Evolution of coral people

Let’s say that one day humanity discovers another species that resides in the genus Homo. However, unlike the rest of the inhabitants of the Homo genus, these species live completely underwater and have a symbiotic relationship with coral.

Appropriately named coral people, they reside in an area that is blooming with various types of coral, even ones that were previously unknown and undiscovered by science.

Appearance

The coral people are strikingly similar to modern day humans in physical structure, however, some notable differences in the coral people include a much more thin body structure, gills that reside on the side of their abdomen instead Of their necks, 2 extra opal like eyes that reside under their primary eyes, and the development of thin yet thick head crest.

Biology

The eyes of the coral people are both pitch Black in color and are shaped as opals, with the secondary eyes being noticeably smaller than the primary eyes. The primary eyes are able to see in infrared while the more smaller secondary eyes are capable of seeing both the visible light spectrum and in radio waves. Their head crest seems to be their primary mode of communication, using sharp thrumming, chirping, and humming noises, which sounds like a mix between a whale and a common bird. The skin of the coral people is spongy in texture, yet is as tough as chitin and is randomly covered In patches of coral of different species. The height of the species varies, with the youngest usually being around 5-8 feet tall and the oldest being around 25, Rarely however, some are capable of growing to 100 if not 200 feet in length, these individuals reside in the deeper parts of the ocean, and there mass is kept up by an extremely Tough muscular system, and a bone mutation that allows for their bones to become 5x more stronger and resilient. The coral people share a highly symbiotic relationship with the coral itself, with the coral providing an extra layer of armor and a direct source of nutrition, while the coral people Find places for the coral to grow and thrive, thus bringing a diverse array of fish species and nutrients.

culture

The culture of the coral people ties heavily on coral itself, preferring to live in coral filled caves. The coral people live in an area that is absolutely Covered in coral, with an majority of it glowing which if seen from above would seem like something out of an alien world, it’s also recorded that this area spans as wide as Hawaii . They seem to go off a class system as well, primarily composed of ambassadors, cardinal, bishop, with the rest being either farmers, or tool makers, but despite this they still treat each member of their species with equal amount of respect. The people are capable of crafting tools completely made of Stone and are capable of smelting metals near hydrothermal vents, albeit it is a very difficult and time consuming process. Lastly, they seem to have a written language that seems to be a combination between ancient English and Spanish.

intelligence

The species are seen to be pretty smart, having the intelligence to be able to build stone tools, use Very Primitive Smelting techniques, capture and even slightly domesticate local fish species, and even farms coral. They’ve been seen to be able to slightly communicate with humans, but this is still limited and is seen as a non effective way of communication.

This brings me to my question

how could these creatures realistically evolve?