Ростроконхии: вымерший класс моллюсков

Extinct class of molluscs
Automatic taxobox
| name = Rostroconchia
| image = Technophorus sharpei. svg
| image caption = Technophorus sharpei
| fossil range = fossil range|525|Permian|Cambrian Permian|ref= Adult rostroconchs differ from bivalves because they have no functional hinge. Unlike the shell of a bivalve, which was able to move or articulate, the shell layers of a rostroconch — the layers of rigid calcite— continue across the whole dorsal area of the rostroconch. The two valves would have been rigidly fixed in place, and would have to have been broken periodically to allow the rostroconch shell to grow. The posterior of the shell contains a flattened tube that is called the rostrum. The rostroconch probably burrowed itself into sediment, anterior first, leaving the rostrum above the sediment to be used as a water filtration system.

Heraultipegma is the earliest, very primitive, rostroconch genus dating from the Late Terreneuvian. True Rostroconchs appeared during the Ordovician, heavily competing with the bivalves until their decline in the end early Ordovician turnover. Early, primitive rostroconchs such as Ribeiroia had a hinge in which all shell layers covered the dorsal region resulting in a very rigid shell. In Conocardium, a more advanced rostroconch, the outer shell layers do not cross the entire margin, suggesting independent steps towards the bivalve flexible hinge. Some evidence suggests that the conocardoid rostroconchs were the predecessors to the Scaphopoda.