Dugesia

Dugesia species have an elongated body with a slightly triangle-shaped head. Usually they have grey, brown or black colors on the dorsal body surface, the ventral surface uses to be paler. These animals have a couple of eyes constituted by a multicellular pigmented cup with many retinal cells to detect the amount of light in the nearby environment. Sometimes they present supernumerary eyes. At the anterior part of the body, behind the eyes level, they have two of structures called auricles that give the triangle look to the 'head' and that allow them to detect the intensity of water current. These auricles are free of pigment and rhabdites. Each side of the anterior margin of the head have between 5 and 10 shallow sensory fossae, their number depends on the species or the individual. The sensory fossae and the auricle grooves are supplied with many nerve endings.[3]

Dugesia digestion tract consists of a central non-pigmented tubular pharynx. Like the other triclads, Dugesia's gut consists in three ramified branches. Each branch consists of ceca, which delivers the nutrients to the body. This worm has a sac digestive plan, that is, it does not have a separate opening for waste excretion.[4]

Subepidermal musculature is divided in four layers.[3]

In Dugesia the ovaries are ventrally situated, they start just behind the brain, usually at the level of the fourth intestinal branch. The bursal canal runs on the right side of the copulatory apparatus and above the atrium.[3] Like some Neppia species, Dugesia have a third layer of longitudinal musculature over the vaginal area of the bursal canal. This feature is not present in other triclads. Another feature shared with Neppia is the presence of a glandular area at the transicional area between the seminal vesicle and the ejaculatory duct, although in Dugesia these glands are concentrated at the diaphragm, a structure not present in any other genera.[5] Ball proposed that the presence of this glands was a synapomorphy of Dugesia and Neppia. The absence of these glands in some Neppia species (N. jeanneli, N. montana and N. schubarti) is thought to be a secondary loss.[6]

They are hermaphrodites. Many species can reproduce both sexually and asexually (by parthenogenesis or by fission).[7]

Dugesia species have not enough morphological characters to find out which are the relationships between them. Furthermore, those available use to contradict each other. Dugesia species are identified by the combination of diagnostic characters instead of different apomorphies. Over 70 species within the genus Dugesia have been described.[2]

Phylogeny

Dugesia cretica under a stone of a Cretan stream.

Dugesia sp. related to Dugesia liguriensis from Catalonia.

Phylogenetic tree including five dugesiid genera after Álvarez-Presas et al., 2008:[8]

Dugesiidae	Girardia       Neppia       Cura       Schmidtea     Dugesia

Molecular phylogeny of 13 Dugesia species after Lázaro et al., 2009:[9]

Dugesia	D. sicula      D. aethiopica              D. japonica        D. ryukyuensis        D. notogaea      D. bengalensis                D. subtentaculata        D. gonocephala        D. liguriensis        D. etrusca      D. ilvana              D. benazzii      D. hepta

Molecular phylogeny of Dugesia species after Solà et al., 2013:[10]

Dugesia	D. aethiopica     D. sicula             D. etrusca     D. ilvana         D. gonocephala       D. benazzii     D. hepta             D. cretica           D. elegans       D. damoae     D. effusa           D. improvisa     D. ariadnae           D. arcadia       D. malickyi       D. aenigma       D. sagitta     D. parasagitta

Wikispecies has information related to Dugesia.

• "Dugesia". Encyclopedia of Life. Retrieved 2011-04-23.
• Castilla, Juan C (December 2000). "Dos especies nuevas dedicadas al Dr. Patricio Sánchez R" [Two new species dedicated to Dr. Patricio Sánchez R]. Revista chilena de historia natural (in Spanish). 73 (4). doi:10.4067/S0716-078X2000000400009.