A panoply of wonders awaits.
Karnak's Slaves:
This otherwise-unnamed race from an unnamed planet get a pretty raw deal: conquered and mind-controlled into servitude by scientist Karnak, they all seemingly die when he does. It's a real shame. (Weird Comics 007, 1940)
the Deadly Plants:
It's hard to say much about the so-called "Deadly Plants" of planet Vegeto, aside from the fact that they work together to capture a handful of prospective human colonists and dump them in a pit, and that for this act of moderate aggression the Red Comet dumps the entire termite population of Earth on them, seemingly wiping out their entire species. This is what we call "disproportionate response" but is in perfect keeping with the 1940s (and beyond!) view of the relative value of human life vs all other life. (Planet Comics 004, 1940)
Dhakka Snail-Men:
Every undersea race in comics needs a selection of other undersea races to have conflict with, and Neptina's Fish-Men are no exception. They are menaced by the Dhakkas, aka the Snail-Men, led by Prince Petor, who attempts to invade the territories of Amloza for no stated reason - I guess that's just what you do when you have an army and an abyssal plain to march across. Unfortunately for Petor and his ambitions, Neptina and the Fish-Men are backed up by Brad Fletcher and his Super-Sub, which are enough to decisively turn the tide.
The Snail-Men also might be some of the least like their namesake of any of the [animal]-Men we have yet encountered. They ride snails, sure, but about the only thing that they themselves have in common with snails are some pretty modest eyestalks. (Champion Comics 009, 1940)
Dragon-Lizard Men:
Encountered by detective Fu Chang as he searches for treasure on fabled Money Pit Island, the Dragon-Lizard Men are not so much guardians as obstacles on the way to wealth. The most remarkable thing about them is that if they are as Fu Chang asserts descended from the "lizard and dragons" left on the island by the treasure-burying pirates they managed to not only evolve into fully humanoid forms but also enough of a sense of shame to wear briefs over their mysterious lizard and/or dragon genitals. Nature is really amazing. (Pep Comics 009, 1940)