7 min readConcept sheetPart I (1 mark) and Part II (2 marks): segments, suckers and regions; Part III (4 marks) with a diagram

Leech: habitat and external features

The Indian cattle leech, Hirudinaria granulosa, is a blood-sucking annelid with a soft body of 33 segments, two suckers and six body regions.

ClassificationPhylum Annelida, Class Hirudinea

Segments33, each divided on the surface into rings (annuli)

SuckersAnterior (around the mouth) and posterior (larger)

Food habitSanguivorous (feeds on blood); an ectoparasite

Habitat and habits

The Indian cattle leech lives in freshwater ponds, lakes, swamps and slow streams. It is an ectoparasite: it lives on the outside of its host. It sucks the blood of cattle, fish, frogs and sometimes people who wade into the water. An animal that feeds on blood is called sanguivorous.

External features

The body is long, soft, worm-like and segmented. It is dorsally convex (curved on top) and ventrally flat.
Colour: olive green on the dorsal side and orange-red on the ventral side.
There are 33 segments. Each segment is divided on the surface into rings called annuli.
An anterior sucker surrounds the mouth at the front end. A larger, round posterior sucker lies on the ventral side of the hind end. Both help in attachment and movement.
Five pairs of eyes lie on the dorsal side of the first five segments.
The anus opens on the dorsal side of the 26th segment.
On the ventral side, the male genital pore is on the 10th segment and the female genital pore is on the 11th.
17 pairs of nephridiopores open on the ventral side of segments 6 to 22.
In the breeding season, segments 9, 10 and 11 form a girdle, the clitellum, which makes the cocoon.

Six regions of the body

Region	Segments	Feature
Cephalic (head) region	1 to 5	Eyes; anterior sucker with the mouth
Pre-clitellar region	6 to 8	First nephridiopores
Clitellar region	9 to 11	Clitellum; male (10th) and female (11th) genital pores
Middle region	12 to 22	Testes inside (one pair in each segment); nephridiopores outside
Caudal region	23 to 26	Anus on the dorsal side of the 26th segment
Posterior sucker	27 to 33	Seven segments fused to form the sucker

How a leech moves

Looping (crawling)The leech fixes its posterior sucker and stretches forward. It fixes the anterior sucker, then lets go of the posterior sucker and pulls the hind end up close, making a loop, like a caterpillar.

SwimmingIn water, it swims by wave-like (undulating) movements of its body, using its muscles.

Unlike the earthworm, the leech has no setae or parapodia. It moves with its suckers and muscles.

How to draw the external features of a leech

1
Draw a long, flat, leaf-like body, narrow at the front and wide at the back.
2
Draw many thin cross-lines for the annuli, and a few thicker lines to show segments.
3
At the front, draw a small cup: the anterior sucker with the mouth. On the dorsal view, mark the eyes (five pairs).
4
At the back, draw a large round disc: the posterior sucker. On the dorsal view, mark the anus just in front of it.
5
On the ventral view, mark the clitellum (9 to 11), the male genital pore (10), the female genital pore (11) and dots for nephridiopores.

In real life

Leeches are common in paddy fields and ponds, and trekkers in the Western Ghats often find them clinging to their legs during the monsoon.

Exam angle

1 marks: “How many segments does the body of a leech have?” 33.

2 marks: “Name the six regions of the body of a leech.” Cephalic, pre-clitellar, clitellar, middle, caudal and posterior sucker regions.

4 marks: “Describe the external features of a leech.” Shape and colour; 33 segments with annuli; two suckers; five pairs of eyes; six regions; openings (mouth, anus, genital pores, nephridiopores); clitellum.

Remember it

Leech regions: 'Cats Purr, Cows Moo, Crows Peck': Cephalic, Pre-clitellar, Clitellar, Middle, Caudal, Posterior sucker. Segments 5 + 3 + 3 + 11 + 4 + 7 = 33.