UML diagram diamond arrow

I do not have much experience with UML diagrams and was coming across a diagram which I didn't fully understood.

When I have the following UML diagram:

What my current understanding is about this UML diagram based on my research is that the observers are aggregated in the subject. And that concreteObserverA and concreteObserverB inherit from Observer.

Questions:

1. Is my current understanding which I described correct?
2. I saw in all sources from which I studies UML diagrams that they denote aggregation with an arrow. Is the relationship between Observer and subject still aggregation or is it something else?