Shell flat, inequivalve, inequilateral, extremely variable in shape; the hinge is devoid of teeth, but bears some marked transverse pits in which the ligament, external, is anchored. There is a byssal gape below the anterior auricle. The family, introduced by W. P. Woodring in his Miocene Molluscs from Bowden, Jamaica, Washington 1925, contains nowadays only the genus Isognomon.
Isognomon Lightfoot, 1786:
Many synonyms, among which Malleoperna, Parviperna, Pedalion, Perna, Pernaria… suggest some characteristics. The genus lives attached to various substrata: rocks, wrecks, sponges (endozoism), roots, rhizomes of Posidonia oceanica in Mediterranean, gorgonians(epizoism)…
