A New Device for Sorting and Counting Small Crustaceans

Abstract

Counting and sorting organisms in samples obtained from field work is often a task which requires much effort, e.g., working with small crustaceans (Am phipoda, Copepoda, Isopoda, Entomostraca) which must be examined using a stereoscopic microscope. The several methods at present available do not resolve satisfactorily the problem. A review of such methods is found in Lienz (1972). Newell (1977) pointed out Whatever method of subsampling and ex amination is adopted, the counting of individual organisms is bound to be a tedious business. Trying to make easier the counting and sorting task, we have designed a simple device and developed the technique to use it as ex plained below. The device is a Petri dish into which is placed a spiral made from glass rectangles joined with glue (Silicon works well), thus forming a con tinuous canal within the Petri dish (fig. 1). To facilitate the handling of forceps and droppers, the spiral has a lesser height than the dish wall. Plastic separators (a, b in fig. 1) are suspended vertically across the canal.