How do you identify them?

Drawing of the underside (ventral surface) of the gamasid mite <i>Arctoseuis haarlovi</i>. Taken from Gwiazdowicz  D.G., Teodorowicz E. & Coulson S.J. (2011) Redescription of <i>Arctoseius haarlovi</I> Lindquist, 1963 (Acari, Ascidae) from Spitsbergen, Svalbard. Entomologica Fennica. 22;140-148.

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.Fig. 1 How some of the identification characters appear under the microscope. Here are some features on the body surface used to identify <i>Zercon andrei</I> and <i>Zerconopsis muestairi</i> as seen through a good microscope.<br />Taken from D.J Gwiazdowicz, S.J.Coulson & M.L.Ávila-Jiménez. (2009)<br />First records of <i>Zercon andrei</I> Sellnick, 1958 and <i>Zerconopsis muestairi</I> (Schweizer, 1949) (Acari, Mesostigmata) from Bjørnøya. Norwegian Journal of Entomology 56, 117–119.

Example of an indentication key for a juvenile stage (deutonymph) of the mite genus Thinoseius occuring in Svalbard.

(Taken from Gwiazdowicz & S.J. Coulson. (2010) Phoresis of the duetonymphs of Thinoseius spinosus (Acari, Eviphididae) on the calliphorid dipteran Protophormia terraenovae on the High Arctic island of Spitsbergen (Svalbard) including a key to deutonymphs of Thinoseius. International Journal of Acarology 36;233-236.)

There is a problem in the determination of deutonymphs which differ significantly from the adult specimens. Thus far there is no key to determine the developmental stages of the genus Thinoseius and the aim of the key presented below is to fill this gap. Chaetotaxy, symbols and the numbering system of setae on the dorsal side are after Evans (1963), Lindquist and Evans (1965).

 

1. Setae j1 at least twice as short as the longest dorsal setae ................................................................2

Setae j1 longer or slightly shorter than the longest dorsal setae ............................................................3

 

2. Setae j1 are the shortest setae on the dorsal, Z4,Z5 short, j4, j5 are the longest ............................ .......Thinoseius setifer Takaku, 2000

Setae j1 are not the shortest setae on the dorsal, j4, j5 are shorter, whereas Z4 and Z5 are the longest setae ....Thinoseius sawadai Takaku, 2000

 

3. Setae j1 are the longest setae on the dorsal .....................................................................................4

Setae j1 are not the longest setae on the dorsal, j4, j6 are longer ............................................................Thinoseius occidentalipacificus Klimov, 1998

 

4. Posterior of sternal shield round, z1 the same length as the majority of the dorsal setae ..........................5

Posterior sternal shield with a sharp, spiky tip, z1 shorter than the rest of dorsal setae ...............................Thinoseius kargi Hirschmann,1966

 

5. Setae j2 shorter than z1, setae j3–j4 the same length as setae J3–J4, setae in row z–Z the same length as in row j–J .....Thinoseius berlesei Halbert, 1920

Setae j2 longer than z1, setae j3–j4 longer as setae J3–J4, setae in row z–Z distinctly longer than in row j–J..Thinoseius spinosus (Willmann, 1939)