Aquamen

Pantheons include sea gods like Neptune and Lir. Superhero teams include aquatic superheroes like Aquaman or the Submariner. After the continuity-changing Crisis On Infinite Earths, Editor and Writer Roy Thomas retconned Neptune Perkins and Tsunami to replace the Golden Age Aquaman. Such marine superheroes are fascinating but would be even more so if we were told more about their physiology and psychology and about how they function at different depths.

Once, trying to touch the bottom of an artificial lake, I swam down to a level that was suddenly dark and cold with a pain in the ears so I re-ascended as fast as possible. Our heroes would be comfortable at that depth and would be able to descend further.

Poul Anderson describes this process in The Merman's Children (London, 1981), pp. 53-54. In mid-Atlantic:

the halflings wave to wind and sun, then submerge;
for their first breath of sea, they blow out, then widen lips and chest;
water enters and permeates their bodies, activating the merfolk metabolism;
subtle humours decompose water to extract oxygen;
salt is sieved from tissues;
interior furnaces counteract the cold although it is still felt (merfolk are few because they need more food at sea than men do on land);
as they descend, light decreases, then departs;
there is complete silence;
the underwater dialect of the mer-tongue comprises hums, clicks and smacks;
each halfling has an undersea "lanthorn"/lantern strapped to his left forearm (not quite Green Lanterns);
they regularly work chest and stomach muscles to equalise pressure inside and out but still feel the weight of the water;
their leader feels that he nears bottom before uncovering his lantern;
he smells rank flesh and hears or senses the movement of the kraken's gills;
with the lantern, he sees the kraken.

We need this kind of description and more in superhero comics.