood is made up of hemoglobin which is in dissolved state and therefore is colorless. They have a well-developed nervous system having CNS, PNS and receptor organs.

Hence, the correct answer is option (B).

Note: Earthworms are beneficial for soil in many ways. They increase the nutrient amount in soil by taking part in the process of decomposition. They provide better drainage of water in soil. They also feed on plants and debris.