I hope this rather cute snail is transparent enough to qualify. What’s that saying, “transparency is in the eye if the beholder?”
Shiny tortoise beetles have semi-transparent ‘shields’ extending out from their thorax and abdomen.
Cassida piperata | Small Tortoise Beetle · 애남생이잎벌레
Palaemon elegans - rockpool prawn are really elegant
Cochranella pulverata Glass frog. Credit to Geoff Gallice
Diphylleia grayi Skeleton flower. Usually white, turns transparent when wet.
Credit to Midori Mountains
Amphipod (probably genus Atylus)
Moonglow anemone
I found these both earlier today. It was a great beach day for me!
I have planned to make a project showcasing transparent organisms recently! I think I looked it up but the only one that fit the description was for a few specific ocean taxa that people get mixed up. I like fun little collection projects about interesting traits though. The problem is it’s addicting!
I can’t think of any of my own observations with transparency that are particularly interesting but this and traits like reflective organisms (not necessarily metallic ones) could be really fun.
Charidotella purpurata (Small Orange Tortoise Beetle)
Anisoptera (Dragonflies)
Annelida (Segmented Worms)
Caecidotea (American Waterslaters)(?)
Hadziida amphipods
Ischyrus pleasing fungus beetle larvae
My favorite is this the larva of this aphid eater, Eupeodes pomus.
To me, transparency in living things is always pretty stunning.
(my observarion here:https://inaturalist.ca/observations/179921366
As mentioned earlier, there is a project for specific transparent/translucent marine organisms: https://www.inaturalist.org/projects/jellyfish-comb-jellies-salps-and-other-transparents-transluscents Some of inclusions into that project that I have are:

Transparent is as transparent does!
I had no idea what this organism was until a helpful identifier came by and identified it as a hoverfly larvae:
Family Syrphidae | Hover Flies · 꽃등에과
This mayfly has its color coming in but you can kind of see the rear hind leg through the abdomen if you squint hard enough:
Stenonema femoratum | Dark Cahill