Diagramming messages on a service bus

Diagramming messages on a service bus

I'm looking for a way to clearly diagram how multiple applications
communicate via a service bus. The best I've come up with so far is a
sequence diagram, but I really don't like that. Sequence diagrams imply
some sort of sequence and that's really not what I want. Since every
service communicates with the service bus and sequence diagrams place each
service on a separate column, as the number of services increases, you end
up with a lot of overlapping arrows.
For example, given 4 services FOO, BAR, BAZ, and QUX:
Foo publishes messages of type publish and regen.
BAR publishes messages of type requeue.
BAZ subscribes messages of type publish, regen, and requeue, and publishes
messages of type transmit.
QUX subscribes messages of type transmit.
Any service can publish any message type at any time (there is no implied
sequence).
What kind of diagram should I use to can I clearly and unambiguously
represent this information?
Here's the best I've come up with so far: