What’s inside that sea urchin?

April 20, 2023  

Hello! It’s been an exciting few days for animal spotting! Just in one day, we saw between 5 and 10 seals! We think they are Crabeater seals. We also saw Adélie and Emperor Penguins and surprisingly, both swim differently. Adélie penguins will jump out of the water and dive back in, but Emperors will bob their heads out of the water. It’s amazing to see! However, the best vertebrate we have seen so far is the Antarctic Minke Whale. This individual swam up to the surface so we could see the dorsal fin and a white spot on the side.

But now I will talk about animals with a different kind of spine than vertebrates. Sea urchins (or echinodudes as I like to call them)! For my research, I study molecular genetic pathways in sea urchin embryos to see how they grow. So, I am very interested in learning more about their development. For the species I study in the Atlantic Ocean, the offspring will undergo indirect development (from embryo to larval stage to juvenile stage) in the water and not in the parent. However, since I have been here, I have seen sea urchins brood their young instead. It turns out that many Antarctic echinoids go through direct development where the offspring will skip the larval stage and develop straight from embryos into juveniles. This is very unusual in the sea urchins that I am familiar with so you can imagine my excitement and slight confusion when I found at least 20 tiny juveniles in the brood pouches of adult urchins. Depending on the species, the juveniles can be found either inside the female in brood pouches or found outside on the test, protected by spines. A possible reason why brooding is more common in Antarctica is that the water conditions are too harsh and cold for indirect development. This way more juveniles will survive, but this leads to different implications for gene flow, migration, and speciation.

More interesting organisms we found inside sea urchins include parasites. Most of the time, there are parasitic marine worms, but we found a parasitic copepod! It was shaped similar to a pair of lungs, but it was light pink with orange veins. When it popped open, more copepod juveniles spilled out! I have never seen anything like that before and that was the highlight of my day. You can learn so much about an organism by looking at its internal anatomy including ecological interactions, development, and diet. Though sea urchins look very simple from the outside, there is so much more to learn!
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Sammie Schreiter
University of North Carolina Wilmington