ONYX COWRIE Erronea onyx (Linnaeus, 1758) – CHOCOLATE ALL THE WAY!

Dorsal and ventral view of the Onyx Cowrie, Erronea onyx (also called as chocolate cowrie)

The first time I looked at the strikingly glossy shell reminded me of someone serving homemade chocolate! Commonly called as the Onyx or chocolate cowrie, this shell belongs to class Gatropoda under phylum Mollusca. The shell is pear-shaped with or without golden banding (often 2 or 3 bands). The underside is dark brown and terminates as black near the teeth. The teeth are orange to reddish in nature.

A resident of silty sandy substrates, seagrass meadows or coral rubbles, the lustrous shell is seen only when the mantle is withdrawn (Mantle – PALLIUM in Latin meaning robe or cloak). The shell has a very deep coating of enamel externally giving a painted appearance.

The movement of mantle from within the shell containing mucus leads to constant cleansing of the shell. When compared to other marine shells, cowries are one group devoid of any fouling organisms on it. Two lobes of the mantle extend out over the dorsal surface of the shell continually depositing enamel while protecting the shell from any kind of fouling or abrasions. Contrasting mantle and shell colours is another interesting morphology of Onyx cowries. The mantle is golden yellow speckled with black spots, white spots, white blotches and short white or bluish projections (papillae). Even predators get confused because of the swift withdrawal of mantle when touched leaving only the visible shell.

Onyx cowries feed on sponges like their other relatives but very little information is available on the food and foraging characteristics. Other food generally preferred by cowries includes coral polyps or algae.

Onyx cowries can grow from 32 – 38 millimetres in length. The species is named Onyx because the shell is shiny like an Onyx precious stone.  It is reported from depths ranging from 5-25 meters.  Onyx cowrie is a common species recorded in the coral reefs of India very specifically in Palk Bay, Gulf of Mannar, Andaman & Nicobar and Lakshadweep islands.

Onyx cowries are collected by conchologists and are sold as souvenirs or curios in coastal areas. It is reported to be eaten as food in some south East Asian countries. Key chains are popular and sold to pilgrims and tourists in places like Rameswaram and Kanyakumari in the southern state of Tamil Nadu.

 

Taxonomic Position

Kingdom: Animalia

Phylum: Mollusca

Class: Gastropoda

Subclass: Caenogastropoda

Order: Littorinimorpha

Superfamily: Cypraeoidea

Family: Cypraeidae

Genus: Erronea

Species: E. onyx

Author: (Linnaeus, 1758)

 

IUCN Status

Not Assessed (NA)

©Deepak Samuel, April 2014