Segmented worms: Leeches

Code LH999999

Key terminates here

Class: Hirudinea

Annelids are segmented worms with a subterminal mouth, straight gut with or without diverticulae, posterior anus, dorsal pre-oral brain, paired ganglionated ventral nerve cords, a closed blood circulatory system (occasionally reduced or absent), a well-developed coelom divided by septa (corresponding to the external segmentation, except in leeches) and typically with moveable setae in bundles on most body segments.

Hirudinea (leeches) may be ectoparasitic or free-living. Most species occur in marine or freshwater habitats but a few are terrestrial. Leeches invariably have 34 internal segments when mature, but counting is difficult because 4-6 segments are included in an anterior sucker and 7 in a posterior sucker while the remaining segments are secondarily annulated to give 2-5 apparent segments per internal septum. Some leeches are long and worm-like, others pear-shaped and broad. Most can vary considerably in shape both between the elongated and contracted state and between the starved and replete condition.

Animals of general leech-like appearance -- with suckers, an annulated cuticle, and with looping motion -- are known also in the flatworms (Platyhelminthes). True leeches have a terminal or sub-terminal mouth, a straight gut (with or without diverticulae), posterior anus, typical annelid nervous system with ventral, single or paired nerve cords, and a closed circulatory system with distinct blood vessels. A majority of leech-like flatworms have the mouth non-terminal, the gut is blind, there are no internal coelomic spaces or internal segmentation and blood vessels are absent.

Five leech families are recorded from Australian inland waters:

1 Glossiphoniidae (Code LH019999)

Somewhat flattened body, the outline pear-shaped. Anterior sucker small and not well marked of from the body, posterior sucker discoid and placed ventrally.

2 Ozobranchidae (Code LH029999)

Body divided into anterior neck and posterior trunk. Branched lateral gills on the anterior trunk segments.

3 Richardsonianidae (Code LH039999)

Narrow, cylindrical body, not flattened or pear-shaped. Five pairs of eyespots. Dorsum with longitudinal stripes.

4 Ornithobdellidae (Code LH049999)

Narrow, cylindrical body, not flattened or pear-shaped. Five pairs of eyespots. Dorsum not striped.

5 Erpobdellidae (Code LH059999)

Narrow, cylindrical body, not flattened or pear-shaped. Three pairs of eyespots: one pair central anterior, two pairs several annuli further back and lower. Clitellum usually visible and covering about 15 annuli (= 3 internal segments)