Yesterday (20 February 2021) when Eric and I walked on Salmon Creek Beach, we found lots of these horseshoe-shaped gelatinous structures. There were a variety of sizes and some variations in the details of the shape, but we think it's likely they all belong to the same species. Here are several views with a ruler for scale:
Some of you might recall that we found something similar several years ago (in 2015 and 2016). We think these are the nectophores of a siphonophore called Hippopodius hippopus. This primarily southern species is not common in Bodega Bay, but yesterday we found over 50 of these nectophores on the beach in about one hour of walking.
If you're not familiar with siphonophores, don't worry. These planktonic colonial invertebrates are usually found offshore in the open ocean, so they are unfamiliar to most people. And siphonophores are fragile, so if they wash up on the beach, they're usually found in pieces. The entire colony looks quite different.
To help you envision what the colony looks like, Eric cleaned up this older illustration of Hippopodius hippopus (see below). The parts we found on the beach (the nectophores) are arranged adjacent to each other at the top. The trailing sections of the colony below the nectophores include units for feeding, reproduction, and defense.
Modified from Haeckel, E. 1888. Report on the Siphonophorae collected by H.M.S. Challenger during the years 1873–1876. In: Report of the Scientific Results of the Voyage of H.M.S. Challenger, Zoology, 28: 1–380. https://doi.org/10.5962/bhl.title.6513
For more explanations and a little more information about Hippopodius hippopus, you can review the post from 16 April 2015.
P.S. I'm interested in other
observations of this species, so if you're out walking the beach and
see one of these little "horseshoes," take a photo and send it to me!
P.P.S. I'm posting this as is, but after comparing the 2021 photos with the 2015 photos, I'm not feeling 100% certain about the identification. I'm going to look into it further and will update this post if I find that this is a different species.
4 comments:
So glad to see this post! I have been puzzled by similar things seen at Manchester 2 weeks ago on the wrack line. They looked like clear doll-shoe mules or clogs with bumps on them. I don't have a photo, but contacted my friend Sophie who does. Hopefully she will send you a photo.
Monica Schwalbenberg-Peña
Hi Jackie. These structures look rather solid and gelatinous- do they function as floats for the colony, or is there some pulsing, or movement involved?
So cool.
Thanks!
marni
Hi, Monica!
Hmmm...from your description, I'm wondering if you might have seen Corolla spectabilis -- check out this post for another gelatinous wash-ashore that might be a match with what you saw at Manchester:
https://bodegahead.blogspot.com/2020/12/not-your-typical-shell.html
Jackie
Hi, Marni,
Good question! I haven't seen Hippopodius live, so I can't speak from direct observation of a living animal. However, I've found reference to both -- i.e., that the nectophores are likely involved in both buoyancy and propulsion:
From Totton (1965):
"Sufficient buoyancy must be provided by the exceptionally thick, gelatinous mesoglea of the nectophores."
and
"In life, the nectosac is not as flat as has been suggested, but utilizes a considerable volume of water in forming a propulsive jet."
Jackie
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