The end of the crinoid project...for now

Hello everyone, it’s Mimi again! I’m back for one more blog post before the end of my summer student fellowship at WHOI. It’s quite bittersweet and surreal to see all of my work culminating into one final presentation, poster and now a manuscript. Kirstin and I have been working in the past month to turn my WHOI report into something we can submit for publication, most likely to the journal Invertebrate Biology (which is super exciting!).

To recap, the main purpose of this project was to be the first people to ever characterize the larval development of the stalked crinoid species, Bathycrinus carpenterii. In the end, we found that  the overall development process of all crinoids is pretty much the same, following the same phase progression from cystidean to pentacrinoid to juvenile. However, we also noticed that there are a few key morphological differences, most notably the discoidal proxistel.

The discoidal proxistel in Bathycrinus carpenterii.
Photographed at 35x magnification.

What is the discoidal proxistel, you ask? Well, it is the uppermost section of the stalk, right below the head where the segments are much thicker than the remaining columnals of the stalk.

This section appeared to be distinct to Bathycrinus species, as it was not present in other species of stalked and unstalked crinoids we evaluated. This structure may have adaptations to the deep-sea, including flexibility when feeding while remaining attached to a substrate. Additionally, B. carpenterii individuals have the ability to lose their head in stressful environments, meaning that the discoidal proxistel must be highly developed in order to eventually regenerate the head.

One final question we pondered was, are cystideans and pentacrinoids actually larvae? A physical metamorphosis usually separates the larval form from the juvenile form. However, for cystideans and pentacrinoids of B. carpenterii, there did not appear to be any sort of dramatic transformation, so we couldn't conclude that they underwent a metamorphosis. For this study, we decided that we would follow the previous classifications of cystideans and pentacrinoids as larvae (similar to studies on unstalked crinoids), even if there was no metamorphosis. This is an area that could use more research, but it was definitely interesting to think about.

And I guess that’s it! I hope you all enjoyed our journey, learning about Bathycrinus carpenterii.

Thank you to Kirstin for opening my eyes to the world of crinoids, and the arctic deep-sea, and a big thank you to the WHOI Summer Student Fellowship program. I hope I can be back on the blog someday in the future, but for now, I’m headed back to school for my senior year of college.

Until next time!

PS-Keep an eye out for our paper if you want to know more!