Yes, they do contain cholesterol. That is your question. But cholesterol isn't one thing, it's a combination of different fats. Without cholesterol you couldn't manufacture hormones, and nothing would move through your system. Cholesterol is only a problem when it sticks to blood vessels. That happens when cholesterol oxidizes. The worst form is triglycerides, which is found mostly in our dies in the form of hydrogenated vegetable oils. The second "bad" form is LDL, found in many different fats, for example, the fat in meat, in french fries, and in many oils. The other form most of us know about is HDL, the "good" fat, found in seafood, flax seeds, hemp seeds, algae. This is good fat, but Omega 3 oils aren't the only "good" fats. Some fats though to be bad aren't really because they have so many antioxidants in them. Don't worry about seafood, but do get an education on fats. There are many good books that will teach you about the different fats and how they can help or hurt, but most important is to eat a lot of foods high in antioxidants such as green leafy vegetables so fats don't "stick."
According to a study at the University of Washington, shellfish pose no danger to cholesterol levels. This study found that some of the most commonly eaten shellfish, including oysters, crabs, clams, shrimp and mussels, showed no evidence of raising cholesterol levels. Crab and clams actually lowered the LDL levels (bad cholesterol). Mussels and oysters also lowered LDL, while raising HDLs. Fish and seafood contain a small amount of cholesterol, but are also rich in healthy, unsaturated fat and low in saturated fat, the type of fat that tends to raise blood cholesterol..