Structure life cycle and parasitic adaptation of Hirudinaria granulosa

Structures of Hirudinaria granulosa.

External morphology:

1. Shape and size:The body of Hirudinaria is soft,vermiform, elongated, bilaterally symmetrical and metamerically segmented measuring about 10-15 cm and sometimes up to35 cm, The body is dorsoventrally flattened. The body is broadest near the posterior end, while narrowest near the anterior end.

2.Coloration:The dorsal surface is generally olive-green and the ventral surface is orange-yellow or orange-red and the two sides bear distinct stripes of orange or yellow and black. On the dorsal side is a median longitudinal black stripe.

3. Segmentation:The body of the leech is divided metamerically into segments, they always have 33 segments.In case, of leech, external segmentation does not correspond with the internal segmentation. Each segment is broken up externally by grooves into rings called annuli. The 1st and 2nd segments have one annulus each, 3rd has two annuli, 4th- 6th have three annuli each, 7th-22nd are broad heaving five annuli each, 23rd-26th have two annuli each, 27th-33rd have one annulus, they form posterior sucker. Each annulus of a segment is divided into small rectangular areas by longitudinal wrinkles.Each such area has a sort of papilla-like structure bearing sensory organ called annular receptor: there are 18 such receptors both on the dorsal and ventral surfaces of each annulus,Besides these, firs, annulus of each segment bears larger sensory organ called segmented receptors:these are 4 pairs on the dorsal side and 3 on the ventral side.

4.Suckers:Each end of the body bears a hollow muscular organ, the sucker.

a) Anterior sucker: Anterior or cephalic sucker comprises, the prostomium and three anterior body-sometimes. It is oval in outline with a ventrally directed, cuplike hollow, called the pre-oral chamber, at the bottom of which lies the mouth.

b). Posterior sucker: Posterior end of the body, also bears a circular and highly muscular disc, the posterior or anal sucker, also directed downwards . It is formed by the complete fusion of the last seven body segments (27 to 33) arranged in concentric rings.

5. Clitellum:During breeding season a girdle-like clitellum is formed around segments 9 to 11, rest of the year there is no clitellum.

6.Eyes:on the dorsal side are five pairs of eyes, one pair on each of the first and second segments, and one pair on the first annulus of the segment third, fourth and fifth. They are photosensitive in nature.

External apertures:

The external aperture of the body is as follows.

1. Mouth: It is a narrow triradiate aperture situated in the center of the funnel- like pre-oral,chamber of the anterior sucker.

2. Anus:It is very small aperture situated mid-dorsally on the 26 segment at the root of the posterior sucker.

3. Nephridiopore:There are seventeen pairs of nephridiopore lying on the ventral surface of the body, which one pair lies on the last annulus of each of the segments from 6th to 22nd.

4. Male genital pore: It is situated in a groove between the second and third annuli of the ten segment on the mid-ventral line of the body.A filamentous penis is sometimes seen protruding through this aperture.

6. Female genital pore;

It is usually smaller and less conspicuous than the male aperture.It is situated and mid-ventrally in a groove between the second and third annuli of the eleventh somite of the body.

Division of the body:

The body of leech is composed of 33 somites and is divided into following six regions:

1.Cephalic or head region:

It is composed of the first five segments.It includes the prostomium ,anterior sucker,the mouth and the eyes.A pair of eyes is situated on the dorsal side of the annulus in all cephalic segments.Thus, these segments are also referred as ocular segments.

2. Precliteller region:

It includes three segments,I,e VI, VII,and VIII all bearing nephridiopore.

3. Clitellar region:It is composed of three complete segments, I,e IX, X, and XI.There is not permanent clitellum but tempory clitellum develops only during breeding season. Nephridispores are also present in this region, the male and the female generative apertures are situated mid-ventrally on the X and Xi segments respectively.

4. Middle region:

It is the largest region of the body and consists of eleven complete somites (XII to XXII). It possesses nephridiopore.

5. Caudal region:This region is short and consists of four incomplete somites, I,e XXIII, XXVI. Segments XXVI bears the anal aperture on the dorsal side. There are no nephridiopore.

6. Posterior sucker:It is composed of segments (XXVII to XXXIII) arranged in concentric rings and each represented by single, annulus.These seven segments are completely fused and their intersegmental furrows are greatly suppressed.

Life-cycle and development of leech:

The life cycle of leech consists of copulation, fertilization, cocoon formation, and development which is summarized as below.

i) Copulation: Copulation of leeches, which possess a penis, is similar to direct transmission of sperms, as seen in earthworms.Copulation takes place during March and April. Two leeches come in contact with their ventral surfaces in head to the tail position, so that the male genital pore of one lies against the female genital pore of other.Penis of one leech enters the female genital pore of other and there is a mutual exchange of seminal fluid containing spermatophores, which enter the vagina of both the leeches. Copulation lasts for an hour after which the mates separate

ii)Fertilization:

Internal fertilization takes place in the vagina of each individual and the fertilized ova are discharged into a cocoon for further development.

iii) Cocoon formation:

Cocoons are formed the following copulation,during April, May, and June. The cocoon or ootheca or egg case is secreted in the form of a snow-white frothy girdle by the clitellum gland around segments 9,10,11. Clitellar glands also secrete an albuminous fluid which is deposited, with the fertilized ova.inside cocoon . The cocoon is then passed over the head of each individual.As the leech withdraws its anterior end by rhythmic movements, the prostomial glands secrete the two polar plugs of the cocoon .Complete cocoon is formed in about 6 hours, After which it is laid in a moist place by the side of a pond or pool,but never in water.It becomes hardened on exposure to air.

A well-formed cocoon is a light yellow or amber coloured barrel-shaped structure, about 25 to 30 mm long and 12 to 15 mm in diameter.Its wall consists of an inner thin tough membranous layer and an outer thick spongy layer. There is a distinct polar plug with a conical projection at each narrow end.

v) Development :Development of young proceeds within the cocoon. In each cocoon, 1-24 embryos develop and swim in the cocoon feeding on albumen,then finally escape from the cocoon. Development is direct.there is no larva, and it is completed in about 14 days.

Parasitic adaptation of leeches;

Hirudineria, the common Indian cattle each , leads a parasitic life as it feeds on the blood of cattle and man.For parasitics mode of life, there are a number of adaptive features in it. some of the parasitic adaptation is discussed as below.

• It's long, flattened, limbless swift swimming nature and slimy body are well suited for aquatic life.
• It's slimy body.covering protects it from desiccation: reduce friction in water during locomotory activity and also facilitates respiration through the skin.
• Its preference to live in a hollow water of the pond, tank lake and streams ensures food as the cattle and man frequently visit their water resources for drinking or bathing. It also provided concealment under weeds,logs, and stones at the bank of these resources.
• The three jaws are specialized weapons for inflicting a painless triradiate wound on the host's skin for sucking blood.
• Salivary gland of leeches secret an anticoagulating substance, called hirudin or anti-coagulin.
• These are well developed and provide the animal with greater opportunities of life.
• It takes place within the cocoon which serves as a protective covering. Further, development is quick and completed within a fortnight to ensure the maintenance of regular population.
• This double the rate of reproduction as, after copulation, both individual lay eggs.
• Anterior and posterior suckers are the organ of attachment: the Particular posterior sucker is much more powerful and muscular.
• It's well-developed receptor provide the better chance and survival.
• A short span of development period I,e fortnight and formation of several (up to 24) individuals in a cocoon ensures to maintain its regular population.

Reference:

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