Etheriidae

Abstract: Abstract A robust phylogeny for the Unionoida is emerging and presumed relationships of some major clades are being questioned. The Etheriidae or freshwater oysters has been a distinct family for over 160 years and currently contains three cemented genera: Acostaea (Columbia, South America), Pseudomulleria (India) and Etheria (Africa and Madagascar). Starobogatov (1970, Nauka, 1–372), Mansur and da Silva (1990, Amazoniana, 11(2), 147–166) and Bonetto (1997, Biociências, 5, 113–142) present conflicting testable hypotheses regarding the evolution of these taxa. Using cytochrome c oxidase subunit I DNA sequences the evolutionary relationships of these three genera has been examined, by comparing them to representatives of 30 other unionoid taxa from around the world. These analyses place Acostaea and Etheria within the Mycetopodidae while Pseudomulleria falls within the Unionidae. A monophyletic Etheriidae, composed of cemented freshwater bivalves, is not supported by the present analyses. Furthermore, the analyses indicate that cementation in the Unionida has evolved at least twice.

Abstract: The objective of this study was to assess freshwater mussel (Mollusca: Bivalvia: Unionoida) species distributions among the freshwater ecoregions of Africa and Madagascar to discover areas of high richness and endemism. These are among the top criteria for identifying biodiversity hotspots and establishing conservation priorities. Distributions were determined from museum specimens in 17 collections. In total, 5,612 records for 87 unionoid species could each be assigned to one of 90 freshwater ecoregions. The majority of species (55%) are known from only one (34 spp.) or two (14) ecoregions. Only three are known from more than 20 ecoregions: Etheria elliptica (38 ecoregions), Chambardia wahlbergi (25), and Mutela rostrata (21). The most species-rich ecoregions are Lake Victoria Basin (17 spp.), Upper Nile (16), Upper Congo (14), Senegal–Gambia (13), and Sudanic Congo–Oubangi (13). Those with the most endemic species are Lake Tanganyika (8 spp.), Lake Victoria Basin (6), Bangweulu–Mweru (4), and Lake Malawi (3). Twenty-five ecoregions have no known freshwater mussels. These patterns are significantly correlated with fish and general freshwater mollusk richness. Unionoid richness also varies significantly among major habitat types. These patterns are relevant to biogeography and conservation and indicate areas in need of further research. We argue that freshwater mussels are valuable as focal species for conservation assessments, and they themselves merit management consideration for their ecosystem functions and distributions in imperiled habitats. It is recommended that field surveys be conducted to determine the current status of species in all areas of Africa and Madagascar.

Abstract: The palaeobiology of the Late Cenozoic freshwater molluscs that inhabited the Omo-Turkana Basin, situated in the eastern branch of the East African Rift System (Ethiopia, Kenya), remains poorly documented. Here we revise the taxonomy and palaeobiology of the bivalve superfamily Etherioidea from this region and discuss some palaeohydrological implications. In the Iridininae (Mutela, Pleiodon), the genus Iridina Lamarck, 1819 is revived for elongated iridinids with a denticulated hinge, since all fossil Iridininae of the Omo-Turkana Basin and most Miocene-Early Pleistocene Iridininae elsewhere in Africa have denticulate hinges that are not comparable to those of modern Mutela. In addition to the ubiquitous Etheria elliptica (Etheriidae), 11 iridinids are described, five of which are new to science, namely Chambardia feibeli, Iridina turkanica, I. omoensis, I. browni and Pleiodon bentoni. Most species do not show lacustrine adaptations and are/were part of a widespread East African fauna. This confirms the highly unstable character of the Pliocene-Holocene aquatic ecosystems in the Omo-Turkana Basin. Indications for intralacustrine speciation are only observed in the Late Pliocene-Early Pleistocene long-lived (similar to 250 ka or longer) Palaeolake Lorenyang. Williamson's (1981) evolutionary model for the Omo-Turkana Basin molluscs does not apply to the Etherioidea.

Abstract: Recent molecular approaches to taxonomy have led to a steady increase in the identification of cryptic species. Within the Etheriidae, the species Etheria elliptica (freshwater oyster) is widespread and common and exists in most of the major African drainages. Within the African freshwater ecosystems, there are major threats to biodiversity and cryptic species complicate conservation strategies; unknown species exist and no conservation status has been assigned. Our objective here was to determine if E. elliptica from several locations in the Congo drainage are correctly classified as representing a single species. We analysed the genetic diversity at two mitochondrial loci (COI and 16S) and two nuclear loci (H3 and 28S), and estimated evolutionary relationships using phylogenetic and DNA barcoding techniques. Bayesian inference yielded three cryptic species of Etheria, and mismatch analysis revealed discrete differences between the cryptic species. We identified three cryptic species within these collections, and evidence indicates that the third species may resolve further with more sampling. In conclusion, the taxonomic history of E. elliptica makes finding cryptic species unsurprising. However, molecular studies such as this may finally help to resolve the number of species within this genus.