Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Platyhelminthes
Class Turbellaria

Common names: flat worms, turbellarians

Overview

Turbellarians are bilaterally symmetrical and largely free-living, however the group does include some symbiotic and parasitic species. Most species are small (1-2mm long) but some terrestrial triclads and marine polyclads can grow much larger. The classification �turbellaria� has been shown to be paraphyletic, but is still used as a convenient way to group together those orders which are not exclusively parasitic.

Distribution and diversity

There are over 4500 species of Turbellaria described worldwide, however many of these belong to entirely marine groups such as the Polycladida. Freshwater turbellarians in Australia are poorly studied, but there are known species in several orders. The classification system within the class is regularly changing as new molecular studies are carried out. The following groups are known from Australian freshwater or terrestrial environments.

Seriata: Contains the Tricladida, one of the most commonly encountered and most studied groups of turbellarians.
�Dalyellioida�: A group including the Temnocephalida, which are easily identified by the presence of 2-6 anterior tentacles. Species in this group are found in freshwater environments all over Australia.
Typhloplanoida: There are several genera known from Australian freshwater environments, including Phaenocora, Gyratrix, Haplodidymoa and Mesostoma.
Macrostomida: The first record of this order in Australia is Promacrostomum palum from freshwater springs in New South Wales.
Acoela: One species from this order, Childianea coomerensis, is described from salt marshes in Queensland.
Lecithoepitheliata: Prorhynchus tasmanensis is described from a freshwater lake in Tasmania. Two other species are known from New Zealand.
Prolecithophora: A species in the genus Icthyophaga is described from Lizard Island, off the coast of Queensland.
Catenulida: This group is sometimes placed outside the Turbellaria. There are no described freshwater species from Australia, but undescribed species are known to occur.

A key to these groups can be found at �Turbellaria of the World: A Guide to Families and Genera� by L.R.G. Cannon

Life cycle

Turbellarians are generally simultaneous hermaphrodites, requiring copulation with another individual for fertilisation. Most lay egg capsules from which young emerge and develop into mature adults. However, some groups, such as the Catenulida, can produce by asexual reproduction.

Feeding

Most species are carnivorous, eating small crustaceans and other small aquatic invertebrates. Some species are primarily scavengers, feeding off of detritus and dead fish and molluscs. Turbellarians typically have a mouth and muscular pharynx for catching food and a sac-like gut, and as they have no anus, wastes are regurgitated.

Ecology

All turbellarians live in aquatic environments or moist terrestrial environments such as damp soils. Some species are used as environmental indicators because of the speed at which they can respond to changes in water quality.

Catenulida: Catenula lemnae from Europe
Image credit: Christopher Laumer
used under a Creative Commons Attribution license

Seriata: Caenoplana coerulea
Image credit: Duncan Farquhar
used under a Creative Commons Attribution license

Seriata: Caenoplana coerulea
Image credit: John Tann
used under a Creative Commons Attribution license

Seriata: canary worm, Geoplanaria sugdoni
Image credit: Kristi Ellingsen
used under a Creative Commons Attribution-NonCommercial license

Seriata: Cura pinguis with egg cocoons
Image credit: � Lauryne Grant
used with permission

Seriata: Anisorhynchodemus cf guttatus,
"the spotted flatworm", with egg cocoon
Image credit: � Ken Walker, used with permission

Seriata
Image credit: Photographer: Erich S. Volschenk
� Western Australian Museum

Temnocephalida (not an Australian species) on crayfish host
Image credit: Alan Couch
used under a Creative Commons Attribution license

Temnocephalida
Image credit: Photographer: Erich S. Volschenk
� Western Australian Museum

Macrostomida: Macrostomum sp. (not Australian)
Image credit: Wim Willems
used under a Creative Commons Attribution-NonCommercial license

Typhloplanioda: Gyratrix hermaphroditus
Image credit: Christopher Laumer
used under a Creative Commons Attribution license

References and further information

ABRS Australian Faunal Directory: Turbellaria
Atlas of Living Australia: Turbellaria
Encyclopedia of Life: Turbellaria
Tree of Life: Platyhelminthes
Identification and Ecology of Australian Freshwater Invertebrates

This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Australia License.