Flatworms
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A colourful flatworm on the Great Barrier Reef |
Most flatworms belong to the complex community of animals live in marine sands. Four groups of flatworms are found within the Great Barrier Reef Marine Park. These include:
- macrofaunal (large free-living worms)
- meio-faunal (small free-living worms)
- interstitial (less than 1 mm); and
- symbiotic (these worms live in a mutually beneficial arrangement with other species)
Marine flatworms include members of the Phylum Platyhelminthes and the Class Turbellaria. Most of the tube worms are tiny, from less than one millimetre to several millimetres long, longer than they are wide, and more or less cylindrical. Some of the larger members of the group may be several centimetres (occasionally over a metre) in length, with flattened bodies, hence the name flatworm.
Habitat
Known as interstitial fauna or meiofauna, these animals live in the water-filled spaces between grains of sand. Many occur in great numbers. The spaces between the grains of sand create a complex three-dimentional labyrinth through which the animals move, feed and reproduce. But the spaces are small and the sand shifts as water flows over and through it. The animals that inhabit this lively Lilliputian world tend to be very small, but elongated.
Locomotion
The different species of Turbellarians move in lots of different ways. Some have cilia along their bodies
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Flatworms occur in a wide range of shapes and patterns |
Feeding
Turbellarians are mainly carnivorous, feeding on other invertebrates small enought to be captured, and on the dead bodies of animals that sink to the seabed.
Threats
Because most of these animals are in the size range of plankton, they risk being washed out of the sand and into the water, especially in areas scoured by currents and tides. As a result, most interstitial animals have adhesive organs that enable them to grip grains of sand.
