Leech Circulatory System

Leeches are annelids that constitute the subclass Hirudinea. Almost all leeches are ectoparasites that attach to the host’s external surface. Like most other annelids, they also have an open circulatory system. Here, let’s learn more about the circulatory system of leeches.

Table of Contents

Leech – General Description

Most leeches are freshwater, but some are marine or terrestrial in nature. They are ectoparasitic, blood-sucking, or carnivorous in general. They are hermaphrodites showing sexual reproduction.

Their body is more elongated, cylindrical or dorso-ventrally flattened. The body has no setae or parapodia. Most leeches have suckers at both the posterior and anterior ends. They also have 33 segmentations (somites), and these segmentations are concealed by external ring-like markings called annulations. The annuli are divided by transverse separation walls called septa. Also the number of annuli varies in each segment of the leech. Annular receptors can be found in each annulus, while segmental receptors can be found on the 1st annulus of each segment. Each annelid segment contains nervous, excretory, and circulatory system units.

Also Check: Diagram of Leech (Hirudinaria granulosa)

Leech

Leech Circulatory System

Leeches show an open circulatory system. They transport gases across their body walls. Some leeches retain the basic circulatory pattern of Annelida, but it is highly modified in most leeches, with coelomic channels replacing vessels. Coelomic fluid has replaced blood, and respiratory pigments are absent except in two orders.

The haemocoelomic system of leeches is made up of coelomic channels. Coelomic channels are filled with a type of blood-like fluid and these channels represent the blood vessels. Haemoglobin is found in coelomic fluid. These channels are used to circulate colourless corpuscles. There are four such channels that make up the haemocoelomic system:

  • One ventral channel – It runs mid-ventrally below the alimentary canal from one end to the other end of the body. Here, the fluid flows from the anterior to the posterior end.
  • One dorsal channel – It runs mid-dorsally above the alimentary canal. Both dorsal and ventral channels are devoid of valves.
  • Two lateral channels – These 2 channels are present on either side of the leech’s alimentary canal. They are valvular and muscular. In the dorsal and 2 lateral channels, the haemocoelomic fluid flows from behind to forward.

All these 4 channels are posteriorly connected together at the 26th segment.

Keep exploring BYJU’S Biology to learn more such exciting topics.

See more:

Difference between Leeches and Bloodsuckers

Difference between Open and Closed Circulatory Systems

Difference between Worms and Parasites

Frequently Asked Questions

Q1

Where are leeches found?

Leeches are sanguivorous animals that feed on the blood of frogs, fish, humans and cattle. It can be found in freshwater ponds, swamps, lakes, and slow-flowing streams. The Indian cattle leeches are cosmopolitan in distribution and are mostly found in Bangladesh, India, Pakistan, Sri Lanka and Myanmar.
Q2

What are open and closed circulatory systems?

Most animals have a closed circulatory system, which means that blood is contained within vessels throughout the body, whereas others like leeches have an open type of circulatory system, which means that blood is not contained within vessels.
Q3

What is hirudin?

Hirudin is a naturally occurring peptide with anticoagulant properties found in the salivary glands of blood-sucking leeches. These anticoagulants prevent their host’s blood from clotting or coagulating.
Q4

What is the function of suckers in leeches?

Leeches possess 2 suckers. The sucker at the anterior end is called the oral sucker, and it occupies the first 5 segments. Whereas the last 7 segments fuse to form the posterior sucker. The anterior sucker helps with feeding, and both posterior and anterior suckers help with attachment and locomotion.