Earthworm

Pheretima is an earthworm. Earthworms feed on decaying fallen leaves and the organic matter mixed with soil.
They are detritivores and pass the soil through their gut, which improves soil fertility.

The clitellum is the glandular band covering segments 14–16 of the mature earthworm; its gland cells secrete the cocoon in which the sperms and eggs are deposited and fertilisation takes place. This match is correct.
Setae are S-shaped structures in the body wall that help in locomotion, not defence.
The typhlosole is the internal median fold of the dorsal wall of the intestine that increases the effective area of absorption; it does not store nutrients.
The gizzard (segments 8–9) is muscular and grinds soil particles and decaying leaves; it does not absorb food.
Hence the correct match is clitellum – secretes cocoon.

A characteristic feature of the intestine of the earthworm, after the 26th segment, is an internal median fold of the dorsal wall called the typhlosole.
The typhlosole increases the effective area of absorption in the intestine. This statement is correct.
The earthworm has a closed circulatory system with blood vessels and lateral hearts in segments; a long dorsal tubular heart is a feature of the cockroach.
Fertilisation and development take place outside the body, within the cocoon deposited in the soil.
The S-shaped setae help in locomotion, not in defence.
Hence the special feature is the typhlosole that increases the absorptive area of the intestine.

The body wall of the earthworm encloses a true body cavity, the coelom, which surrounds the gut and is filled with coelomic fluid.
If the body wall is pierced without damaging the gut, the needle enters the coelom, and the coelomic fluid oozes out.
The earthworm has a closed blood vascular system, so its blood is confined to vessels; it has no haemolymph (haemolymph is the fluid of the open circulatory system of arthropods).
Mucus is secreted on the surface and does not come out of a puncture.
Hence the fluid that comes out is coelomic fluid.

The earthworm is hermaphrodite. It has two pairs of testes, present in the 10th and 11th segments. This statement is correct.
The two pairs of accessory glands are present one pair each in the 17th and 19th segments, not in segments 16–18.
The four pairs of spermathecae are located in the 6th to 9th segments (one pair in each), not in segments 4–7.
The one pair of ovaries is attached at the intersegmental septum of the 12th and 13th segments, not the 14th and 15th.
Hence the correct description is two pairs of testes in the 10th and 11th segments.

Earthworms have no hard skeleton.
Their body cavity is a true coelom, filled with coelomic fluid and divided into compartments by septa.
The coelomic fluid is incompressible. When the circular and longitudinal muscles of the body wall contract against it, the fluid pressure makes the body segments stiff and turgid.
During burrowing the anterior end becomes turgid in this way and can be pushed into the soil; the fluid thus acts as a hydraulic (hydrostatic) skeleton.
Setae only provide a grip on the soil during locomotion, gut peristalsis moves food, and blood flows in a closed system of vessels; none of these gives turgidity to the body.
So the hydraulic skeleton is due to the coelomic fluid.