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Not bubble gum but bubble shell

By Staff | Jul 17, 2009

It wasn’t until the last few years that I began to gain an appreciation for the “not- as-glitzy” small shells. Now I find them to be an adventure of sorts. The first phase of the adventure is finding them and the second phase is assuring they will be identified properly. Frequently this adventure begins in the first foot or so of the surf, often sitting for hours sifting “shell grit” in an old metal strainer that is part of my “go shelling” bag always loaded in the back of my car. The mud flats and sea grass community on the Fort Myers side of the Sanibel bridge have become a frequent personal destination.

One of the small species I enjoy discovering is the Bulla striata, or bubble shell, named for its bubble-like shape, and delicate nature. This barrel shaped species is glossy, thin, fragile and variable in color. Reaching about two cm in length, it is found widely in warm seas. The striate bubble is cream-colored or whitish with darker brown or reddish-gray streaks and smudges of purplish brown dots. The aperture (opening) is narrow at the top, rounded at the bottom and longer than the remainder of the shell. The outer lip is thin, rounded below and arched at the top.

Unlike many gastropods, the bubble shell does not have an operculum (trap door) but the foot is well developed and like the mantle is slightly translucent. The animal can completely cover the shell when extended but likewise can retract entirely when necessary.

Bubble shells call the grassy mudflats home. As burrowers, they can take cover in mud or under seaweeds at low tide. They move like toboggan sleds, gliding across the mud surface. They are more active at night than during the day. Dinner for them is comprised of small, live, mollusks that are swallowed whole. Those that fall prey are crushed by strong, shelly plates lining the gizzard.

Bubble shells are hermaphroditic, laying jelly-like coils that contain many thousands of small greenish-yellow eggs. The egg masses may be attached to sea grass blades.

Hermit crabs are known to take up residence in bubble shells.