A blue whale is as long as 16 school buses, or something like that. The most giant of the giant clams was 18 metres across. Southern elephant seals are enormous, but well, not as enormous as oarfish. 

From the biggest whale sharks to the toothiest great whites, the ocean is full of mysteries and tall tales (get it? you get it), but which marine myths hold up and which are mainly nonsense? Until now, it's been hard to know for sure. 

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Image: McClain et al

The ocean is a big place and most critters don’t wash ashore when they die. And even when they do, it's easy for them to appear larger or longer than they really are because of the way that biological tissue decays.

Biologist Craig McClain had enough of outlandish claims about mammoth marine life (blue whales are long, but are they 16 school buses long?), so he decided to do something about it. Together with five undergraduates and a small army of collaborators, he went about looking for every published record of the ocean's heavyweights. That meant museum specimens, news clippings, scientific journal articles and even items for sale on eBay. The resulting paper – as well as its data – is free to explore.

It's not just useful information for marine scientists and for journalists who are keen to offer comparison points when writing about these mythical creatures. In building up his database of measurements, for example, McClain discovered that octopuses appear to be shrinking. That is, the largest giant Pacific octopuses (Enteroctopus dofleini) known today seem to be smaller than those recorded in the 1800s. Could pollution or climate change be to blame?

Deep-sea ecologist Andrew David Thaler, who helped with the giant isopod part of the study, discovered that males are, on average, five centimetres longer than females, and that their reproduction happens seasonally. Nobody knew that before.

Blue whales by the way? The record, according to McClain's research, is 108.3 feet (33 metres). That's roughly two-thirds the length of an Olympic-sized swimming pool.

Here's what we want: a giant-sized version of the infographic above, so we can hang it on our walls and revel in the accurate magnitude of our planet's oceanic leviathans.

Top header image: Extra Zebra, Flickr