The Larval Development of Ophelia Bicornis Savigny

Abstract

Fertilizations of Ophelia bicornis Savigny were made and the larvae reared. This is the first time the larval development of any member of the family Opheliidae has been described.The trochosphere is small and somewhat yolky; it has a broad prototroch, a narrow telotroch, a strong apical tuft and a long anal cilium.Annulation is accompanied by the appearance of parapodial lobes and bristles. When the first pair of bristles of the third setiger protrude the larva is ready to metamorphose. It has two, sometimes three eyes.The larva in its later stages can adhere strongly to solid objects, such as sand grains, by a secretion from the four anal papillae and the parapodial lobes. This is interpreted as an adaptive aid to settlement on sand banks swept by strong currents.At metamorphosis the larval external cilia are lost and the bristles rapidly elongate, especially those of the third setiger.Some of the larval bristles are slightly winged. So far only capillary bristles have been known in the Opheliidae.It is pointed out that a development such as that of Ophelia is more typical of polychaetes as a whole than are the developments of certain species commonly used as text-book types.