Glucosamine is very well known today as it is one of the primary ingredients of nearly all over-the-counter products for arthritis and other joint problems.  Glucosamine is an amino sugar that is found in the shells of  crustaceans such as crabs and lobsters.  The glucosamine found in pills and capsules is made from those shells.  
    While the use of glucosamine for joint problems is well accepted today, it is also used for other health problems.  In Europe, it is often used for "Chronic venous insufficiency" syndrome while includes spider veins, varicose veins, leg ulcers and leg pain.  Doctors say there is not sufficient evidence to recommend it for that purpose, but it isn't going to make it worse, so it's probably worth trying.  Bowel inflammations such as Crohn's disease are also treated sometimes with glucosamine, but again, the jury is out according to medical authorities.  Other illnesses  that are sometimes treated with glucosamine, but not approved by doctors include AIDS, cancers, fibromyalgia, glaucoma, kidney stones, migraine, psoriasis and glioblastoma (a type of brain tumor).  
    If you are allergic to shellfish, talk to your doctor before using glucosamine, otherwise, it is safe and probably worth trying along with other treatments you may be on for the listed health problems.

Here is one interesting crustacean.  The giant Japanese spider crab which can have a leg span of thirteen feet.