A “monstrous and misshapen animal”

Cerataspis monstrosa, on the left, and Plesiopenaeus armatus, on the right. (Credit: Darryl L. Felder)

Have a look at these two animals. Would you think they belong to the same species? They actually do. On the left you see the larva and on the right the adult form. These two couldn't look more different and that's the reason why for over 180 years they have been considered two entirely different species. The larva was called Cerataspis monstrosa and the adult Plesiopenaeus armatus. Both were placed in very different crustacean groups although researchers over the years suggested affinities between C. monstrosa and paeneoid shrimps. However, a final placement was never made mainly due to the scarcity and extreme morphological uniqueness of the 'monster larva'.

Bracken-Grissom et al. 2012

That has changed. A few days ago researchers from Keith Crandall's lab (I believe it was at Brigham Young University at that time - Keith is now at George Washington University) published a paper with results that are currently going through the news.

The larva was only occasionally found in gut contents of fish and dolphins and a recent unexpected find of one individual in some mid-water collections provided the group with tissue suitable for DNA analysis. Based on the above mentioned affinities they also collected and sequenced reference material within the Paeneoida and more specifically one family, the Aristeidae. They sequenced five different gene regions and the resulting phylogenetic tree clearly shows that both species are actually one.

And did they use DNA Barcodes for this find? No - simply because COI failed to amplify in several attempts. That doesn't make this find less exciting. On the contrary, this study once more shows how useful modern DNA technology has become when more traditional methods (rearing in this case) can't be applied.