![]() ![]() The Euhirudinea is further divided into two orders: Acanthobdellida: a small northern hemisphere infraclass ectoparasitic on salmoniid fish, which lack an anterior sucker and retain chaetae.Euhirudinea: the 'true' leeches – marine, freshwater and terrestrial – which have suckers at both ends and lack chaetae (bristles).These are divided into two major infraclasses There are around 500 species of leeches world wide. Some species are considered amphibious as they have been observed in both terrestrial and aquatic habitats. Within ten minutes of sprinkling with a few drops of water, these leeches emerge, fully active.įreshwater leeches prefer to live in still or slowly flowing waters, but specimens have been collected from fast flowing streams. In these conditions the body is contracted dry and rigid, the suckers not distinguishable, and the skin completely dry. In dry weather, some species burrow in the soil where they can survive for many months even in a total lack of environmental water. Most do not enter water and cannot swim, but can survive periods of immersion. In drier forests they may be found on the ground in seepage moistened places. Land leeches are common on the ground or in low foliage in wet rain forests. Most leeches are freshwater animals, but many terrestrial and marine species occur. The Australian land leech has only two jaws and makes a V-shaped incision. Leeches usually have three jaws and make a Y-shaped incision. Unlike other annelids, leeches do not have parapodia ('feet') or chaetae (bristles) (except for Acanthobdellida). The anus is on the dorsal surface (top) just in front of the rear sucker.Įuhirudinea ('true' leeches) have 32 internal segments when mature and Acanthobdellida (a small group of fish leeches) have 29, but counting is difficult because four to six segments are included in an front sucker and seven in a rear sucker, while the remaining segments are secondarily annulated (ringed) to give two to five apparent segments per internal septum (internal membrane). The body tapers towards the head and has a small oral sucker surrounding the mouth and a larger caudal (tail) sucker at the rear end, except the marine fish parasites, Pisciolidae, which have a larger oral sucker. Most can vary considerably in shape both between the elongated and contracted state and between the starved and full condition. Some leeches are long and worm-like, others pear-shaped and broad. Usually they are dorso-ventrally (front to back) flattened and segmented, though the segments are not often seen. Leeches are bilaterally symmetrical, with thick muscular bodies. Instead, it only becomes visible during the breeding season. However, unlike the oligochaetes, leeches do not show the clitellum all year. They belong to the Class Clitellata (along with earthworms, Subclass Oligochaeta) because of the presence of a clitellum, which is a swelling towards the head of the animal, where the gonads are located. Leeches are segmented worms in the Subclass Hirudinea that are usually ectoparasitic. Thus, there was a comparatively large effect of leech predation on newly-hatched snails, due to a high probability of encounter and high predation rates, but spatial and temporal refuges probably reduce the importance of leech predation as a structuring force in freshwater snail assemblages.įunctional response Habitat complexity Leech Predation Snail.Leeches are annelids or segmented worms, and although closely related to the earthworms, are anatomically and behaviourally more specialised. complanata, which probably reduced encounter rates. Sandy substrates and greater snail size resulted in decreased predation rates. Predation rates were higher when leeches were feeding onLymnaea emarginata than onPhysa gyrina, whereas there was no significant difference in predation rates when they were feeding onL. Number of snails eaten increased with increasing density resulting in a type II functional response curve. complanata feeding on newly-hatched and juvenile snails was affected by snail species, snail size, snail density and substrate, in a laboratory experiment. ![]() In this study I investigated how predation rates ofG. The leechGlossiphonia complanata does not appear to have substantial impact on snail populations, but this may be due to most studies focusing on adult snails rather than juvenile snails. ![]()
0 Comments
Leave a Reply. |