Protobranchia is a subclass of bivalve molluscs. It contains the extant orders Nuculanida, Nuculida, and Solemyida.
These are deep water clams of a small and primitive order with a taxodont hinge (composed of many similar, small teeth), generally with a central ligament pit, large labial palps which are used in deposit feeding and the gills used only for respiration, the anterior and posterior adductor muscles are nearly equal in size, a foot which is divided sagittally and longitudinally with papillate margins. The foot in Protobranchia clams is without a true byssus gland, although they frequently have a nonhomologous byssal gland in the heel. The byssal gland in these clams does not produce threads as in Pteriomorphia.
2010 Taxonomy In 2010 a new proposed classification system for the Bivalvia was published by Bieler, Carter & Coan revising the classification of the Bivalvia, including the subclass Protobranchia.Bieler, R., Carter, J.G. & Coan, E.V. (2010) Classification of Bivalve families. Pp. 113-133, in: Bouchet, P. & Rocroi, J.P. (2010), Nomenclator of Bivalve Families. Malacologia 52(2): 1-184
Subclass: Protobranchia
Order: Nuculanida Source: Superfamily: Nuculanoidea Family: Bathyspinulidae Family: Lametilidae accepted as Phaseolidae Family: Malletiidae Family: Neilonellidae Family: Nuculanidae Family: Siliculidae Family: Tindariidae Family: Yoldiidae
Order: Nuculida Source: Superfamily: Nuculoidea Family: Nuculidae Family: Sareptidae
Order: Solemyida Source: Superfamily: Manzanelloidea Family: Manzanellidae Family: Nucinellidae Superfamily: Solemyoidea Family: Solemyidae
Order: † Praecardiida Family: † Butovicellidae Genus: † Butovicella Family: † Praecardiidae Genus: † Slava Genus: † Cardiola Family: † Antipleuridae Genus: † Dualina Genus: † Hercynella
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