So your work overall shows a great deal of promise and existing skill, but also shows that you've made a significant break from the principles covered in previous lessons, specifically in regards to your actual linework. In terms of your spatial reasoning skills, you've shown considerable improvement over your last lesson, but overall it becomes considerably more difficult to parse the specifics when your linework consists largely of broken and dashed lines.

It's very clear that your focus here was primarily on ending up with a pretty drawing at the end, rather than following the methodologies set out by the course and shown in the many demonstrations in this lesson. As you can see in each of these, I approach each and every mark in these drawings with confidence - each form is fully enclosed in order to encourage the illusion of solidity, and when I approach construction I am not at all concerned with how those marks will impede my ability to add detail afterwards. This is for a very simple reason: every single drawing in this course is an exercise. The focus is not on the end result, but rather on the process we employ. We are not learning to draw pretty things, we are learning how to convey forms such that they feel solid and three dimensional and solid.

You are clearly capable of this, but you need to be willing and able to follow the instructions exactly as they're written, not to modify the requirements to better suit a secondary goal you may have for yourself. So to that point, you are going to be drawing a few more of these so I can assess them as the exercise they're intended to be, and give you a more meaningful critique.

Now, to your question about aquatic animals - or more specifically, plenty of animals that don't necessarily follow this specific recipe, it comes around again to the lessons being about learning how to understand the spatial relationships between forms, and to be able to manipulate and combine them in various ways to create more complex objects. The specific recipe given with a head/chest/pelvis isn't going to suit every kind of creature, but working through them as exercises does ultimately help train our capacity to move beyond constructional drawing itself to understand how everything is three dimensional and how these forms fit together. In some of the newer content covered in Lesson 0 - specifically the three first videos (here's the first one) - I actually have a drawing in the background while I talk that shows absolutely no construction whatsoever, but does demonstrate an understanding of how everything I'm drawing exists in 3D space, rather than on a flat canvas.

There will be plenty of things you will want to draw that don't fit a particular mould, but they will all share this same basic foundation - that they exist in 3D space, not on a flat page. I think you've made considerable progress to grasping this on the intuitive level it is intended to, and that is exactly why you ended up going astray when tackling this lesson. Something appears to have clicked, and the drawings you produced ended up being quite nice, all this considered. You are indeed showing an understanding of the things you draw as existing in 3D space.

To that point, when looking at a jellyfish or an octopus, focus on the major forms you see. Some forms - like the bulb of a jellyfish - will have a particular focus on appearing more solid, so you focus on establishing that solidity. The tendrills in the otherhand will have more flow and fluidity to them. They're gestural to the extreme - where an insect or animal's legs, or even the stem of a plant uses certain techniques (branches, sausages) to capture its solidity and its fluidity, here the solidity is no longer much of a concern. With an octopus on the other hand, I would actually create more of a chain of boxes to capture the major planes of a tentacle structure - think something like this advanced version of the box challenge exercise.

Anyway, as I said, I'm going to be assigning a few additional pages below for you to demonstrate that you can apply the principles of drawing your lines confidently, enclosing solid forms without broken lines, and overall focus on these drawings as exercises rather than striving to do what you can to make the drawings come out prettily in the end.