The Humboldt squid (Dosidicus gigas) and the purpleback flying squid (Sthenoteuthis oualaniensis) can look very similar. If you're fishing in a location where only one of them lives (like Indonesia for Sthenoteuthis or California for Dosidicus), no problem. But in certain areas of the Pacific Ocean--oh look I have a map--their ranges overlap, so there is confusion. Panic. Mayhem. Which squid is it?
But never fear, you too can become a squid expert in three easy steps! Here's the cheat sheet:
In words: if the squid has a big photophore on its back, it is definitely Sthenoteuthis. But if it doesn't have a photophore, you can't be sure, and you have to move on to the next two items. If the skin slips and slides and bunches up easily, then it's Dosidicus. If you can't budge the skin, it's Sthenoteuthis.
Finally, if you're doing a dissection, see whether you can separate the mantle from the funnel with your hand (Dosidicus) or if you need a knife (Sthenoteuthis).
There now, don't you feel better?