How do you identify them?
What is a species?
This can be difficult to assess. Perhaps the best definition is that if two indivuduals can interbreed and produce viable offspring they belong to the same species. However, this definition does have problems not least how do you test it? Maybe the most usable definition is ”a species is whatever a competent taxonomist says it is”. This is also not without major problems but at least we have a starting point.
So, how do we determine what species of invertebrate we have? Often this is a difficult task requiring a specialist in the particular group of animals. Traditionally, species are separated by morphological differences, that is differences in the shape and form of the body. For example, two species may be separated by the position of body hairs (setae), pores on the body or number and position of any eyes. Drawings are made to show these features (see figure at the top of the page). The charateristic features are named to enable comparison between individuals and species. In the example here the rows of hairs (setae) used to distinguish between two species are JV or ZV with each particular setae numbered. Fig. 1 shows how these features may appear once the animal is viewed through a microscope.
To enable a species to be determined, specialists have written ”identification keys”. Starting at the first couplet enables the taxonomist to work their way through the key to finally identify which species they are working with. With experience most taxonomists can dispense with much of the key. See box below for an example of a key. More recently interactive keys have begun to become popular. With such computer based keys it is possible to identify species without the process of proceeding from couplet to couplet. This is of particular advantage when working with damaged specimens when some characters important for the species confirmation may be damaged or missing.
Recent developments in sequencing of DNA and RNA has enabled a barcoding technique to be developed. There is an international consortium working on barcoding the fauna of the Arctic, PolarBoL. By sequencing parts of the genetic code of an animal (or plant) and comparing to a database it is possible to identify species without referring to morphological characters. Particularly useful with damaged specimens. In addition this technique has revealed the presence of cryptic species, species that morphologically are identical but which have distinct genetic lineages.
Hence working with such animals requires the combined effort a numerous specialists.