Description

 

Hydatina shells are bubble shaped, vividly colored, and have a sunken spire. The aperture is as long as the shell and usually comma shaped, while the columella has a callus without folds. There is no operculum. The shells are also extraordinarily thin, which warrants their common name, "paper" bubbles.

The mollusc that lives in these shells could almost be mistaken for a sea  slug. Its foot and mantle are flagrantly overgrown relative to the shell, as shown in the link below for Hydatina physis. It also represents a significant step in the evolution from a typical snail toward a full-fledged sea slug. Like the sea slug, which has completely lost its shell, the Hydatinidae molluscs depend on swimming and camouflage to defend against predators, instead of withdrawing into a heavy shell. Hydatina species are carnivorous, feeding on cirratulid polychaee worms (Rudman, 1972).

Its shell features are somewhat similar to numerous species belonging to several famiies within the informal group, Opisthobranchia, and it was formerly but no longer included in this informal group. In the classification table, compare the following: Acteonidae, Aplustridae, Haminoeidae, Bullidae, and Bullinidae families.

 

Classification

Class: Gastropoda

Clade: Heterobranchia

Superfamily: Acteonoidea

Family: Hydatinidae

 

Major Genera

 

• Genus: Hydatina
• Genus: Micromelo

Hydatina zonata (Lightfoot, 1786)
Zoned Paper Bubble
(uncommon shell, 4.7 cm)

LINK --SEE A LIVE BUBBLE MOLLUSC: