Recently I purchased a video tutorial for a sea beastie by Fugazi1968 and although it is for Silo I own I try to follow the modelling parts in Blender.
I didn’t had much spare time but actually I’m at the 8th video and can show you the results of the last 7 videos:
Let’s start with circles:
Make a mesh out of all these circles:
I couldn’t find something like Silo’s “fill holes” so I had to fill every single face separately.
Joining fins:
Joining tail:
Closing caps: