Chimeraes
Overview
Chimeras are a little-known species of merfolk, far more basal than either iarans or nix. They moved to deep sea in early evolutionary time, and as such have little to no connection to shallower merfolk or tellurans. As a result of this, they appear much less 'human' than other merfolk, and remain only myth.
Physiology
Chimeraes are most like iarans in physical appearance, that is, possessing of skin rather than scales, a cartilagenous skeleton, and lacking in the elaborate fins of nix. Unlike iarans, their fins are rayed, and they cannot sing or speak. The air sacs that allow iarans to do so have long since been reduced to vestigal membrane-bound pockets. These 'bubbles' are no longer filled with air but instead with luminescent bacteria- they function as a sort of breeding ground for this symbiote which then is transferred throughout the body as needed.
The chimerae's bioluminescence is unique in that it is not confined to a single cavity. Instead, the symbiote is moved throughout the body via channels from the light organ to other, smaller pockets of the body, in which the bacteria then glows until it is moved elsewhere, or dies out, assuming it is not being continuously replaced. Such pockets exist in: the cephalic, dorsal, and caudal fins, the fingertips, and beneath the eyes. In this way the chimerae can control which parts, if any, of their body glows, using this tool for predation and communication.
Driven in part by this culture of bioluminescence, is the chimerea's translucent skin. They evolved this way as a result of the combination of deep water environments and the aforementioned bioluminescence- pigmentation is a luxury that is both expensive and unnecessary in the deep.
Language
Chimeraes use a visual language, same as other merfolk, and while it shares some similarities to Optimana or Sign, it is fundamentally different as a result of both the time and distance seperating the language's origins, and the use of light.
Chimeraen sign (though there is no true transcription or translation of the language's name into a spoken or written word) is a light-based sign language, utilizing handshape, movement, and illumination to convey meaning. There are actually two major 'dialects1': one used at distance, and one for close conversation.
Because of the vastness, darkness, and turbidity of their environment, it becomes very difficult to make out details at distance. Thus, when signing with someone who is far from you, you use a dialect of sign built just for that. This dialect makes more use of larger motions and more light signals, especially those across the body. It places less emphasis on handshape, which may be hard to discern, and more focus on an almost morse-code-like pattern of flashing lights used in conjunction with basic handshapes and motions. In contrast, close sign is more akin to Optimana, using complex handshapes and more intricate light displays, while focusing less on movement.