Passage IV

Surf’s Up

[1]

Snails from the family Janthinidae spend most of their lives upside down, “surfing” the ocean’s surface under a cluster of air bubbles they create themselves. These “bubble-rafting snails”（janthinids) drift for miles, moving up and down, feeding on jellyfish and other floating prey. [A] They use mucus to create a small raft of tiny air bubbles, permanently attached to the bottom oftheir bodies, which makes them float in that way. In 201 1, University of Michigan graduate student Celia Churchill published a paper that explains how the bubble rafters’ incredible way of life evolved.

[2]

Churchill and her team began their research by analyzing and comparing the DNA of several snail families determining the ancestral lineage of bubble-rafting snails. [B] Churchill, who found in her surprise that bubble rafters are most genetically similar to wentletraps, a snail in the family Epitoniidae. [C] Wentletraps live on the ocean floor, they are creatures that feed on coral and sea anemones, and rarely, if ever, come up to the water’s surface. These snails use mucus to bind their eggs together into long strands or egg masses that trail behind them as they glide across the ocean floor. Churchill asserts that is the genetic precursor to bubble rafts.

[3]

According to the biologist, air often gets trapped in the egg masses of female wentletraps, forming small air bubbles. At one point, a wentletrap must have created enough bubbles to cause her to float to the ocean’s surface. Given the abundance of jellyfish and other foods on the surface, creating air bubbles and floating—became a survival advantage.

[4]

Churchill argues that though the ability to make bubbles on purpose didn’t evolve quickly, while certain lineages of wentletraps did develop this habit. [D] These exceptional snails gave rise to the handful of bubble-rafting snail species known today. Churchill, in explaining how a few bottom-feeding wentletraps became janthinids skimming the ocean’s surface, has answered the question of how some snails became surfers.