Animal medium-sized, topped by a limpet-shaped shell that protects the visceral mass. The differences with Umbraculidae are anatomical: the animal is elongated and smooth in Tylodinidae, globular and pustulose in Umbraculidae.
Tylodina Rafinesque, 1814:
« Body narrow bearing, above the back, a small external shell, membranous, oval, without spire, with a calloused tip… » – C. S. Rafinesque: “Definizioni di 36 nuovi generi di animali marini della Sicilia”, Specchio delle Scienze o Giornale Enciclopedico di Sicilia vol.II, Palermo 1814, p.162.
