Nope no need for any specific shape, the main reason is it needs to be in clear air so as not to be effected by airflow over the fuselage, wing etc etc.... the PA 28 one incidentally is a straight blade with a drilling in the leading edge.......
what it will have in it is a small extra hole somewhere to allow air out....... this is because a pitot probe will also be effected by static air pressure, the bleed is to alleviate this so the probe just shows true pitot pressure without the static pressure effecting the reading.
Going back to the PA28 it is a double unit have the static port integeral in it too if memory serves me correctly.