Merfolk

Also known as sirens.
Legends of alluring humanoids who live under the sea and who are part-fish or part-octopus are common in cultures around the world. In the Eastern tropical oceans South of Suneka and North of Nafena, these legends speak to a grim reality. Merfolk, creatures with a humanoid appearance who beckon sailors to join them in the water, are real. They just aren't friendly. When a sailor or beachgoer does make the mistake of swimming out to them, the merfolk violently assault and attempt to consume them. These are not sentient creatures, but ruthless pack hunters drawn to hunt humanoids in particular.
There are two types of merfolk/sirens: Most commonly known are your average mermaids. These fishlike creatures grow to look more humanoid in their upper half as they age, and are the more mobile and common of the two varieties. Mature specimens are about what you'd expect from a feral merfolk: upper half person, lower half fish, get close and they try to murder you. These are pack hunters and extremely social among themselves, and generally only fight one another for mating opportunities. These merfolk are (unknown to most people) the males of the species - they spawn in large numbers, and physically fuse with the much larger females to mate.
Rarer are the more intelligent and cunning "sirens" or "deepfolk", who lurk in the murkiest depths just barely in sight, and only come to the surface in deep fog or the depths of night. Deep sirens are actually enormous fish averaging 30-50 feet long, which dangle humanoid-like appendages to lure people in. These appendage-sirens can appear fully humanoid (outside of the fleshy tube connecting it to the main fish), and the fish can even mimic song or elements of speech to lure other creatures closer to it.
There is one ageless Siren, known as Moksetar, who is truly massive and has a pre-programmed protectiveness of other sirens. Moksetar is also non-sentient, but could arguably be classified as an immortal. Moksetar and the species as a whole were created by The Masked One

Basic Information

Genetics and Reproduction

When a mermaid is sufficiently old and is ready to die (anywhere from 10 to 70 years), it shifts priorities from feeding alone to mating. When a mermaid ready to mate encounters a siren, it will leave its existing group for the siren's entourage. After courting the siren (which may include food gifts, fights with other mermaids, and courting dances), the siren will release pheremones indicating its ability to mate. The mermaid will then shed its disguise and physically fuse with the main body of the siren. The vestigial mermaid will then slowly be absorbed into the siren, though its internal sex organs will continue to live and produce genetic material for the siren within her body. The knowledge gained via devouring is also passed to the siren in this process. 
Once the siren's eggs are fertilized, they are released and kept for safe keeping under the fins of the siren for several months. When they finally hatch, the infant sirens stay with their mother and are raised in a curiously mammalian fashion. The mermaids, meanwhile, form their own swarms and leave to join other merfolk at the first opportunity. The babies are cared for by the siren's mermaid entourage, but may be forced to leave early if the entourage is insufficiently large.

Growth Rate & Stages

Mermaids look like big old murder-fish with clawed semi-humanoid arms at birth. They slowly gain humanoid upper halves as they eat humanoid flesh - in a curious magical process, they seem to be able to gain knowledge of beauty standards and body language from the flesh of their prey, which they instinctually use to model their upper halves through adolescence. 
Sirens are basically just angler fish until they reach the age of twenty, when they get large enough to produce humanoid lures. Sirens do not need to eat flesh to gain knowledge of humanoids - they inherit the accumulated lore of their mothers. 
When a siren dies, their entourage carries their body to the nearest group, where they are cannibalized.

Additional Information

Geographic Origin and Distribution

Sirens are found in warm waters of the central-Eastern seas. Most are found in their place of origin: the Siren Seas North of Nafena, particularly surrounding their great nesting grounds surrounding the Palace of Halcyon. 
Some groups have spread across the oceans away from Nafena, towards Southeastern Suneka, Northern Maradia, and Eastern Ukaram.

Average Intelligence

Merfolk are not sentient, but do have an advanced predatory cunning - they are excellent readers of tone and body language, and have a mind for ambushes and chasing prey. Sirens are more intelligent, but are not sentient either: they can use tools and have object permanency, but they don't understand what the words they can parrot actually mean.

Lifespan

100 years

Average Length

Males 6'6"; Females 30'

Geographic Distribution

• Maradia
• Nafena
• Suneka (place)
• Ukaram