This is Tritonia diomedea, who, by an amazing coincidence, happens to be in the news today:
"Tritonia is one of the testing grounds for a lot of ideas for how nervous systems work," says Wyeth. "Field work with this organism is helpful because it gives you a good idea of how to set things up in the lab."
[T]hey respond to odors and other sensory cues by initiating beneficial navigational behaviors, including escaping from predators by swimming up into water currents that hurl them (un-sluggishly) end over end downstream and away from harm, as well as crawling aggressively (for slugs) upstream to breed and feed. The observations also correlated with earlier studies suggesting that sea slugs flatten out their bodies to reduce drag when they encounter strong water currents, a behavior that helps them avoid being swept away....
The observations that sea slugs navigate with respect to water flow and direction based on odor and other cues will inspire further studies of this behavior and aid scientists studying the nerve cells involved in navigation, an important problem every animal faces.