Know your fauna: shells

This post is also available in: Dutch, Papiamentu.

Common purple snail (Janthina janthina)

Janthina janthina

Janthina janthina

Rare blue / purple

In 1758 Linnaeus gave the scientific name Janthina janthina to a tiny and very delicate purple / blue snail shell and its snail inhabitant. The popular names for this species, which occurs in warm waters worldwide, range from ‘Purperen’ or ‘Paarse zeezeiler’ in Dutch to Common purple snail in English.

The animal is not rare, but the color of the shell it produces certainly is. There are very few naturally blue / purple shells in the world, making this species quite striking, as small as it is. Especially if you have the possibility to observe Macro shots of the shell in question. Than it quickly becomes clear how very finely patterned the shell is. The thin rounded shell of Janthina Janthina can be up to 3 centimeters wide and about 4 centimeters high and is so fragile that a happy finder must handle it very carefully.  A too heavy-handed approach reduces it to grit in seconds.
Moreover it is not only the shell which has the particular color, the snail itself is violet colored and the animal has a long cylindrical snout with a mouth on its head.

Historical drawing depicting the bubble-raft

Historical drawing depicting the bubble-raft

Floating snail

This particular purple snail is a real “world citizen”. It doesn’t live on a permanent location in the sea, something many snails do, but travels from one spot to another. The name already indicates its behavior but it’s the way the animal moves over the sea surface which is very special. The animal floats on the surface of the sea and its floating ability is due to a kind of ‘raft’ of air bubbles which the animal binds together with a type of mucus containing chitine. This is produced in the tissue of the foot (located at the underside of the snail) by the animal itself. The snails do not swim but float by means of the raft of bubbles, which they can only produce at the surface of the sea.
Under the influence of sea currents and wind, the animal travels on the sea surface while searching for food in the form of plankton and mainly juvenile jellyfish, such as the Portuguese Man of War, which also floats on the surface.
It’s because the Janthina Janthina is so sensitive to wind, that the chances of finding the shells on the beach are a lot better after a period of rough seas and strong winds.

Beached specimen found in Wawaii (Wikipedia commons)

Beached specimen found in Wawaii (Wikipedia commons)

Viviparous

The Purple sailor is viviparous in the sense that the females produce eggs that hatch in the genital tract. After hatching the larvae leave the tract. The reproductive process of the snails, however, can in no way be compared to the process of mammals. Male snails have no penis. The sperm cells swim to the female, and enter the genital tract after which the eggs are fertilized.

 

 

 

 

 

Michelle da Costa Gomez

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