Nature
PUBLISHED
Sometimes in life, one butt is not enough. Just ask the peculiar branching worms, a group of marine invertebrates that have one head attached to a tree-like network of bodies and tails.
They were once thought to be a rare tryptic of bristle worms, with only three species known to science. Now, new research looking at decades-old museum specimens has identified at least ten likely new species distributed across the Indo-Pacific, the Red Sea, and New Zealand.
Branching bodies, branching trees
Combining that data with fresh specimens, they were also able to identify a whole new genus. Jumping from 3 to 13 worms is quite the leap, but for a long time we were even further off the mark.
“For over a century, the rare branching worms were all classified as a single widespread species,” said Dr Guillermo Ponz Segrelles, coauthor of the study, in a release.
“However, we have shown that – like their bodies – their family tree has many branches, each closely associated with its own sponge species and located in specific areas.”
An exciting day for one of the most unusual creatures in the animal kingdom, and a reminder of the diversity to be discovered among museum collections.
One of the reasons the true diversity of branching worms remained hidden for so long is that they live in symbiosis with sea sponges. Their peculiar branching body plan enables them to spread throughout their host, meaning even large worms aren’t visible from the outside.
Scientists figured that sponge specimens in museums would be a good place to go looking, then. But there was a catch: museums generally don’t love it if you smash their specimens apart in search of worms – no matter how many butts they may have.
Thankfully, we live in the technological age.
Many butts fit in many holes
By using cutting-edge 3D X-ray imaging technology, the researchers could build detailed cross-sectional images of sponges without damaging them. A sponge collected in 1914 from Sagami Bay, Japan, shows how the sleeping situation can get pretty crowded when dealing with branching worms.
The image shows an example of a new genus described in the study named Cladosyllis, which joins the existing genus Ramisyllis.
It's thought the specific sponge the branching worms inhabit could be what’s driven their diversification. Some species are found in shallow water environments, while others are tucked inside glass sponges 1,000 meters (3,280 feet) below the sea.
Though we’ve added another genus to the mix, all known worms are thought to have descended from a common ancestor. This means the ridiculous body plan of growing quite so many butts only evolved once, but the two major lineages have developed their own quirks in how their bodies branch.
From old specimens to new
The scientists also gathered new specimens as part of their research and looked for differences in DNA. By combining their results, they revealed how diversity can remain hidden even among animals we’ve had in museums for over a century.
“Some of the sponges hiding these worms came from the Senckenberg collection and date back to 1914,” added Dr Ekin Tilic at the Senckenberg Research Institute and Natural History Museum Frankfurt and co-author of the study.
“We were able to reveal the worms without damaging the sponges by using microCT imaging – modern techniques are helping us rediscover hidden biodiversity in centuries-old collections.”
So, from just 3 worms we arrive at lucky 13, but the researchers believe there’re plenty more many-butted worms where that came from. The search continues, and it's hoped their complex bodies could provide many clues into the evolution of symbiosis in marine ecosystems.
Let's hope the rest of them get names as cool as King Ghidorah.
The study is published in the Zoological Journal of the Linnean Society.
