Siphona urbana or geniculata?

In Andersen’s 1996 book “The Siphonini (Diptera: Tachinidae) or Europe” he made several changes to the names of Siphona spp., which have proved a bit confusing. The changes (and subsequent reversions) illustrate a few nice aspects of modern taxonomy and so I thought I would write a little piece on what happened.

Every species is based on what’s called a type specimen – ideally a specimen that the author considers to be the archetypal individual, which he uses to describe what the species looks like – a holotype. Later on if anyone wants to revise a group or they want to be absolutely sure of their identification they can hunt down the holotype and compare it to their own specimens, safe in the knowledge that the holotype is the definitive example of the species. In fact I have at times joked that the only ‘correctly’ identified specimen is the holotype – anything else is just an opinion!

When Andersen researched Siphona for his book he examined the types and noticed that actually what we had all been calling geniculata did not match the type specimen. When he examined all of the types he came to the conclusion that what we knew as geniculata should actually be called urbana and what we called cristata should be known as geniculata. This is not as unusual a situation as you might think because types are often hard to examine (being locked away in far-off museums) and people are fallible and they assume that they know what they are talking about!

Siphona geniculata and cristata are very common flies and it was quickly noticed that such a confusing change of names would cause massive problems for workers in the group. In 1999 Tschorsnig, Herting & O’Hara petitioned the International Commission on Zoological Nomenclature (ICZN, the body that defines the rules of naming and arbitrates on nomenclature in animals) and asked them to agree to redefine geniculata by reallocating a new type specimen to it. Their argument being that, although Andersen was strictly correct, the old names should be retained due to common usage. After much debate and time for reflection, in 2001 the ICZN voted on and decided to accept the suggestions.

The lectotype of geniculata was officially replaced by a new type specimen (neotype) held in the Museum of Lund University, labelled ‘Sk. Dalby, O. Molla, 21.VII.1989, leg. R. Danielson’. This action allowed cristata to be reinstated and we returned, full circle, to the situation prior to Anderson’s shake-up.