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[leech.jpg]

Class Hirudinea

(Leeches)

Soil & Water Conservation Society of Metro Halifax (SWCSMH)

UpdAted: October 09, 2013      Freshwater Benthic Ecology and Aquatic Entomology Homepage


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Contents:



Introduction

The class Hirudinea in the phylum Annelida (segmented worms) comprises the leeches, the most highly specialized of the major annelid groups.

Leeches are typically dorsoventrally flattened annelids with suckers at both ends and 34 body segments (designated I-XXXIV) which are externally divided into a number of annuli. Most species in North America are found in fresh and marine waters, but many terrestrial species occur in tropical regions. As predators, parasites of animals, vectors of parasites, and as food for semiaquatic and aquatic animals, leeches are important components of food webs. In northeastern North America, there are about 42 species. Leeches are hermaphroditic but do not self-fertilize.

The class Hirudinea comprises two orders: Arhynchobdellida and Rhynchobdellida:


Habitat

Leeches are most common in warm, protected shallows where there is little disturbance from currents. Free-living leeches avoid light and generally hide and are active or inactive under stones or other inanimate objects, among aquatic plants, or in detr itus. Some species are most active at night.

Silted substrates are unsuitable for leeches because they cannot attach. Leeches are usually rare in calcium-poor waters. Some species can tolerate mild pollution.


Indicator value

Leeches are most common in warm, protected shallows where there is little disturbance from currents. Free-living leeches avoid light and generally hide and are active or inactive under stones or other inanimate objects, among aquatic plants, or in detritus. Some species are most active at night. Very rarely are leeches which attach to humans encountered in fast moving water or riffle areas. Many are scavengers or feed on other invertebrates. They are carnivorous, feeding mostly on insects, molluscs and oligochaetes, or scavengers, feeding on dead animal matter.


Micrograph of a leech:

[Img-leech2.jpg]



View: ventral


References and web URLs:




Freshwater Benthic Ecology and Aquatic Entomology Homepage                     Soil & Water Conservation Society of Metro Halifax (SWCSMH) Master Homepage


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