Is the middle Cambrian Brooksella a hexactinellid sponge, trace fossil or pseudofossil?

What was Brooksella: Was it truly a jellyfish that would be important for middle Cambrian marine ecosystems, a time when animals were originating and diversifying for the first time on Earth? Or was Brooksella just preserved gas bubbles? Or maybe it was a type of bulbous algae? Or a glass sponge made of opaline silica?