Treasure of the Month: The “Dragon Worm” Mystery

Our Treasure of the Month is a single marine bristle worm: the holotype of Phyllodoce callirhynchus – the reference specimen upon which the species was originally scientifically described and defined. It was collected in August 1890 on the East Frisian Islands by Johann Wilhelm Michaelsen, the first curator of the annelid collection at the Museum der Natur Hamburg.

Bristle worms of the genus Phyllodoce are sometimes referred to as “dragon worms” because of their shimmering colours and the leaf-like appendages along their bodies. They live on the seafloor, moving in a sinuous motion between grains of sand or algae, and are active predators that hunt smaller invertebrates. To the human eye, many species in this group appear remarkably similar – slender, segmented, with fine rows of bristles along their sides.

Since its original description, no additional specimen of this species has ever been found – making it a true one-off.

Yet anyone examining the jar today will notice a surprise: later researchers concluded that this worm was probably not a distinct species after all, but belonged to the already known Mediterranean species Phyllodoce lineata. As a result, the specimen is now usually listed under this name. How does an “East Frisian” worm come to have a Mediterranean identity? This is where a story begins that reaches far beyond a single specimen.

The scientific classification of species still follows a system developed in the eighteenth century by Carl Linnaeus. The first species described within this system were predominantly European. As researchers travelled the world more extensively during the nineteenth century, they collected new organisms from across the oceans – including countless worms.

During the twentieth century, however, a practical assumption became widespread: if worms from different regions looked similar, they were likely to belong to the same species. This seemed plausible, as many marine bristle worms have free-swimming larvae capable of dispersing via ocean currents. After all, the oceans are interconnected.

Yet worms perceive the world differently from us – or perhaps more accurately, they hardly see it at all. Most species can distinguish little more than light from dark. Visual signals therefore likely play a smaller role for them than chemical cues or tactile stimuli. Consequently, striking external differences that would immediately stand out to us are often rare – many bristle worms look surprisingly alike to human observers. This is precisely what makes their identification so challenging: organisms that appear almost identical externally may turn out to be genetically distinct species. For decades, similar animals from different parts of the world were therefore grouped under the same names, often originally established for European species.

Only modern genetic methods have revealed that this picture was too simplistic. Marine worms are likely far more diverse than the roughly 12,000 currently recognised species suggest. Behind seemingly familiar names often lie entire groups of previously unrecognised species.

And so we return to our treasure: today, the East Frisian worm is usually classified as Phyllodoce lineata – yet whether this identification is actually correct remains unresolved. Is it truly the same species as the Mediterranean form? Or could this specimen represent a distinct species that has gone unnoticed for more than a century? Questions like these demonstrate why historical collections are more important than ever.

To address such longstanding puzzles systematically, LIB researchers are collaborating with genomics and annelid experts from the Senckenberg Naturmuseum Frankfurt and the University of Göttingen in the “EuroWorm” project. The aim is to re-examine European worm species using modern genetic methods, provide more detailed descriptions, and make the data openly accessible. This will create a new foundation for global biodiversity research – and perhaps one day help answer a surprisingly difficult question: how many worm species are there, really?

Until then, our “dragon worm” remains a silent witness in its jar – and a reminder that even long-preserved specimens can still tell entirely new stories.