Elongate Janthina Shell, Janthina umbilicata
Elongate Janthina Shell, Janthina umbilicata. Shell collected off the beach of Punta Chivato, Baja California Sur, June 2025. Size: 2.0 cm (0.8 inches) x 1.9 cm (0.5 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Phylogeny: The Elongate Janthina Shell, Janthina umbilicata (A. d’Orbigny, 1840) is a gastropod member of the Epitoniidae Family of Wentletraps and Violet Snails. The genus Janthina is one of seventy-one genera in this family, and there are eight species in this genus. They are also known as the Round Janthina Shell, the Small Violet Snail Shell, and the Elongated Violet Snail Shell. The genus name Janthina comes from the Greek word meaning violet-blue. Because these shells are free-floating drifters they are considered to be a form of holoplankton. Note, taxonomy for this species is currently in flux. The order-Caenogastropoda incertae sedis means that no one currently knows where these shell fit. The family was changed within the past decade from Janthinidae or Lanthinidae to Epitoniidae, with most family members not resembling this shell. Some sources still refer to this species as Jathina globosa (Blainville, 1822), not to be confused with Janthina globosa (Swainson, 1823). Currently, the World Registry of Marine Species (WoRMS) and MolluscaBase have accepted it as Janthina umbilicata (A. d’Orbigny, 1840). You may find other sources that disagree.
Description: Elongate Janthina Shells are thin, fragile, and globular in shape. They consist of three or four rounded whorls, looking much like a land snail. The apex is blunt and fairly low. They are sculpted with low axial growth lines. They float on the surface of the ocean, surrounded by a bubble raft. A low ridge around the body whorl, continuing as a notch at the outer lip of the aperture, indicates where the raft was attached. The aperture is large and ovate, with a straight columella. The exterior color may be blue, pale violet, or light purple. The interior may be white, or match the exterior color. These shells do not have an operculum. Elongate Janthina Shells reach a maximum diameter of around 2.1 cm (0.8 inches), though most are much smaller. These shells can be confused with the similar looking Violet Sea Snail Shell, Janthina janthina, which is larger and lower-spired.
Habitat and Distribution: Elongate Janthina Shells are a pelagic species that floats on the surface of the open sea. When winds and currents push them ashore they are often found in large groups on the sand. It may be years, decades, or centuries between these beaching events. They have a global distribution in temperate to tropical waters. They are found in coastal waters of all Mexican waters of both the Atlantic and Pacific Oceans.
Ecology and Behavior: Elongate Janthina Shells are predators that feed on zooplankton including siphonophores. haliobatids, other Janthinas, and hydrozoans, such as the the Blue Button, Porpita porpita and By-the-Wind Sailor, Velella velella. Sea birds, fish, sea turtles, and other pelagic mollusks are common predators for these shells. They are protandric hermaphrodites and reproduce sexually, with internal fertilization. They are ovoviviparous, with the eggs developing internally and being released as veliger larvae. Their engagment in any type of commensal, parasitic, symbiotic relationships has not been formally documented. They construct their bubble rafts by attaching together bubbles made by the extension and contraction of their propodium. From a conservation perspective they have not been formally evaluated however they are fairly common with a very wide distribution and should be consider to be of Least Concern.
Synonyms: Lanthina (Iodina) megastoma, Janthina globosa, and Janthina nitida.