Dugesiidae
It is very likely that Dugesiidae is the best-known freshwater flatworm family among the non-specialist. Dugesiids are popular due to the recognizable triangle-shaped head that many of the family representatives present and due to their astounding regeneration capabilities. The family was erected in 1974 by Ian R. Ball and then included Dugesia, Cura, Bopsula, and possibly (sic) Rhodax. At the present, twelve genera are referred to Dugesiidae: Bopsula, Cura, Dugesia, Eviella, Girardia, Neppia, Recurva, Reynoldsonia, Romankenkius, Schmidtea, Spathula, and Weissius. The family has a wordwide distribution, excepting the Antarctica.
According to molecular phylogenetic results, Dugesiidae is the sister group of Geoplanidae or land planarians family. However, it is not clear whether Dugesiidae is a monophyletic family because some of its representatives (i.e. Spathula and Romankenkius) are phylogeneticaly closer to the land planarians than to the other Dugesiidae genera (Álvarez-Presas et al., 2008).
The type-genus of this family is Dugesia Girard, 1850.
This freshwater triclad family is characterized by the separate or combined opening of the oviducts into the bursal stalk or, less frequently into the atrium but very close and posterior to the entrance of the bursal stalk. Dugesiids are usually pigmented and present a couple eyes (sometimes also supernumerary ones) on the head. No adhesive organs are present and the presence of adenodactyls is rare. The inner pharyngeal muscles are split in two distinct layers. The bursal stalk usually receives the openings of the shell glands. The cocoons are spherical and with a stalk that attaches them to surfaces such as stones or submerged leafs.
Dugesiidae has a worldwide distribution.