Given a TV budget, why "crabs"?

[Tim Thomason]

It's kind of interesting that Roddenberry wanted to avoid humanoid aliens early on. If the Talosians had been crabs, it would've made the inability to piece together Vina properly make a little more sense.

Alot of measures in that first season were to avoid showing humanoid aliens. Spock was introduced as part (or half) alien, with a father that looked like Balok. Balok was a puppet later played by a small child. There were no aliens in over half of the first season, and several episodes (Charlie X, Squire, Shore Leave, Arena), feature aliens who probably take on the illusion of humanity. Balance of Terror had the Romulans look like Spock for story reasons (retconning the full Vulcan appearance), and then Miri had the human Onlies, but that was on some weird duplicate Earth. The Alternative Factor features some guy who I guess was supposed to be a human time traveller, but it isn't until Return of the Archons, 22 episodes in, that TOS introduced us to a species, w/ no explanation or uniqueness, that was near-identical to Humans (followed shortly by Taste of Armageddon and Errand of Mercy in the first season).

 

[Christopher]

It's kind of interesting that Roddenberry wanted to avoid humanoid aliens early on.

He didn't. It's clear enough from the original 1964 series prospectus that he intended most of the episodes to focus on Earthlike worlds with human-parallel cultures, since that was the only way he could make the show seem affordable to network executives. He no doubt hoped to do a mix of humanoid aliens and more exotic creatures -- which is, in fact, what we got, with creatures like the Salt Vampire, the Horta, the Gorn, the Melkot, the Tholians, the Excalbians, etc. As for "The Cage," he may have been thinking that a pilot is where you go big, to show the best of what you're able to do, before dialing it back to more modest stuff in later episodes. And he was probably influenced by the then-current The Outer Limits and its heavy use of monsters-of-the-week.

Alot of measures in that first season were to avoid showing humanoid aliens. Spock was introduced as part (or half) alien, with a father that looked like Balok.

Spock never said his father looked like Balok. He said "In some manner he was reminiscent of my father." He didn't specify a visual resemblance, and "in some manner" makes it clear that he was speaking of some non-obvious quality.

Balok was a puppet later played by a small child.

Err, children do count as humanoids.

There were no aliens in over half of the first season, and several episodes (Charlie X, Squire, Shore Leave, Arena), feature aliens who probably take on the illusion of humanity.

The Thasian explicitly said that he had taken on his form of centuries ago, so yes, they were humanoid. And there's absolutely nothing to suggest that the Caretaker or the Metrons were anything other than corporeal humanoids with advanced technology. Generations of fans have mistaken lens reflections from the Metron's shiny costume for some kind of energy effect, but the Metron gave no indication that he was anything but a boyish-looking, 1500-year-old humanoid. And TAS: "Once Upon a Planet" established that the Caretaker was mortal, having died between the two episodes.

The Alternative Factor features some guy who I guess was supposed to be a human time traveller

Lazarus clearly stated that he was a native of the planet featured in the episode, a time traveler from its distant past before its destruction, and therefore not an Earth human. He did call it "my Earth," but he meant it metaphorically, as in "the planet that is to me what Earth is to you." So, yes, he was a humanoid alien. He was called "human," but it wasn't uncommon in SF of the period to use the term "human" for aliens who looked identical to humans.

So there are a lot more humanoid aliens in TOS's first season than you acknowledge. I'd also add the extinct Exo III Old Ones, who presumably looked like Ruk.