Plough Snails - fastest molluscs on the planet?

This is a favourite image of mine. Taken almost ten years ago on lonely Struisbai beach on the southern coast of South Africa, it's an extreme wideangle shot of a stranded medusa jellyfish being attacked by plough snails, Bullia rhodostoma.

Jos and I seemed to be the only humans on this three mile Indian Ocean beach that day but we shared it with plenty of wildlife. The vast carcass of a long-dead humpback whale attracted scavenging gulls and crows to its rotting blubber, there were lots of other birds around and the beach was littered with jellyfish thrown up by the surf.

Passing a beached blue medusa, we noticed many, what we thought to be hermit crabs, scurrying towards the hapless jellyfish. Looking closer, we were amazed to find that they were marine snails, some three or four centimetres in length.

They moved across the sand at an unbelievable rate for gastropods, 'ploughing' towards the medusa, until eventually, there was quite a crowd of them, scrabbling over each other to get at the jellyfish and piercing its outer membrane with their probosci to feed on the soft tissues.

This short video clip, courtesy of Wikipedia, illustrates beautifully the 'breast stroke' action of the large muscular foot, enabling the snail to move along wet sand at a rate of several metres per minute.

To get anything better than a record shot, I needed to get low down and close to the action, so I used a 10-22mm lens at 10mm (16mm full frame equivalent) and shot from its minimum focus distance. I had to be quick too, because that surf, which looks a long way off due to the wide angle of the lens, was pretty close and throwing waves up the beach beyond the medusa on the receding tide.

Jos's less than flattering shot of me doing this shoot demonstrates the indignity and discomfort we nature photographers must sometimes suffer in pursuit of our craft.