The identity of Yoldia micrometrica Seguenza, 1877 and three new deep-sea protobranchs from the Mediterranean (Bivalvia)

Three new species are described from the relatively well-known deep Mediterranean protobranch fauna. Yoldiella wareni n. sp. is a miniaturized species so far misidentified as Yoldiella micrometrica (Seguenza, 1877), which is a Pleistocene species (neotype here designated). Yoldiella ovulum n. sp. is similar to Y. micrometrica, of which it may represent a descendant species. Ledella marisnostri n. sp. is the second species known for the genus in the Mediterranean. These three species are thought to be endemic to the Mediterranean, where they may represent either persisting Plio-Pleistocene species which survived the changes from psychrospheric to homeothermic conditions, or newly adapted species, evolved from Plio-Pleistocene ancestors. In the second case, they seem to be the result of an ongoing differentiation of the deep Mediterranean protobranch fauna from the North-East Atlantic one, due to the physical isolation of the Mediterranean basin.