Nudibranch Research - What is a species?

by Carissa Shipman, Dept. of Invertebrate Zoology and Geology, California Academy of Sciences

Did you know there are 26 different species concepts? This is just mindboggling! You may have thought the definition of a species was settled long ago, but the reality is, the concept of a species is still under intense debate. The most commonly accepted and taught definition of a species is “a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups”.

This question is extremely relevant to my graduate project, which is looking at the diversity and relationships of nudibranch sea slugs in the family Dotidae from the Indo-Pacific and North Atlantic. For my project, I am describing five new species from the Indo-Pacific and another from South Africa, originally thought tobea N. Atlantic species. How do I know these are distinct from all other sea slugs ever named and described?

Well, since the specimens used in my project are no longer living, I first look at living photographs of the slugs, which will most of the time help me determine whether the species I am naming and describing is in fact completely new. In cases where it is not clear whether the individual in the living photograph is new, we compare its photo to the description of the species most similar to it…