Song of the crinoid

"This is a song about a boy
A song about a little boy and his cebus 
A song about a little boy and his three cebus
The little boy had a sick cebu, a sad cebu, and a mute cebu
And also a hippo"
- "Song of the Cebu" from the children's series Veggie Tales

It's been an interesting week in the lab. As some of you might recall, my intern, Mimi, spent her summer describing the larval development of stalked crinoids in the Arctic deep sea. She used specimens I had collected in 2017 along with my German collaborators, as part of a long-term experiment in the HAUSGARTEN. At the end of her internship, Mimi produced a final report, which I then turned into a publishable scientific manuscript: "Ontogenetic development in the Arctic deep-sea crinoid Bathycrinus carpenterii." We were ready to submit to a journal - or so I thought. 

Before we submitted the paper, I reached out to two crinoid experts to ask for their input. I figured they'd come back with some small comments, and they did. But they both came back with one big comment: our specimens were not Bathycrinus.

I absolutely love when I get to correct myself on this blog, because it shows how science really happens. Mistakes are a key part of the process! I have thought a hemichordate was a nemertean, a nudibranch was a sea cucumber, and made countless other false identifications. And here's the thing - I'm good at identifying invertebrates. I have an extensive mental catalog and sometimes even annoy friends by rattling off genus names at the beach. But there are 37 phyla in the animal kingdom, and all 37 of them contain invertebrates. By comparison, the vertebrates all belong to one single subphylum. It is absolutely impossible for one person to identify every invertebrate correctly, every time - there are just too many of them. Some scientists are experts in one particular phylum or one geographic area, which is great, but it is impossible for a single person to be an expert in everything.

So if my specimens aren't Bathycrinus, then what are they? They're definitely a species of crinoid - that much I can say for sure (although after staring at my specimens under the microscope for so long, I honestly wouldn't be surprised if one of them morphed into a hippo). Well, it turns out there's only 3 species of crinoids in the waters near Svalbard, and only 2 of them occur in the deep sea. One of those is Bathycrinus, and the other is...(drumroll please)...Poliometra prolixa. 

The key difference between Bathycrinus and Poliometra is that Bathycrinus lives on a stalk its whole life - it's a sea lily - whereas juvenile Poliometra break away from their stalks and swim away. Poliometra is a feather star. (If you've never seen a feather star swimming, I recommend you check this out because it's absolutely gorgeous.)

It took me a while to convince myself that my specimens are feather stars, but it actually makes a lot of sense. The arms of the oldest specimens look pretty feather star-like, and the oldest specimens also have cirri, which sea lilies never have. Plus, the more I thought about it, the better I remembered that we had seen adult Poliometra resting on the long-term experiment when we recovered it in 2017! 

Sometimes, it feels like half my job is just answering the question "What is that?" It can be a long-winded adventure, but I'm grateful for taxonomic experts who can help along the way. Now that we have a more reasonable species identification, Mimi and I can move forward with our paper. All the results are still valid; we just need to re-do some of the text to focus on Poliometra instead of Bathycrinus. I'm excited for the next step in the project!

Poliometra prolixa on the long-term recruitment experiment
in 2017. White arrows mark stalked larval forms, and the
black arrow marks an adult. Photographed using ROV Kiel 6000