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Order Acoela Uljanin, 1870


Small turbellaria without a gut lumen, mouth entering directly (or via a pharynx simplex) to the parenchyma. A statocyst with a single statolith almost invariably present. Without protonephridia. Hermaphroditic, gonads or germinal tissue lie free in the parenchyma, eggs entolecithal, sperm biflagellate, penis usually unarmed. Predominantly free-living and marine.


Anaperidae Dörjes, 1968
Antigonariidae Dörjes, 1968
Antroposthiidae Faubel, 1976
Childiidae Dörjes, 1968
Convolutidae Graff, 1904
Diopisthoporidae Westblad, 1940
Hallangiidae Westblad, 1949
Haploposthiidae Westblad, 1949
Hofsteniidae Bock, 1923
Mecynostomidae Dörjes, 1968
Nadinidae Dörjes, 1968
Otocelididae Westblad, 1949
Paratomellidae Dörjes, 1966
Proporidae Sabussow, 1900
Solenofilomorphidae Dörjes, 1968


Comprehensive accounts of these worms are given by Westblad (1940-49) and more recently by Dörjes (1968). The classification of the latter is adopted here. Bush (1981) has also given an illustrated key in English similarly based upon Dörjes. By and large these animals are difficult to identify. Reference should be made to the authors of the genera (or Dörjes, 1968).
Two additional families have been recognised. Taurididae Kostenko, 1989 was erected to contain Taurida fulvomaculata (Ax, 1959) and Sagittiferidae Kostenko and Mamkaev, 1990 was split from the Convolutidae: it has two subfamilies Praesagittiferinae containing Praesagittifera Kostenko and Mamkaev, 1990 and the Sagittiferinae with two genera Sagittifera Kostenko and Mamkaev, 1990 and Simsagittifera Kostenko and Mamkaev, 1990.

Order Acoela