A spear, depending on its type, can be used to slash or pierce. So the equivalent pole arm to go with, would be a Pike or a Glaive. Both do 1d10 damage and have the "reach" property.
Being polearms, though, they can't be thrown...
I'm pretty sure it is wrong. It shoul be something like 8lbs instead of 18lbs. It should weight similar to the Halberd (6lb) and the Glaive (6lb), which are its different flavour counter parts. Both with the same 1d10 damage + reach.
There is a certain logic for the weapons:
Longsword...