With last week’s launch of the Merseytravel (UK) Walrus card, both Creative Review and The Guardian got to wondering: What is the “watery trail” that seems to link so many smart cards? Hong Kong has the Octopus, London has the Oyster, Seattle has ORCA, Wellington has Snapper, and San Francisco has the Clipper card. The Octopus was inspired by its many uses and also represents the lucky number eight, The Guardian writes, but also wonders whether smart card names in these port cities are showing a “subliminal affection for the sea.” Not all cities are on board with the maritime trend, however, and even some waterfront agencies have looked beyond the sea for inspiration. Vancouver riders rejected Starfish (and the lackluster TPass) and named their new smart card Compass. (Possibly following the example of San Diego.) New Yorkers have their utilitarian MetroCards, and Baltimore customers can use their CharmCards to get around town. And just as the Walrus card was intended to evoke the Beatles song, Boston’s CharlieCard — named after a legendary folk song figure — has a musical legacy as well. But still the fishy themes seem to prevail. Any theories?