Code IF600000

Turbellarians are commonly called free-living flatworms. As the common name implies, most of its representatives are free-living, although some are know to be ecto- or ento-commensal or parasitic. The body is dorsoventrally flattened and is ciliated at least in part.

Turbellarians are mostly carnivorous and prey on invertebrates that are small enough to be captured or scavenge on the dead bodies of animals that sink to the bottom. The turbellarian gut is a blind sac, with the mouth functioning in both ingestion and egestion.

Most turbellarians are hermaphroditic, reproducing sexually by mutual copulation. In addition, several species reproduce asexually by transverse fission.

With in the Turbellaria there are four orders (Tricladia, Rhabdocoela, Alloeocoela and Temnocephala) that have freshwater representatives. Information on Temnocephala will not be found here as the order is covered elsewhere in this key. Distinguishing between the Tricladia, Rhabdocoela and Alloeocoela can be difficult as separation of these three groups is based on internal features. This is further complicated by the fact that special preservation and staining techniques are required to view these structures.

TRICLADIA - DUGESIIDAE

Code IF619999

Large, free-living flatworms. Very common in streams, lakes and ponds. This is the most well known of the freshwater flatworm families, and is widespread and common in Australia.

The body is elongate, strongly flattened, with the head region expanded laterally to give an eared effect and the neck region slightly constricted. Ventral ciliation is well developed but there are no cilia on the dorsal surface. Anterior ciliated pits absent. Two or more eye spots present. Posterior adhesive glands present. A muscular and glandular adhesive organ is present around the ventral margin.

The mouth is mid-ventral, the pharynx plicate (ie. muscular, and with a muscular protrusible tube from the inner surface) and directed backward. The gut is highly diverticulated and consists of 3-branches, one directed anteriorly and two directed posteriorly.

RHABDOCOELA

Code IR200000

A group of small flatworms, known from fresh, brackish and marine waters. Rhabdocoels are chiefly found on sandy and muddy bottoms, although they can also occur in flowing water and damp terrestrial habitats. The epithelium has numerous rhabdite and adhesive glands. In contrast to the Tricladia, the entire body is ciliated, although the number of dorsal cilia may be reduced or absent in some species. Most rhabdocoels have a pair of eyes. The mouth opens in the ventral anterior half of the body. The digestive system consists of a simple or bulbous pharynx and a blind saccoid to elongate gut. The contour of the gut is smooth, although sometimes slightly lobed.

Rhabdocoels generally reproduce sexually by mutual copulation. Asexual reproduction by transverse fusion is known within the group, particularly in the suborder Catenulida, which are commonly found as chains of zooids at various stages of development.

Some rhabdocoels can appear very similar to members of the Tricladia. The two orders can be separated based on the structure of the digestive system. Rhabdocoels lack the three branched, highly diverticulated gut characteristic of Tricladia. This separation can be difficult without the use of proper preservation and staining techniques.

ALLOEOCOELA

Code IF300000

A group of small to large (1-8 mm), slow moving flatworms known from freshwater, brackish, marine and terrestrial habitats. Specimens tend to be more cylindrical in shape when compared to Tricladia and Rhabdocoela, giving them a 'plump' appearance. The epithelium has numerous epidermal glands, and the body musculature is well developed. Eyes are usually absent.

The gut can be quite varied in structure, ranging from a simple sac to a highly diverticulated organ closely resembling the three branched gut of the Tricladia, except that the posterior portion of the gut is not fully separated into two distinct branches. Within the family Prorhynchidae the male reproductive system of some species incorporates a cuticularised stylet and muscular prostatoid gland which is used as a spear and poison gland for capturing prey.

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