ICMP doesn't use specific ports, although it does use types. Here's an interesting tidbit that explains this a bit - particularily with respect to firewalls.

http://www.robertgraham.com/pubs/firewall-seen.html#2

Outging, we use Echo requests (type 8). Incoming, we use Time exceeded in Transit (type 11), Destination Unreachable (Type 3), and Echo Reply (Type 0).