Ciliary feeding of tornaria larvae of Ptychodera flava (Hemichordata: Enteropneusta)

Abstract

Ciliary feeding by tornariae of Ptychodera flava (Eschholtz) and other tornariae from the plankton is compared with Garstang's (1939) account of feeding by these larvae, which account contains errors, and with ciliary feeding by echinoderm larvae. Some details of ciliation are also described. As in echinoderm larvae, band cilia beat away from the food grooves and retain particles on the upstream side of the ciliated band, but tornariae use muscles less in ingestion and rejection. In early-stage and most late-stage echinoderm larvae, the ciliated band functions in both swimming and feeding, but in tornariae the ciliated band is arranged meridionally so that few portions of the ciliated band produce a posteriorly-directed current and a locomotory teletroch is needed for swimming. Faster-swimming tornariae observed in bowls achieved higher ingestion and clearance rates. These observations raise questions about form and function in the giant Planctosphaera pelagica. Cilia of the locomotory telotroch increase in length as tornariae increase in size, but there is little increase in length of cilia which capture food. Instead, the length of the ciliated band increases relative to other larval tissues by means of increasing convolution of the band. Hence, the volume of water processed for food probably increases relative to energy expended by larvae during development to the tentaculate stage. However, the length of the ciliated band may decrease relative to other larval surfaces with continued increase in size beyond this stage. These interpretations of growth and feeding efficiency are consistent with the reported geographic distribution of tornariae with and without tentacles.