Went back to find it and had to rehost the images from my
starter system survey post, thankfully I could still edit it. I really did enjoy that system. Will be doing this again on my new survival save.
Red crystals, if there isn't any on the surface of the planet try caves. If you can't find any cave entrances and you have the upgrade, burrow into the planet with your plasma launcher.
Like, you've never found them all on a single planet?
If you post a screenshot of the discoveries pane for it I can at least tell you if the ones you're missing are likely to be land, sea, or air creatures.