Dave Bonta's "Conch shell" is a single sentence built around a comparison. The thing being described is the sound you hear when you hold a conch to your ear, the hiss of the sea. Instead of simply calling it a rushing or a roar, the speaker offers two surprising images for it: a "speechless opera" and "dust in ladies' hair."
Both images are odd, and that's what makes them work. An opera without a voice suggests something grand and dramatic that has been reduced to pure breath, all the feeling but none of the words. Dust in ladies' hair is softer and more faded. It suggests old-fashioned rooms, powdered wigs, and things left to settle over time. Together they make the sound seem both theatrical and ghostly.
The speaker doesn't say how they feel outright, but the tone is curious and quietly wistful. The mood is hushed and a little mysterious, as if the shell holds a faint memory of something grand, now worn down to a whisper.