Scientists have discovered that a type of Arctic marine snail known as a sea butterfly gets around under water by “flying”, rather than paddling by means of a regular snail’s foot as other marine molluscs do.
According to the findings of a study recently published in the Journal of Experimental Biology, this unusual and elusive snail has wings sprouting out from the hole in its shell where normal monoped snails have just a slimy mass of muscle. The authors of the study say that “the zooplanktonic sea butterfly Limacina helicina ‘flies’ underwater in the same way that very small insects fly in the air. Both sea butterflies and flying insects stroke their wings in a characteristic figure-of-eight pattern to produce lift.”
According to the BBC, the 3mm aquatic creature also employs some of the vortex-making tactics that allow insects to stay in the air. Researchers say that the snail’s insect-like behavior is “a remarkable example of convergent evolution” in that the same trait has evolved independently in totally different evolutionary lineages.
The discovery was made by Johns Hopkins University’s Dr David Murphy along with colleagues at Georgia Tech by using high-speed video and flow-tracking systems. According to an article in Eurekalert, once the complicated logistics of getting these “fragile” molluscs over to land-locked Atlanta had been dealt with, there remained the problem of coercing the little critters to perform for the cameras – an obstacle that the researchers were able to circumvent by using an especially constructed tank that corralled them into swimming along a certain route. The sea butterflies were made to move through a restricted area of water intersected with lasers and filled with shiny particles, allowing Dr Murphy and his team to capture and track the tiny snails‘ precise movements and the flows their wings created in the fluid around them. “Using our four cameras, we make a 3D measurement of the flow that the animal produces as it’s swimming,” Dr Murphy told the BBC:
In this sort of free-swimming experiment it’s normal to take 30 passes to get three usable ones, but we got really lucky! The animals even cooperated by swimming in different orientations, so we could see different perspectives.
The findings of the study may prove important to disciplines such as micro aerial vehicle (MAV) design.