No, there's 19 slots.
I don't count the weapon, shield, and mark as permanents. I count them as weapons, shields, and marks . IMHO, there's 16.
What about that icon there on the right?
I don't care what it "technically" is . It acts completely different from a permanent: You can only have one, it attacks last, and it can be flown. Shields have some effect on your opponent's creatures when they attack and you can only have one. Marks are always there and are indestructible.
Basically, there's a tree that goes like this:
Permanent
/ | \
/ mark \
permanents equipment
^ / \
| weapon shield
what I was counting
But does it really matter?
Nothing we talk about on this forum "matters". But I'm saying that all the cards in Elements are either creatures, spells or permanents. So if the question is: "Are weapons and shields permanents?", the answer is "Yes they are". They belong to a sub-category of permanents but that doesn't make them non-permanents.
Now you might find it more logical to give them their own main category, but that's just your own personal view (shared by many I'm sure). I could call Otyugh by "Mr. Hungry" because it makes more sense to me, but that doesn't change the fact that it's really an Otyugh. It's better to use the terms and definitions made by the game developer.
Original poster had a question, and Delreich gave the correct answer to it. I would say that this thread is resolved.