Who are the proper subjects of moral consideration?

Morality is frozen ethics. Actual (dynamic) ethics is best considered as something situational and between interactants, an aspect of relationships.

Who then are the proper interactants?

The word "proper" implies an absolutist or religious stance, which may have no logical foundation in daily human inter-relationships.

"Morality" is a concept only attributable to humans whose distinct ability to contemplate "consequences of their actions" gives them them the psychological problem of the integrity of "self". Many philosophers think that "self" is a socially acquired ephemeral concept, so it follows that "self" acquires the norms of its social conditioning but is subject to contextual compromise. Hence for example the "thou shall not kill" rule is suspended in the context of "duty to ones country in time of war". Consider too the norm in some societies for "holy war" or "ritual slaughter of animals". The "selves" in such culture have none of the integrity problems of outsiders.

And with reference to Maslow's hierarchy of needs, "moral considerations" may simply be an intellectual pursuit for those with the luxury of time on their hands as a result of the material wealth they control.

Do no harm.

That still begs the OP question of "to whom or what".
Should we refuse to eliminate disease carrying insects ?....should we sacrifice one Siamese twin in order to sustain the other ?...etc. Essentially, questions of "morality" focus on such dilemmas.

Morality depends on society.

You seem to be suggesting that there is some universal morality that should fit any society. In reality, each society makes up its own moral system which includes the subjects that are of interest to it.

Each society makes it up for themselves.

Which is to say, morality is subjective.

Seems to me an argument can be made for a "moral" obligation to tend to our planet.

The movie The Day The Earth Stood Still made a point that may or may not be valid. The point was that there are a limited number of planets capable of sustaining life (as we know it)...and because of that, every planet capable of doing so MUST be protected.

That seems to infer a moral obligation.

Nonsense . . . what forms of life? Are we to sacrifice the environment for anaerobic life forms because we require oxygen?

Morality is is subjective.

You are making an unsupported assumption that life has value. (Maybe you only think that because you happen to be alive).

I'd be willing to take your position in a debate, although my heart would not be in it.

I acknowledge that I AM making a value judgement that life has value; I acknowledge that it is an "unsupported" judgement; and lastly I acknowledge that I have absolutely no interest in mounting a support of it.

I was, after all, talking about the point being made in a science-fiction movie about an inferred moral obligation.

Everything and everybody. It still remains that what it's meant is subjective to the individual.

Moral consideration only extends to those who belong to the class of beings capable of moral consideration.

The only thing missing from that proclamation was the roll of thunder as proof positive that it came from on-high and is infallibly correct.

I didn't mean to imply a religious stance by using the word "proper". I mean to ask who should we extend moral consideration to.
If you have qualms about an absolutist stance, would you be willing to answer "How do you and only you do decide who to give moral consideration and why?"
The comment regarding morality posing a psychological challenge to self is very interesting. Do you think that our ability to contemplate "consequences of of their actions" that you say is responsible for this conflict predisposes people to a utilitarian ethic?

I think that I made a poor word choice in my original post by using "moral considerations". What I mean is not how should we contemplate morality, but how should we practice it. What I was attempting to ask is more along the lines of "Who should we behave morally toward?".
Who's interests should we consider when we make ethical decisions?

Are infants or severely emotionally and/or intellectually undeveloped adults in this class?

Is every respondent so far of the opinion that there are no universal ethics?
How is moral relativism any different than moral nihilism?
Isn't this just a heart the claim that what is right is merely what is expedient for whatever culture is being used as context?

I understand that this is how ethics is practiced "in reality". A description of a moral system is not a justification for it.
Should ethical philosophy simply resign itself to cataloging the legions of competing moral systems of each culture and society?

Yes.