Often claimed to be shark poo, these gelatinous croissants made of mucus and a sprinkle of sand are in fact masses of eggs laid by the Moon Shell, a carnivorous snail that feeds on other shelled molluscs. On the sand flats the molluscs include the oysters seen in the photo and the whelks that lie around casually waiting for the returning tide.
If you are a keen observer of sea shells on the sand you will have noticed that some types of empty shells have a tiny neat hole usually drilled at the apex, in the ideal place for threading a necklace. The molluscs that produce these shells have a pair of shells that come together to form a shelter for the soft innards, they are known as bi-valves. The mollusc that made the hole is another type entirely, a gastropod – like the garden snail. The class Gastropoda contains a vast total of named species, second only to the insects in overall number. Moon shell gastropods are able to travel along quite efficiently by extending a big muscular foot. These active mollusc are then able to hunt the less agile bi-valves and anything else that they come across. Moon shells can be carnivorous and they are also known to feed on soldier crabs.
Molluscs have a body plan that incorporates hardened elements, usually a shell, in the case of an octopus it is a horny beak, while gastropods have a shell and a radula, a tongue structure that looks like a miniature chainsaw composed of many tiny teeth on a band that will easily saw through plant material or drill holes into shells. The moon shell will grab hold of the prey with its foot and locate the precise spot to start drilling with the aid of an acid secretion, the muscle that clamps the two shells together is disabled and the shells can then be prised open and the contents removed.
The moon shell that is commonly found on the Deeban Spit is Polinices (Conuber) sordidus
There is an illegal market for shells collected in Port Hacking with specimens selling for $10 each.
My grandson Otto calls them ghost pooh. Rosaleen