Mauritania has a few mythic languages, including Imraguen, used by a coastal fishing group which used dolphins to fish. This you tube video claims to tell the story of how they fish: "With ancient rituals, they call to the dolphins by simulating the sound of leaping fish slapping the water. Finally the dolphins come, driving the mullet before them. Perhaps the dolphins are using the fishermen to gather a feast for themselves, in a spectacular display of interspecies cooperation."
Unfortunately, the Imraguen people only speak normal Hassaniya, though with a purported Azer influence, which has not been confirmed.
Another phantom language, Nemadi, also has a supposed Azer influence - which is actually a bit more likely, since they live in the Western Hodh region which also has a fair number of Soninke speakers, and is adjacent to Mali. More recent work has shown that the Nemadi is probably just Hassaniya with a few technical terms dealing with the hunting which those people do, with dogs no less, to complete the "spectacular display of interspecies cooperation." In Hassaniya they are called Ikokol.
In that same region are some other minority languages -a number of others have commented on Hassaniya language contact in use on the Mauritania-Mali border, I came across some non-linguistic academic work that suggests there is another language that is somehow distinct there. The surprisingly large amount of trade that occurs in the Modibougou market area has obviously led to a need for a trade language, or perhaps a language used by unassimilated Haratine, as this comment on the relationship between Beydhan and the economy of the Southern Hodh suggests:
"An example of the relationship between society and nature may be found in the villages of the southern part of the Hodh, and with which this study is concerned. In the area of rain-fed agriculture along the Mauritanian border with Mali are found numerous Haratine villages, known as adweba (singular debaye). Debaye is an offensive term to urban and politicised black Moors but is apparently perfectly acceptable in rural and remote eastern Mauritania. It is possible that the word derives from the word debba, for a beast of burden. If this is the case the word may be a semantic remnant of slavery itself, and point to a former function of Haratine villages in the southern Hodh. Thus, it is possible that many of the villages in the south of the Hodh were founded as summer grain-growing camps, visited by kabila overlords (Bidan Moors) only at harvest time. Regardless of the actual present legal status of the villagers, the practice of harvest-time visits to Haratine villages by Bidan Moors to receive free handouts of grain continues to this day, as the thesis will show. There are only very few signs that the practice is beginning to be questioned. This intriguing possible reason for the settlement of some villages may be supported by the actual names of some of them. For instance, two of the very largest Haratine villages of the central southern border area of the Hodh el Gharbi, Kerkerette Mohammed Saghir and Kerkerette Amar Beyou, belong to the Mohammed Saghir and Amar Beyou fractions of the Oulad an Nasser kabila respectively. Kerkeru in Bambara means ‘granary’, and kerkerette is the Arabised plural of kerkeru. It is therefore possible that these two large villages were founded as a source of grain for people living far beyond the actual village boundaries."
In addition, though, there seems to be a creole that has developed which is actually the 'mother tongue' of some villages like this one, called J'reif:
The village of Jreif is situated about 9 kilometres north of the border with Mali and about 4 kilometres south-west of the main village of Modibougou. As with Mosfeya, the village is due south of Aioun el Atrouss.
The exact ethnicity of the villagers of Jreif is unclear. The villagers are known locally as اهل الترني, meaning, ‘family of Terenni’. They say that they are of ‘Macina’ origin—presumably after the Macina empire of northern Mali of the 17th and 18th centuries. The story they relate about their origin is that under the leadership of their mysterious first ancestor, Mohammed el Hanchi—a being alleged to have been half-man, half-serpent—they migrated south from Tichit in east central Mauritania to the Aioun area, at the time when the ‘rocks were still wet’ (meaning when the rock escarpments around Aioun had not yet been fully formed, or when ‘the rocks were still soft’). This narrative appears to contain both fact and legend. Then, from a settlement close to the site of modern Aioun, they migrated south to Mali but came north again to their present location in 1905 in order for the men to avoid being drafted into the colonial army by the Malian authorities. The villagers also refer to themselves as Bidan or ‘white’. Almost all villagers have some knowledge of Hassaniyya Arabic, yet among themselves they appear to speak neither Arabic nor Sonninké—their own language appears to be a mixture of the two, possibly with a Berber element. The village seems to be integrated to some extent with the local Moorish kabila structure: they are allied with the Oulad an Nasser clan, yet do not appear to have been slaves at any time in the past, unlike most of the other Haratine villages of the area. Their exact origin remains a mystery, although this is not from want of asking questions.
Thanks goes to Jason Lawton for sharing this field work...