In his revision of the Paleartic unionids, Haas (1940) considered the three Moroccan species described by Pallary (1918, 1923 and 1928) to belong to a single subspecies of the European Psilunio auricularius (Spengler, 1792 ), namely P. auricularius marocanus. Some authors (Van Damme 1984; Ghamizi 1998) retained the Moroccan form as distinctive while others (Mandahl-Barth 1988; Daget, 1998) did not. Recent molecular and conchiological investigation show that this species is a separate species, differing from the European species e.g., by its smaller size, nearly black outer test and differences in the hinge.

This species is restricted to one location in the Oued Derna (a very small population with a range of about 100 m, sampled in 2006) and two locations in the Oued Beth (population size assumed small, range 300 m, sampled in 1990s). There has been a massive population reduction (greater than 80%) in the last 100 years (and species generation time 50-100 years), meaning it qualifies as Critically Endangered.

The estimated remaining population size is fewer than 250 individuals with an estimated continuing decline of more than 25% in 1 generation. The decrease in the past has been alarming. The species depends for its propagation on a host fish species presently unknown. Most likely this is a salmonid or a blenny. The dramatic reduction of the European Pseudunio auricularius has been mainly due to the disappearance of the migratory host fish. Damming and impounding of rivers is probably also the cause for the rarefaction of this species also.

This species used to be found in the permanent rivers of Atlantic northwest Morocco, from the Oued Sebou till the Oued Oum er Rbia. The type locality for this species is Oued Fès, a tributary of the Oued Sebou (where it is now extinct). It occurred all along the river in large quantities according to Pallary, but is now located in a few tributaries in the upper mountains, including Oued Denna and Oued Abid (both in the Oum Rbia basin), and Oued Beth, in the Sebou basin.

There has been a massive reduction in the last 100 years and the estimated remaining population size is fewer than 250 individuals with an estimated continuing decline of more than 25% in 1 generation.

This species is a large (up to 17 cm), long lived (80 -100 years) najad. It occurred in the lower and middle parts of the Oued Sebou and Oued Oum er Rbia hydrographic systems but is presently restricted to two tributaries of the latter where it is found in deeper parts of the river (ca. 2 - 8 m) on coarser sediments. As virtually all unionoids is the larva ectoparasitic on a fish host, that as yet is unknown. It relies on a host fish so makes it particularly vulnerable. Host fish is probably trout which is also Endangered because of pollution.

This species was possibly collected (until the 19th century) for pearls since the old name of the Oued Derna is River of Pearls. The major threats for the few surviving populations are pollution or any kind of mechanical alteration/disturbance (impoundment, canalisation, dredging, etc.) to the waterbodies in which they still persist. Further rarefaction of their fish host or hosts or any type of activity causing barrier-effects for the fish hosts also constitute a major threat, as it relies on a host fish, probably trout, which is also threatened because of pollution.

This species was possibly collected (till the 19th Century) for pearls since the old name of the Oued Derna is River of Pearls.

This species is in need of conservation measures. In Spain, in situ (stringent protective regulation) and ex situ (successful breeding and reintroduction projects) have been instigated since ca. 1995 for the protection of Pseudunio auricularius. For breeding experiments, the easily reared Siberian sturgeon, Acipenser baeri, was successfully used as a substitute for the European sturgeon, Acipenser sturio (see Araujo and Ramos 2000, 2001, Machordom et al. 2003)). In France a similar project for Pseudunio auricularius has started in 2007 (see also Cochet, 1999, 2001, 2002).

In Morocco no protective measures have as yet been taken even though this species is even more threatened than its European relative . Ecological research on the Moroccan species and the instauration of conservation measures should be given priority since it is so rare and the few representatives of the Margaritiferidae in the world are all rare and most are protected.