My take on pebbles! I love speculative biology but im bad at doing it myself haha
There's a bit more stuff that I didn't illustrate, so i'll talk about it here:
An Eridian's appearance is based on genetics, but environmental factors are also at play
The pebble's appearance and body composition depends on which area (volcanic, oceanic, etc...) the parents are from, and their diet
If one parent's diet consists on food with heavy metals, for example, their pebbles have more chances to have a strong carapace or certain colors
Beauty standard on Erid are based often on how well the body resonates and how strong one's carapace is. Crystal-based Eridians are really pretty but some can be also weak, depending on which crystal their body is mostly formed of. Volcanic Eridians are considered pretty ugly (porous and brittle). There's a lot of variety on rocks and crystal types of carapaces. Oceanic Eridians are rare and respected, as they must have incredibly tough carapaces to survive in Erid's boiling oceans (Adrian is an oceanic Eridian)
There's billions of Eridians and none look like another, it is incredibly rare for twins to be born, but possible.
On a more sour note, while in modern times it's more accepted, traditionally it's frowned upon for Eridians with different body compositions to have offspring together. They can mate and join mate clusters however they please, but when reproducing gets into the mix, the more conservative Eridians will frown at the idea of someone with desirable traits having kids with someone who has none.
Rocky and Adrian have suffered discrimination for this, as Adrian is considered a beautifully resonant and strong Eridian (by people who don't really know them), and Rocky is not. People have told Adrian that they could have prettier pebbles with another crystal-based Eridian, and those people have been lucky to escape Adrian stomping them to death in ire.
P.S. I will note this when I post their full designs, but Adrian and Rocky planned to have a full litter of pebbles before Rocky was called in for the petrova mission. Rocky believed he would come back soon enough to form a family with Adrian, Adrian was more pessimistic about it. At the End, because of time dilation (Adrian is now "older" than Rocky) and radiation (Rocky being exposed to it), when they met again they had to come to terms with the fact that it would be dangerous for them to try.
