Propeamussium (Parvamussium) mistensis, Hickman, 2023

Hickman, Carole S., 2023, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs, PaleoBios 40 (5), pp. 1-51 : 36-37

LIMIDAE RAFINESQUE, 1815

Placed within their own order and superfamily (Waller 1978), the limid bivalves, commonly known as file shells, have a long geologic history. They appeared in the Carboniferous but failed to diversify to the extent of most pteriomorph groups. The living species are predominantly small-shelled, tropical, epifaunal forms that nestle, attach, or construct byssal nests. Many species are conspicuous in their brightly pigmented hypertrophied mantle tissue and long pallial tentacles, and their ability to swim when disturbed. Internal relationships within the family remain unresolved, despite the remarkable detail with which many living species have been studied. Mikkelsen and Bieler (2003, 2008) and Harasewych and Temkin (2015) provide new data and review previous studies, raising the challenge of a comprehensive worldwide phylogenetic study based on morphological and molecular data. From a deep- time perspective this program must include the fossil record!

Of special interest here are the fossil giant limids (height frequently> 200 mm) assigned in this study to five genera. The two species treated below are assigned to Acesta H. and A. Adams (1853) and Plicacesta Vokes (1963) . There are three additional available names for the large-shelled obliquely ovate species—the extinct Cretaceous Costellacesta Kauffman (1964) , the extinct Eocene Antarcticesta Stilwell and Gaździcki (1998) , and Oligocene–Holocene Callolima Bartsch (1978) .

Although members of the family are easily recognized, the genus-group placement of the deep-water species has become increasingly difficult as ROV dives provide in situ video data on ecology and behavior and recover live specimes with new combinations of shell and anatomical features. Extremely thin translucent shells of Acesta vitrina Poppe, Tagaro and Stahlschmidt (2015) are uncomfortable in Acesta , resulting in description of the new monotypic genus Acestarica Dekkers (2022) . However, significance of the translucent shell is questionable—anatomical and molecular data from the small deep reef Mantellina translucens Haraewych and Tëmkin (2015) place Mantellina outside a main limid clade in which Acesta and Lima are sister taxa. Because the type species of Mantellina Sacco (1904) is a Miocene fossil, phylogenetic resolution of the bathyal limids is especially challenging.

Stratigraphic Range —Lower Carboniferous–Holocene.