Algae ID please

[dwag1122]

Anyone know what this is? It’s a teal color in person and does not scrape off very easily. The only place it’s growing in the entire tank is on this shell.

 

[Dburr1014]

Anyone know what this is? It’s a teal color in person and does not scrape off very easily. The only place it’s growing in the entire tank is on this shell.

Could be coraline, they come in many colors.