Snail and Polyp ID

[Delphinus]

Hydroids are much smaller than yellow polyps. Although they look similar there's really quite a difference of scale. The hydroids look like litte palm trees (longer stalk) and then the "pom pom" is only a couple millimetres in diameter.

Not all cowries are benign. I have one that resembles a tiger cowry (but isn't) and is a soft coral muncher. But money cowries (yours is definitely a money cowrie) are benign. They come in as hitch-hikers occasionally but you can also actually buy them from time to time as clean up crew.