When born, a Solstelek is little more than a grub-like creature with two arms and a digestive tract. As it grows, the arms gain bird-like fingers/feet, and the end of its body turns into a long, leg-like organ. The front of its body gains a skull with jaws, made up of canines and a large shearing tooth at the top, and a horny beak at the bottom. This is only when it has no supplies to grow with, though. The ideal method of growing up for a Solstelek is for its parents to chase down and bite a suitable animal, paralysing it with a strong, fast-acting venom. They will then put the baby on to the creature, letting it spin a cocoon for it to assimilate the victim.
The baby's only part of its brain, the brain stem, attaches to the creature's brain by searching for the area in the body with the most nerve signals. It will then begin to assimilate the body, growing into the flesh and turning it into a Solstelek. Other fresh body parts can be switched and added to the metamorphosing creature, such as adding an extra set of limbs, or a tail, or gills. The Solstelek will join them together. When the Solstelek is developed enough, it will break out of the cocoon. Chemicals added to the bloodstream stops it from panicing throughout the process, preventing harm from coming to the baby. The creature's brain is expanded by the baby, letting it become sapient. All memories are kept, as well as parts of the personality. The personality may be added to, but the base is kept. The main changes that take place with the brain are exchange, addition or removal of certain instincts, such as gender and species attraction. The creature's gender is lost, replacing it with the Solstelek's. Solsteleks with a body, either assimilated or grown, can wrap their body parts in a cocoon with a fresh body part for it to be assimilated in. Solstelek children take about 2 weeks to grow to full term.
Psychology and HistoryEdit
Solsteleks treat assimilation as a holy matter. They watch the assimilatee carefully, deciding whether or not it is a good candidate. Good candidates are healthy, strong individuals with an inquisitive or generous personality. If it comes to sapients that want to become a Solstelek, they will have to answer questions and be watched by the parents of the assimilating Solstelek. (Some want to become Solstelek, as they can change their body to whatever they want, and can start their life freshly.) Individuals that are diseased, or display strange behaviour, are not chosen.
Solstelek are often cautious or suspicious of new individuals, but are kind and generous to those who they know and who they don't hate. They will often discuss matters such as sport, logic, philosophy and if there are any ups and downs to the body that the other has. (This can lead to some strange and awkward conversations between species.) They live in small groups of around 7 adults, with no monagomous pairings inside the group. Interbreeding between groups is common, but inter-group affairs are monagomous. They are frequently pregnant, and have no qualms with eating their non-sapient children. They only eat their children after careful inspection and evaluation of how common assimilatees are, though. (Very good children aren't eaten, even if it doesn't suit the mother at the time. These children are most likely to have to grow their own body, and assimilate extras on later.)
Solsteleks used to live on their home planet, Jatorria, with a couple of FTL-speed ships. First Contact, though, was a Cybertooth invasion force, and the Solstelek were forced to leave as fast as they could. They didn't have as many resources as they needed for the journey, though, and cannablism of those that had starved was common. By the end of the journey, they had under 800 survivors out of the 1 billion that had once lived on their homeworld. They had to land on a colonised planet, belonging to the Astin and a small group of Tikhio, who were (luckily for the Solstelek) willing to help them recover from this event.
I'm not planning to expand on the home planet of these guys, so I decided it got invaded and everything of interest wiped out. Credit to the maker of the Flesh Thieves for part of the idea. This was originally based on a fictional type of colonial amoeba that assimilated the bones of its prey, though.