Wednesday 25 January 2017

Striped Bubble Shell

Image: Sylke Rohrlach
Hydatina physis
What is a shell? Armour? Home? Laborious burden? How about fashion accessory?

You'd think that a nice, sturdy shell would be something that a keen, life-loving snail would want to keep a firm hold on. But, clearly, not all snails agree. That's why we have so many slugs.

Image: crawl_ray
The Striped Bubble Shell, also known as the Green-lined or Brown-lined Paper Bubble, is another example.

They still have a shell but, as the name suggests, it's very thin and fragile. It's not quite as fragile as a bubble or paper. It won't pop at the point of a pin. But it is so paper thin it's translucent! So there goes the armour.

Image: Ken-ichi Ueda
The body of the snail spills out of the shell, all gorgeous, ruffled mantle and tiny, cartoon eyes. It looks amazing, with all that pink and purple edged with bright, electric blue. That's why they're also known as Rose Petal Bubble Shells.

The shell only reaches about 5 cm (2 in) long, which is so small that the snail can't even fully retract into it. So there goes the home.

Image: Sylke Rohrlach
Despite what seem to be obvious shortcomings in the shell department, the Striped Bubble Shell is successful enough to be found in tropical waters all over the world. They've gone global! Or at least circumglobal.

They like sandy areas with large rocks and boulders dotted about. The sand is important because Striped Bubble Shells can burrow into it when they want to hide from predators. And they need to do that since, through a process of elimination, we've worked out that that shell is basically a handbag.

Video: liquidguru

Striped Bubble Shells seem to be specialised hunters of cirratulids, also known as Hair Worms or Spaghetti Worms.

These worms burrow through the sand or hide in rocky nooks and crannies. Safe in their hiding places, they extend their tentacles to find detritus to eat.

Image: Sylke Rohrlach
Except they're not safe in their hiding places at all. Striped Bubble Shells have a long oral tube with jaws and teeth at the end. Basically, they have a worm for a mouth, and presumably they use it to snatch the worms from within their burrows.

Sometimes, even a fashion-conscious bundle of rose petals needs to set a worm to catch a worm.

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