I used so much colors because I had in mind traditional painting style and couldn't restrict myself to a limited palette. It's difficult for me because I like colors =) I'll try to make it over according to all advices.

(wth!? i just poted an huge ass comment, and then my "..session ended unexpected... as i wanted to post it" !!!!!! )

aaanyway here we go again..:

robin has some points there....

also i think, since u are a beginner u should go for a smaller canvas first, maybe 64x64 or less, to learn how pixels can work together and how the eye can be tricked by suggestion... pixel art is about placing every picel intentionally, on small scale it can make a huge difference wether a pixel is here or there.... also colors are very important, a pixel with this or that color can look like something completely different... u have 73 colors!! now, thats way too much since the overall feeling is more like dark blue, midblue, bright blue... the fetus has diffrent blues than the background, which is not even visible, so u could have easily picked the same colors for both...try choosing ur palettes thoughtful, .... another thing is, that when using a few colors only, its much easier to change stuff... i often think its good to start sketching with like 4 colors (dark, 2mids, light). that way u have a very high contrast and its easier to get the light and shadows right, further refinement, blending and coloring can be done later, but  its very important to have a good base 

heres an edit  ..., maybe it can give u some ideas.... note its only 5 colors.. 

Thanks for your suggestions, I'll work at it more carefully! 

This is a super nice idea.  Concept is nice as with shadings, but it could be cleaned up a whole lot.  Black lines are jagged, and you could use the dark purple to AA.  Another thing is that you should keep the colors low.  For the background, you can use less colors, but dither more to make it still look smooth without using as many colors.  Messy dithering is OK too.  And eye could be cleaned up too.  Top of the eye is missing hairline.  Larva thing is looking pretty good, but it doesnt stand out enough.  Adding an outline to it can help keep it from blending in with the background.

I cant find his other eye D:

Welcome!