The next annelid group that is part of the MeioSkag project we will explore is the family Protodrilidae with at least 36 species. It is a nice example on how important molecular data are in not only understanding their evolution but also their taxonomy. Taxonomy is one of the oldest biological disciplines and in a non-scientific way has already been done for the beginning of humanity. As humans we like to label things and this includes animals, plants, mosses and so on. However, the scientific practice of naming species only developed a couple of hundred years ago accumulating in the ground-breaking work of Linne. However, since taxonomy has developed further, both methodologically and conceptually. Nowadays, the taxonomy shall not only reflect high degrees of similarity but also agree with the relatedness of the investigated species. This is where the case of Protodrilida becomes relevant in the form of a study investigating the relatedness of many species of Protodrilidae using molecular data instead of morphological data.

Protodrilidae resemble strongly the species of Protodriloidae but are different from them in that the palps have an internal canal and are clearly set a part from the head (like in Saccocirridae). Hence, the head consists of these palps, a mouth and the nuchal organ at its end. Some species also possess eyes. The head is followed by about 20 to 70 segments and the animals are no longer than 15 mm and as small as 2 mm. They are always very slim. The anterior segments can some times be hard too differentiate so that they appear as being merged together. The body does not bear chaetae but different glands such as epidermal or cocoon glands, which are taxonomical important. Moreover, the funnels to release sperm are restricted to specific segments and this is specific for each species. Hence, one can see that there are not many and often subtle differences between the species. Accordingly, based on morphology only two genera were recognized Protodrilus and Astomus. The latter lacks a gut and mouth and comprises only one species, while the genus Protodrilus comprises all other species.

A study comprising both morphological and molecular data by Martínez et al. (2015) did find now that Astomus is deeply nested within the genus Protodrilus. Hence, the genus Protodrilus does not reflect the relatedness of the species to each other but “only” that they are morphological more similar to each other than to Astomus. Hence, this is not a good naming solution. There would have been two possible solutions to this problem. The first one would have been to include the species of Astomus into Protodrilus and essentially having all species of Protodrilidae into only a single genus, with one of them showing clear morphological differences. The other solution would be to split the genus Protodrilus into several genera with many of the genera lacking clear morphological differences to each other. Categorical levels like genus, families, order and so on are mankind and are not truly reflected in any biological parameters. Different genera, families, orders and so on can have different numbers of species, different evolutionary ages or different degrees of morphological differences. Accordingly, there are no rules for such cases in the Zoological Code of Nomenclature and it is up to the scientific community and the authors how such cases shall be handled. Martínez et al. (2015) decided to split the genus Protodrilus into a total of five genera. One of the new genera, Lindrilus, has also a Norwegian connection as it was derived from Norwegian mythological creature Lindorm. Interestingly, the type species of the genus, Lindrilus rubropharyngeus, had no Norwegian record until the first results from a recent Master project and the MeioSkag project.