Last week I gave you this Blaschka glass model from the Dead Zoo to have a go at identifying:

It seems as though you’ve all managed to get your eye in with the Blaschka identifications, since there was a flurry of correct answers both in the comments on the blog and on Twitter.

Those exposed gills immediately let us know that this is a nudibranch sea slug. From there I thought it might prove more of a challenge, but by looking at the physical characteristics shown it quickly became obvious what we were looking at – at least when there is a handy catalogue to look at and provide clues.

In this case, the clue lay in the scientific name of the species: Polycera quadrilineata (O. F. Müller, 1776). As you might expect, it has many (poly-) horns (-cera) and four (quadri-) lines (-lineata), making the name helpfully descriptive. At least in this instance. The problem is that the name could be much less helpful if this model depicted the same species with a different morphotype.

In fact, it seems that there has been a separate species of Polycera hiding in plain sight until very recently. The wide variety of different colours and patterns associated with P. quadrilineata has meant that the new species Polycera norvegica Sørensen, Rauch, Pola & Malaquias, 2020 was only identified in last year, because it was lumped together with its more lineated cousin (that often lacks its stripes).

Separating these species relies on finer details than just overall appearance of course – the team that identified this cryptic critter did so on the basis of detailed morphological and genetic work that you can read about here.

It does help illustrate an ongoing problem faced when dealing with historic collections though. There have been a lot of species that have been similarly split, especially since molecular methods have become so much more accessibble. When working with old specimens it’s not unusual for these little bits of scientific progress to have been missed.

I’ve grumbled about this before, but it is a particular problem that can make dealing with Blaschkas so much more complicated. Fortunately there has been some work done on trying to match some of the more distinctly fishy taxonomy used by the Blaschkas to more modern versions, but there are still some impossible examples where the Blaschkas reproduced something from a source that had little bearing on real species. I promise I won’t set one of those as a mystery object.

Probably.