The Egg cowrie, (Ovula ovum) is a marine gastropod mollusk in the family Ovulidae, known as the false cowries or allied cowries. Technically they are not cowries per se but because of their similarity to cowries they are commonly known as cowries.
The shell of the egg cowrie is egg-shaped on top and is snow white with a shiny surface. The aperture on the bottom has teeth on one side only whereas true cowries have teeth on both sides of the aperture. The interior is a dark brown purple color.
The shells of the egg cowries reach 12 cm in length. In the adult the mantle is covers the entire shell and is black with raised yellow tubercles and white spots. The juvenile resembles a toxic species of nudibranch. Unusually the mantle is kept out most of the time, even during daylight.
IN THE WILD
The egg cowries are mainly seen out at night, usually on soft corals but occasionally are seen out during the day. There is evidence that they are territorial and that they return to the same hiding place just before sunrise.
The egg cowrie is found across the Indian ocean and in the west Pacific. The are found from 1 meter to 20 meters in depth. They are usually found in sections of the reef or shore that have a plentiful supply of soft leather corals.
The egg cowrie feed on soft corals, and are often seen feeding on leather corals.
Egg cowries reach sexual maturity at approximately 7 cm in shell length, at approximately 1 year of age. They are not hermaphrodites and mating usually takes place in the summer months. The eggs are laid on a hard substrate and there is evidence that the laying of eggs is synchronized with the moon cycles. The images below show a specimen in the process of laying eggs. This recorded on the 27th December 2020 off Dar es Salaam with a water temperature of 29 C.
Once the eggs hatch they become free swimming veligers and eventually develop into adults.
The shells are collected in some areas for sale to tourists but hopefully the restrictions in place regarding the transportation of shells will reduce this trade.
They are not reef safe and being nocturnal are unlikely to add any value to a tank. They feed on soft corals and possibly some species of anemone.
EGG COWRIE CLASSIFICATION
- The Reef Guide fishes, corals, nudibranchs & other invertebrates: East and South Coasts of Southern Africa by Dennis King & Valda Fraser