Notice the attractive beaded ribs on its eight plates and the impressive setae (stiff bristles) around its margin:
Meet
Mopalia porifera! This is the first time that we have seen
this species. It can be distinguished from other chitons
in the genus
Mopalia in part by the three rows of alternating, sparse setae,
which are especially prominent at the spaces where the plates meet.
This individual was 20mm long.
Mopalia porifera is primarily a southern species found from Baja California, Mexico, to central California. We are aware of only a handful of records of this species from north of Point Reyes (museum specimens all collected at Dillon Beach in 1947 or 1974).
Because this chiton might be rare in this area, we returned to the site to look for the chiton again (for more photos) and to see if there were other individuals.
After a little searching, Eric was able to relocate the chiton. Although it had shifted its position, it was on the same rock. The shell sculpturing is quite striking:
We were also able to find a few more individuals. They were smaller than the first chiton, and slightly different colors, but you could see the same beaded sculpturing on the plates and the prominent bristles along the margins:
It was wonderful to see a new species of chiton! Kudos to Eric for spotting it and recognizing that it looked different, and many thanks to Anthony for confirming this species identification.
5 comments:
Do you know if Mopalia porifera got its species name because the texture of the bristles and margin look a bit like sponge, or whether it just eats sponge?
Hi! I was wondering about the species name, too! It seemed a little odd that the name might refer to a sponge, even though that's what you might think initially because Porifera is the name for the phylum that includes sponges.
Eric found the original species description and it in Pilsbry (1893) refers to "pores" along the girdle -- he even illustrates them. The direct quote is "...having a small pit or pore at each suture...sometimes some of the suture pores bear large hairs, curling outward." (I can append the drawing to this post if it would be interesting to you or other NHBH readers.)
Eric and I both think it's possible that Pilsbry was looking at a chiton specimen in which the setae were broken off and so the pores were insertion points for missing setae. We can't see the aforementioned pores on the live specimens, but Pilsbry's drawing matches the placement of the setae exactly. If this is what happened, it's a bit unfortunate that the species name currently refers to a feature that might not be that relevant to the identification of the species as a whole. But I suppose it's interesting history and it spurs you to think about how original descriptions of species might be misleading if based on only one or a few specimens. (Note that in the small grayer chiton in this post, you can see that some of the setae are missing, so they must be damaged occasionally.)
I was wondering about what a good common name for this chiton might be, and I always think it's helpful when there is a direct parallel between the scientific name and the common name. But in this case, I don't think using "porifera" makes sense. So we'll need to come up with a useful common name. Pilsbry describes the color of the chiton plates (or valves) as "olivaceous" -- that seems like a perfect description for the first chiton Eric found. He likes the idea of calling it the "Olive Mossy Chiton."
Jackie
Hi, Another beautiful sea creature. Congratulations on finding and Id-ing these Mopalia porifera after its not having been seen for 73 years north of the Pt. Reyes area. I am wondering what that pinkish substrate is in the 2nd set of photos that the chiton is standing/resting/posing on?
Vishnu
Hi, Vishnu!
The pink crust in the photos is a bryozoan. I'm not sure which species, but crustose bryozoans are generally identifiable by their sandpaper-like texture (or appearance). [Some references call them lacy crusts, but personally I don't think of them as "lacy."] Bryozoans are hard, rather than soft like a sponge or tunicate (sea squirt). And you can see hundreds/thousands of little "compartments," which are the individual zooids that make up the bryozoan colony.
Jackie
Thanks Jackie, I really appreciate the thorough answer! What an interesting history behind the name - taxonomy is so fun!
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