Algae World: Phycological Research

Image: type specimen of Sellaphora lanceolata.

Types are used to determine how the names of diatom species are to be used, just as in other groups of organisms. Types are sometimes individual specimens, mounted in resin on a microscope slide, but more often they are whole slides, prepared from a mixed natural population containing several or many specimens of the species that the slide typifies, together with specimens of many other species. The use of whole slides as types is allowed by the International Code of Botanical Nomenclature, but it would be much better to designate a single specimen, to provide an unambiguous reference point for comparisons. Some diatoms are typified by images.

Nowadays, when a species is described for the first time, the author(s) of the description must specify a type specimen and this is called the holotype. In the past, this was not mandatory and so for species originally described without a type, taxonomists have to choose a specimen (or slide) on behalf of the original author. This may be a lectotype, if appropriate specimens studied by the original author still survive, or a neotype, if they do not. In addition, if the holotype, lectotype or neotype do not exhibit enough characterictics to define the species adequately and unambiguously, an epitype can be added. These procedures aim to stabilize and clarify the use of the names that all other biologists use for communication: though they appear arcane, they are important.

In AlgaeWorld, you can find information and images for some type specimens. We have produced stacks of images, by focusing through specimens manually or with a computerized microscope, and we present these stacks here so that you can look at type specimens almost as though you were looking down a microscope. By sliding a focus button or running a short video sequence, you can focus up and down through the specimens to see  details that may be of importance for identification and comparison – in this way, we can give you much more than can be seen in a single photograph.