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The images look like different organisms.
The first image of the yellow mass looks like egg cases of a whelk. The white growth on the shell in the second image may be a Corallina algae. Try reposting them as separate items putting the egg cases in invertebrates.
I agree with Steve. Dog whelk eggs (most likely) and on the right, a bleached Corallina
OPAL Community Scientist
Yorkshire and Humber
Lat/Lng: 50.8013, -0.0573
OS grid ref: TQ369019