Within particular populations of Mauritia histrio from the East African coast, an occasional specimen with a black blotch on the base occurs. Recently, a population with shells predominatly blotched has been discovered in the south of Dar-es-Salaam, Tanzania. It is provisionally named
Mauritia histrio f. maculabasis nov.
In the widespread and highly diverse M. maculifera from the Pacific, a basal blotch is a characterizing feature. It is absent only in rare exceptions. To see this feature in occasional M. histrio from the Indian Ocean reveals that within the genetic variability of that species, a basal blotch may or may not be found. It also suggests that a common ancestor of M. maculifera and M. histrio was originally blotched, but the feature got reduced in M. histrio from the Indian Ocean whereas it is retained in M. maculifera in the Pacific. The shells of the population here called M. histrio f. maculabasis all show darker than usual pigmentation of the base, and all of them have some sort of black blotching. In some cases, it is quite extreme, more so than in M. maculifera. The marginal spotting is also remarkable, as it cosists of black spots on dark violet-grey background, as in M. maculifera and unlike other M. histrio from other places in Tanzania.
Fig. 1: Mauritia histrio f. maculabasis
Please note that the name maculabasis is not available as an official name in publications.