Schmidtea mediterranea Benazzi et al., 1975 is a freshwater planarian (order Tricladida, suborder Continenticola, phylum Platyhelminthes) that is mostly known to the scientific community for its capacity to regenerate and has become a model organism for the functional analysis of the genes involved in pattern formation.
Schmidtea mediterranea populations are scattered and in some of the localities a population decline has been observed. This is the case of the asexual populations of Montjuïc (Barcelona) where it has apparently disappeared from two ponds after human intervention. In another pond of Montjuïc (Viver dels Tres Pins) the introduction of Schmidtea polychroa in 2007 seems to have had a deleterous effect on S. mediterranea population. The fourth pond with this species, “Pantà de la Fuxarda”, has been invaded by the crayfish Procambarus clarkii (Girard, 1852). Its introduction could menace S. mediterranea because its known to be able to change native plants and animal communities.
It has been suggested that the common ancestor of S. mediterranea and its sister species, S. polychroa, diverged around 43 mya. S. mediterranea appeared at some time between these 43 mya and 20-5 mya.
It is present in coastal locations and islands in the western Mediterranean: Catalonia, Menorca, Mallorca, Corsica, Sardinia, Sicily and Tunisia. Their populations are scattered.
In Catalonia, and in the whole Spain, only two populations are known. One is located in the Montjuïc Mountain, within Barcelona city. Specimens from Girona are also known, but recent searches didn't succeed in finding them.
Despite its present distribution in the Mediterranean, S. mediterranea seems to be adapted to moderate summer temperatures. That leads to think that this species is probably trapped in the Mediterranean since this area had a more suitable climate.
There are either amphimictic and/or asexual fissiparous populations. In both types of reproduction most of the populations are diploids.
The individuals that reproduce by fission (either diploids and triploids) bear a heteromorphic translocation between first and third chromosomes. This translocation only affects one chromosome of each pair.
The asexual populations are only present in Catalonia, Mallorca and Menorca. There is no sexual population known in this locations. The Menorca asexual population is triploid, while Catalonia and Mallorca populations are exclusively diploids.
Most of sexual populations are diploids with an exception, one in Sardinia is triploid.
Schmidtea mediterranea is used in developmental and regeneration studies.
