Races of the Source vs the First and those unique to each

[Enkidoh]

There is a sort of goblin on the First, hobgoblins specifically, although they don't seem to be a beastrace per se and just generic monsters fought on the beaches in Kholusia (also, like the Eorzean/Source goblins that take the appearence of FFXI's goblins, the First's hobgoblins actually take the form of FFI's goblin enemies instead). So whether the hobgoblins are a similar race to the Source's goblins (and just evolved differently) or are a completely different species is unclear (I'm liable to lean towards the later theory myself though).

I think too much of the 1st Shard has been destroyed to say if the races we don't see on the 1st Shard weren't actually there at some point in time. Other then races like the Ixal (which are Allagan creations) it's entirely possible they migrated to different parts of the 1st Shard and were simply swallowed up by the Flood.

Most of the fae races in Ill Mheg were specifically mentioned during the MSQ as having fled to there from elsewhere on the First due to the Flood (only the nu mou were native to the area, having been shown in Echo scenes to have been there during the heyday of the Voeburt kingdom at least), so in reverse it is highly likely a lot of 'missing' races from the Source that haven't yet been seen in the First were simply rendered extinct by the Flood.

We've already seen that Roegayden and Au Ra are in the location of Corethas (instead of Elezen), while the Kobald and Lalafel swapped places. There's also primarily Viera in the place the Black Shroud is instead of Elezen. And the Elezen were in the 1st Shard's verions of Mor Dhona. So there's already a precedent for different races settling in different locations on the 1st Shard compared to the Source.

A lot of that could be just put down to "it's a paralell world so things turned out differently there", but you also have to remember that most of the current day races in Eorzea on the Source have had constant cycles of migration and the rise and fall of successive nations due to the constant cycles of Astral and Umbral Eras, with Calamities serving as a repeating cultural reset button, none of which ever happened on the Shards, until the First was hit with the Flood of Light, and then everything there went to hell in a handbasket. So the races of the Source have long been moving around the world, settling nations that are often destroyed and replaced when a Calamity hits, something the First never had.