Structure and properties of hyaline spheres in holothuroid larvae

Abstract

Summary The structure of the hyaline spheres (HS) in the larvae of the holothuroids Parastichopus californicus and Stichopus japonicus was examined by electron microscopy, and their sensitivity to a range of hydrolytic enzymes was tested. The HS are attached to epithelium and extend into the blastocoel. They consist primary of extracellular material but scattered cells surround them, and a few are found within matrix. Ultrastructurally, the matrix has a gel-like appearance and contains fine granules and fibrils. HS are dissolved very specifically by hyaluronidase (10 mg/ml, pH 5.4). Pronase, trypsin and papain at the same concentration damage both HS and the larval body to varying degrees. Surprisingly, HS sink when isolated from the larval body, so it is unlikely they serve as flotation devices. It seems more likely they serve as storage of structural elements utilized after metamorphosis.