Originally, the idea (or motivation) for this race, in terms of its characteristics, came from a short dream. This dream was admittedly fairly different from the current state of worldbuilding to which this race is associated: In the dream, I was a character set in world, in essence, with some sentient creatures with powers which could magically bond or ally themselves to people, somewhat like Pokemon in a sense except these creatures were not kept in balls and could come to speak my language as part of the bond.
At one point, I tried adapting this dream to one canon I had going, but after some progress, I decided to change the context to be more realistic and less fantastical on account of a decision to merge two canons, them being this fantastical/sci-fi one and another one of "harder" sci-fi. So on that decision, I dropped the stuff about bonding in the process and reassigned the roles of the races instead.
Anyways, I had the original depiction of this specific race to be more like gentle healers, with plant-like characteristics not too visually dissimilar from the Ralts/Kirlia/Gardevoir pokemon.
This resemblance can probably be seen in these initial sketches of the female variant below:


I didn't like the fact these sketches retained some of characteristics, particularly the head crest. So I tried to reduce it in later sketches, to which I developed the visual dimorphism with the male variant:

Immediately above are prototypes for the torso and other parts of extremities. I liked the sort of ribbons/stalks and fibrous appearance from the first sketches, as I think it succeeds in conveying a sort of delicate or elegant look, but I believed the whole thing needed to be simplified, as least when drawing out the naked form. One thought is that the ribbons could very well be potentially depicted as clothing instead. Anyways, I then used the female form as the base for the male form, after which I would have the male body to have some prickly features added to it. Not sure why I did it, but I think it could be excused as a sort of sexually attractive feature when/if I get to fleshing out the biological characteristics.

In the immediate above, I tried fleshing out the limbs and the heads for the variants. I ended up wanting some sort of tripodal feet and tripodal hands on long limbs while keeping some segments around the joints; it keeps the features looking plant-like and the feet & hands would look somewhat like roots. It can be seen I had some attempts at developing the male head before I ended up liking the one with the big dome. It can be seen that I accepted this female head, but I didn't particularly like the pointy crest for the unspoilered, new sketch because it still seemed like it was an easily derivative feature. To try to rectify this in the WIP sketch, one can see I tried some inspiration from the male head and added a small dome (or rather, a droplet) to dull the point.
One can also see that I experimented with another pair of arms. I thought that this could be a race with this feature, but I ended up ditching it, at least for these beings. I actually wanted a design for a race which actually had four arms or another sort of limbs, since the concept itself would fascinating for a large (perhaps human-sized) organism, but consideration of the placement of the limbs is an issue and I conjectured that many potential beings/xenoarchaids would likely not evolve to have more limbs than necessary due to the added energy that would probably be needed in actually using the limbs and so would be selected out for those with reduced extremities. The feature could be indicative of advancement and I might still revisit it, but I have another xenoarchaid race which I've sketched with more limbs which I may or may not consider posting at some point.
As a last bit, I will keep the orb/oval in the chest a mystery.