If you are walking near the muddy shores of any of our tidal estuaries it’s hard to miss seeing the mud whelks. They are there in their thousands. These slow moving mud-coloured snails have elongated shells with many spiral whorls. They crawl along the surface grazing on microscopic algae and the tiny decaying fragments of plants and animals (detritus). Females lay gelatinous egg-strings and there is a planktonic larval stage.

The most common local species is the Sydney Mud Whelk (Pyrazus ebeninus). Although first collected in Botany Bay on Captain Cook’s arrival, it ranges from Queensland to eastern Victoria, so its common name isn’t terribly accurate. Another common name for this snail is even more far fetched, Hercules Club Whelk. It does look a bit like a club because of its widely flared mouth aperture but is hardly big enough for Hercules. It only grows to 110 mm.

The Sydney Mud Whelk creeps around on the mud flats near the high tide mark. It can spend long hours out of water because, like land snails, it has a fleshy cavity inside its shell that functions as a lung.

A close look at any midden near the muddy parts of our estuaries will show how important Sydney Mud Whelks were in the diet of the original Australians. Sometimes they got two seafoods at once since oysters often attach themselves to the shells of the whelks and can grow even larger than their hosts.

The other common species in our area is the Small Mud Whelk (Batillaria australis, or Velacumantus australis in older references). It is usually not as numerous as the Sydney Mud-whelk and prefers more vegetated areas such as seagrass beds and the edges of mangrove forests. It only grows to 45mm and the mouth of the shell is not widely flared.

The Small Mud Whelk is host for the intermediate stage of a trematode parasite, the fluke (Austrobilharzia terrigalensis). Sea birds are normally the host for the adult stage. The free swimming larvae of this parasite occasionally burrow into human skin causing what is known as bather’s itch or pelican itch.