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Morning encounter with a benthic ctenophore

Something extraordinary happened today—I saw a benthic ctenophore!

The last time I saw one was fifteen years ago, while I was working at a marine station. Now that I live far from the ocean, such an improbable encounter is truly remarkable. I would never have thought that I would see a benthic ctenophore when I left home this morning.

But—what’s a benthic ctenophore, and how does it differ from a pelagic ctenophore?

Pelagic ctenophores

Most ctenophores are pelagic, meaning they live in the water column. They are typically transparent and have several iridescent rows (combs) of cilia that beat in synchronous waves, propelling them around.

Pelagic ctenophore
Pelagic ctenophore Mnemiopsis leidyi. Photo by me in the Wikimedia Commons.

Now, what does a benthic ctenophore look like?

Benthic ctenophores

Benthic refers to living on the bottom of the sea, sometimes on top of other organisms. These ctenophores don’t swim; instead, they crawl around and have two long tentacles with which they capture food. While they lack iridescent cilia, they are still striking.

Benthic ctenophore
Alvaro E. Migotto, Otto M. P. Oliveira. Benthic comb jelly (ctenophore)Cifonauta image database. Available at: http://cifonauta.cebimar.usp.br/media/5403/ Accessed: 2023-12-26.

This is the species that I observed at my marine station days, Vallicula multiformis. If you are curious, take the opportunity to explore more photos and videos of these animals, thoroughly documented in the Cifonauta database.

Inland ctenophores?

How did a benthic ctenophore end up in our lab in the middle of Germany?

Johannes, a colleague working with flatworms, persuaded some coral breeders to send him any flatworms they found in their aquariums.

While pelagic ctenophores look nothing like flatworms, benthic ctenophores do.

This is what we saw that morning:

Unidentified benthic ctenophore
Unidentified benthic ctenophore with a lovely pink coloration. Photo by Johannes Girstmair.

Although its tentacles were mostly retracted, they were still visible:

Tip of a retracted tentacle of a benthic ctenophore
Close-up of the tip of a retracted tentacle of an unidentified ctenophore. Photo by Johannes Girstmair.

Laboratory cultures

This encounter made me think about lab cultures. Benthic ctenophores have an outstanding developmental biology worthy of more in-depth investigations.

They can reproduce asexually by fragmenting their bodies and sexually by brooding their young in tissue pouches until the embryos hatch as larvae. But little is known about their embryonic development (see Glynn et al. 2019).

Would it be feasible to close the life cycle of benthic ctenophores in the laboratory?

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