A Method for Studying the External Anatomy of Copepods

TLDR

Clearing of fixed copepod specimens takes minutes to hours, varying with size and preservation duration. To prevent rupture, copepods are transferred through a mixture of their storage medium and lactic acid, layering the fluids to allow slow evaporation, and avoiding salt‑rich solutions by first moving specimens to alcohol or fresh water. Lactic acid proved the most effective clearing agent, and although copepods may initially contract in undiluted acid, they quickly return to normal size and shape.

Abstract

We have found lactic acid to be the best clearing agent for the preparation of temporary mounts of whole or dissected copepods. Fresh, alcoholic, or formalin fixed specimens become cleared within a few minutes to some hours, depending upon their size and the duration of preservation. When first placed in the un diluted acid, the copepods may become somewhat contracted, but soon regain, and thereafter retain, their normal size and shape. In order to avoid rupture, obese forms or specimens with a thin cuticle are best transferred through mixtures of the medium in which they have been kept and lactic acid. Since the latter is dense, layering the fluids in a small dish is usually satisfactory: the original medium will evaporate slowly, leaving the speci mens in the acid. Fluids with appreciable concentrations of dissolved salts, however, should be avoided, preferably by transferring the specimens first either to alcohol or to fresh-water.