- Phylum: Platyhelminthes
- Class: Turbellaria
- Order Polycladida
- Family: Leptoplanidae)
- Species: Notoplana australis
Most Turbellarians are less than 10 mm long which makes the Brown Flatworm seem rather large at up to 40mm. This species is distributed along the south-east Australian coastline including all of Tasmania and can also be found in New Zealand. Certainly here on the NW Coast it is fairly common on the underside of rocks at low tide.
It is carnivorous, feeding on bryozoans and other sessile invertebrates (attached to objects). It it sometimes seen as a problem for commercial shell fisheries as it has been found to eat oysters, hence it's other common name of Oyster Leach. However, it is believed that this flatworm only enters the shell when the oyster is already dying from some other cause.
The Brown Flatworm spawns all year with a peak in spring and early summer. The egg mass is a coiled, gelatinous string of individually encapsulated eggs. The eggs are only 120-125 µm (about 1/8th mm). The larvae hatch out after 12-14 days. It has planktonic larval stage with a gradual metamorphosis to a juvenile flatworm over a period of about 3 weeks.
- Diseases of cultured molluscs in Australia - Lester, R.J.G. 1990
- Australian Marine Life - The Plants and Animals of Temperate Waters - Edgar J. E. 2000
- The embyonic and laval development of the turbellarian Notoplana australis - Anderson DT 1977 - Australian Journal of Marine and Freshwater Research 28(3) 303 - 310