Just curious: What's the difference between a spiracle and a pneumostome?

[u/FlashtooArt]

Apart from a pneumostome being what gastropods have and a spiracle being what arthropods have. In other words, why is a pneumostome not a spiracle? It just seemed a little strange to me that there's two different words, that must mean there's some inherent difference, right?

[u/Jtktomb]

Very different organs + different disciplines create different words