Ellobiidae: Lost between land and sea

The Ellobiidae are a diverse group of archaeopulmonate snails living mostly near the sea, except for the Carychiinae which live in mountain forests and inside caves. The halophile ellobiids are commonly associated with the supratidal fringe of mangroves and salt marshes; they are, also, important components of the supratidal biota of the mobile rocky shore, namely under piles of rubble and shells. Their ecological requirements range from the muddy bottoms of stagnant mangrove embayments to the wave-swept crevices of exposed cobble shores, and they could be very important elements in the mineralization of the organic mud or algal detritus in such habitats. The various species of ellobiids occupy different portions of the shore, their distribution being loosely related to their taxonomic affiliation. The pythiinians (Pythia and, to a lesser extent, Myosotella) venture farther inland and may live in a nearly terrestrial environment, whereas the Pedipedinae prefer the upper intertidal. Within the Melampinae, some species of Melampus are found usually in mangroves and marshes, whereas others and Tralia prefer cobble shores. In rocky habitats, in addition to horizontal zonation, the ellobiids also partition their vertical distribution. The Ellobiidae range in size from barely 2 mm (Leuconopsis) to over 100 mm (Ellobium); the shell is variable in shape and can not be used as a reliable character for subfamilial allocation. The anatomy is also variable, but presents more reliable diagnostic characters. Six structural types of reproductive system set the boundaries for the subfamilial division, which is supported by the existence of three structural types of nervous system. The internal morphology of the penial complex has proven to be a helpful associated character in the subfamilial delimitation.