AN ECHINODERM VITELLARIA WITH A BILATERAL LARVAL SKELETON: EVIDENCE FOR THE EVOLUTION OF OPHIUROID VITELLARIAE FROM OPHIOPLUTEI

¹ Smithsonian Oceanographic Sorting Center, Smithsonian Institution, Washington, D. C. 20560

Ophionereis annulata (Le Conte) possesses a barrel-shaped, yolky, non-feeding vitellaria larva with transverse ciliary bands. However, the larva develops vestiges of skeletal structures that are characteristically present in feeding ophiopluteus larvae but absent from vitellariae. Thus, it is evident that the vitellaria of O. annulata is a modified ophiopluteus. The presence of a pluteus-like skeleton in a vitellaria larva is suggestive that the evolution of ophiuroid larval types proceeds in a gradual fashion with a larval skeleton remaining after other ophiopluteus structures are lost. Ophiuroid vitellariae have apparently evolved from ophiopluteus larvae. These findings support Mortensen's (1921) proposal that the lecithotrophic vitellaria is a modified pluteus and contradict the hypothesis (Fell, 1945; Williams and Anderson, 1975) that vitellaria larvae are divergent and distinct from the feeding ophiopluteus larvae.