It can be seen behind Newt Scamander in the attached image. Only the creature's eye is shown during the movie's runtime from 32:37 minutes. Its eye glows, it's in some sort of aquarium.
It is common within fictional worlds like the Potterverse to fill backgrounds with creatures that were never actually named in their source material. I do so believe that this creature, as interesting as it may be, is one such example of this trend as it's never directly addressed/stated. Even if it isn't officially named, though, that doesn't mean J.K. Rowling won't release a Fantastic Beasts Bestiary that includes these creatures with more detail, possibly written in Newt's handwriting and style. (There is a Bestiary on Pottermore, but it is in no way complete with all things Newt would have seen.)
If I were to guess based on the limited visual data, I'd suspect it was a Horned Serpent which is a large, dark serpentine creature with large, blue eyes. While you could argue that's more of a green than a blue, I'd argue it's more of a seafoam color, which could still be considered a form of blue-green. Otherwise, the creature is not yet named and is awaiting such treatment from Rowling.
Unclear - it may just be a visible habitat.
It’s unclear if that glowing thing is in fact a creature, or simply something that’s not a creature, but is actually instead a part of another creature’s habitat. Like his case, Newt’s basement has several different types of habitats for his creatures based on their natural environment. Portions of them are visible through their entryways.
Though it’s possible the glowing thing seen in that particular window is in fact a creature, it’s not necessarily one, and what exactly it is never was mentioned. It may be either a creature or just something that’s part of one of the habitats in Newt’s basement.