Bubble Shells

By Alex Scott

bubble shell gastropod

The snail and the slug often get a bad reputation in the animal world for being slow or slimy or just ugly. But the class of invertebrates known as Gastropoda, which contains snails, slugs, and limpets, is second only to insects in its number and diversity of species in the animal kingdom. Coming in a myriad of shapes, sizes, and colors, gastropods are a vast group of animals that fulfill a variety of important roles in almost every ecosystem around the world. And one bright pink gastropod in particular, given the scientific name Hydatina amplustre, also fulfills another critical purpose: adding to the collection of avid beachcombers.

hydatina bubble shell

Widely distributed throughout the tropical Pacific and Indian oceans (from Hawaii to Africa), H. amplustre is most often found in coastal, rocky tide pools. This species is a member of the family Amplustridae, which is a type of heterobranch sea snail. “Like nearly all heterobranchs, they are simultaneous hermaphrodites, meaning each snail is both male and female at the same time,” says Cory Pittman from Sea Slugs of Hawaii. “The animals are nocturnal, burying themselves in sand during the day.” These tiny animals usually live no longer than a year and eat mostly polychaete worms living on the seafloor.

hawaiian pink bubble shells

Species in the family Amplustridae are known for their thin bulbous shells that give them the name “bubble shell.” H. amplustre is also called Royal Paper Bubble, Pink Bubble, Ship’s Flag Bubble, or Swollen Bubble Shell. This thin and colorful pink, white, and black shell does offer some protection from predators, but the snail also relies on distasteful chemicals obtained from its food to deter them. Two tiny black eye spots detect light and help the animals navigate.

bubble shell animal

Although marine biologists would say that the snail within the shell is the most interesting part of the animal, for beachcombers, it’s all about the outside. “These delicate and hard-to-find seashells are just as breathtaking as the translucent, dreamy, and pretty cute snail that resides within,” says Becky Reinbold, a beachcomber who has a beautiful collection of bubble shells she has found in Maui, Hawaii.

collection of pink hawaiian bubble shells

Tiny, vacant shells can be found at the highest tide line in the sand, mingled with other rubble and debris. Occasionally, the empty shells can be found in tide pools, floating on top of the water. Becky adds, “The shell itself is quite fragile and paper thin and can be difficult to find intact, making them a fun and rare beachcombing find!”

This article appeared in the Beachcombing Magazine March/April 2020 issue.

Update: We just had to share this adorable video of a hermit crab that made its home inside a bubble shell! Thanks to Autumn and Adriana R. for sharing it!

2 comments

Oh my gosh, Autumn, that must have been the cutest little hermit crab to fit in the bubble shell! Would love to see your video! You can email it to submissions@beachcombingmagazine.com if you like! Thanks! Kirsti

Kirsti Scott April 13, 2021

So cool! We were surprised to find a hermit crab residing in this shell when we went to ‘Onekahakaha Beach yesterday! I have never seen one of these before (despite seeing MANY hermit crabs in my lifetime), so off to Google I went and found this article.

A very unusual find, indeed! We had to get a video and released the little guy back where we found it :)

Autumn April 13, 2021

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