Purple Sea Snail (or Common Janthina)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Janthinidae, Genus: Janthina, Species: J. janthina · Janthinidae (Purple Sea Snail family) · Gastropod (univalve); globose-conical spiral shape.
Species
Janthina janthina
Shell Type
Gastropod (univalve); globose-conical spiral shape.
Family
Janthinidae (Purple Sea Snail family)
Size
Estimated at 15-20mm (0.6-0.8 inches). Adults typically range from 20mm to 40mm.
Color & Pattern
Distinctive bicolored appearance: the base/underside is a deep violet, while the spire and upper surfaces are a paler lavender or silvery-white. This is an example of countershading.
Rarity
Uncommon as a beach find. While biologically abundant, they are rarely found intact because their shells are extremely fragile and usually break in the surf.
Habitat
Pelagic/Neustonic; they live at the surface of the open ocean, hanging upside down from a raft of bubbles.
Geographic Range
Circum-tropical and circum-subtropical; found in warm waters of the Atlantic, Pacific, and Indian Oceans.
Description
A beautiful, paper-thin, globose shell with a short spire. The shell is lightweight and translucent to allow for buoyancy. It lacks an operculum and has a large, thin-edged aperture.
Key Features
Violet-purple coloration, extremely thin and lightweight shell, and the absence of an operculum. The countershading (darker on bottom, lighter on top) is a diagnostic trait for surface dwellers.
Collector Value
Highly desirable due to their vibrant color and fragility. While common in the open sea, beach-collected specimens in good condition are prized by collectors. Estimated value: $5-$15 USD.
Condition Notes
The specimen appears largely intact, which is rare for this species. It shows some minor erosion and possible sun-bleaching on the apex. Collectibility grade: Fine.
Interesting Facts
These snails are blind and cannot swim. They create a 'bubble raft' by trapping air in mucus with their foot. They are specialized predators that feed exclusively on siphonophores like the Portuguese Man o' War.
Ecological Role
Specialized predator that helps control populations of venomous siphonophores. They are protandrous hermaphrodites, starting life as males and transforming into females.
Similar Species
Janthina globosa (more rounded, narrower aperture) and Janthina exigua (smaller, with deep striations/grooves).
Beach Finding Tips
Look for them after strong onshore winds or storms, especially when 'Blue Bottle' or Portuguese Man o' War jellies wash up, as they travel together in the same currents.