Beach Enigma

Came across this plant (?) at low tide on the beach at Spanish Banks.

Do you have any idea what it is?

 

Reminds me of the armor created by caddisfly larvae:
https://www.researchgate.net/figure...dation-experiments-A-Leaf-case_fig1_251567500

Or polychaete worms, who deploy similar style:
Genus Diopatra · iNaturalist Canada

Note location of most recent observation:
Diopatra from Trincomali Channel, Capital, BC, CA on June 16, 2022 at 02:22 PM by Catiemac. Lowest tide. In mound that “May” have been housing a moon snail · iNaturalist Canada

 

Thanks for these: very interesting, and similar, although neither seem to have the petal-like forms of my example.

 

Dimensions of your find?

 

The "florets," for want of a better word are about 1/2" in diameter.