Just to prove there is always something new to find, this weekend I stumble across special swimming snails Ethminolia. I’m always surprised how little we know about the commonest of species in Port Phillip Bay. There’s been more research done in the Coral Triangle than there has been for many of our Great Southern Reef animals. And after a few years of snorkelling northern Port Phillip Bay, we are still adding to our own list. We’ve seen many rare, poorly known or only recently described animals. Things like Sacoglossum seaslugs; Little Gurnard; Red Gurnard; Parrot Seagrass Clingfish; Oyster Blennies; Japanese Kelpfish (introduced).
Spotting and identifying flying snails
Last weekend when I was night-snorkelling at Quiet Corner I saw what I thought was a small (0.5cm) snail flying through the water. I couldn’t relocate the individual so I put it down to ‘the one that got away’. Yesterday off Black Rock I was watching an 11-arm starfish and all of a sudden, two of these leapt and swum off ahead of being eaten. So I set myself to the task of trying to photograph one ‘in flight’. Remarkably I managed to get the shot I wanted the first time I tried. For anyone interested in the technique, I’ve described it below.
I initially needed help from the marine research group to identify them as there so little written about them. Thank you to Ben Travaglini and Audrey Falconer for your assistance.
This species’ common name is Depressed Top Shell which is another example of a terrible colloquial name! Why isn’t it called ‘Southern Swimming Snail’. This is, after all, a unique endemic to our Great Southern Reef. There are a few species found locally that should be almost iconic but seem to be given little regard. Perhaps it’s that we’ve grown up thinking only the Great Barrier Reef is important.
The Wikipedia page for this snail doesn’t even mention their swimming behaviour. I’m going to call it Southern Swimming Snail as it sounds much nicer.
Identification of Ethminolia vitiliginea or Southern Swimming Snail
The species is found from Fremantle to Bass Strait and was described by Menke, K.T. in 1843. A 2022 paper by Platon Vafiadis of Marine Research Group of the Field Naturalists Club of Victoria referred to mention of swimming in 2015. It was already known that others in the subfamily Umboniinae can do this. The family is Trochidae, which are generally herbivorous or omnivorous.
What makes this animal immediately unique from outside appearance is its various appendages. It has long, tapering, hairy tentacles and eyes that jut out from below the shell. It’s also assymetrical in design. The left neck lobe is sheathed by a series of finger-like projections (see image of the animal on the sand, below) and the right is rolled up into a siphon (also visible in front of the animal, vaccuming the sand, presumably smelling for food).
How Ethminolia vitiliginea swims
The following sequence of photos over about 5/1000s captures the moment of takeoff. The distance covered was about 20cm.
Swimming happens when the snail is threatened. It extends its head far beyond the shell and flattens its foot into a paddle. It then writhes its body in rapid worm-like movements, propelling the shell forward. There is a nice video on Vafiadis’ paper that shows this in action in closer to real time. You’d be forgiven for thinking you’re seeing a worm.
Camera settings for photo
This was a hard photo to take and probably a 1:100 chance of it working. Only because the animal need to leap within the frame and the action was instant. It took only 5 shots at about 1/1000s to leave the frame. Which means the animal was outside of the shot within 5/1000s of a second.
Settings: I use a Sony XR100 in a Fantasea Underwater Housing. This photo was taken with Aperture Priority, ISO640, F11. I set the camera to High speed continuous shooting and AF-A (auto) focusing. My lights were on throughout the sequence. Then I focused on the individual, held the trigger down and began taking a series of high speed frames. I then gently nudged my stick underneath the shell, forcing the animal to jump. The shutter speed varied from 1/800 to 1/1250s.
