Order CATENULIDA Meixner, 1924
Introduction
According to Ax (1984), these are perhaps the simplest of the flatworms. These worms are predominantly freshwater and, apart from Schmarda (1859), have not been recognised formerly in Australia. Williams (1980) reports undescribed specimens from Australian environments.
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Diagnosis
Delicate worms with poorly differentiated parenchyma, pharynx and gut simple. Vegetative reproduction via paratomy common. Usually lacking statocyst. Unpaired protonephridial system arising caudally and running dorsally forward and then ventrally backwards to discharge posteriorly (2 groups described from marine environments lack protonephridia). Oocytes entolecithal; testes dorsal with penis antero-dorsal, male organs often lacking. Free-living, freshwater (although some marine groups have been described).