Mers

Name: Merpeople or Mers
Deity: Cyres
Lifespan: 100-120 years
Procreation: Sexual reproduction
Organization: Some do exist in familial pods or in groups, some are more solitary.
Language: Yes, multiple. Those of the deep sea have a low intonation like whales, while those of the shallows communicate a lot with fin and gil movements.
Appearance: Varies.
Mers from coral reefs tend to be brightly colored, while mers from shallow waters tend to have shorter fins. Those that are from the bottom of the ocean tend to be larger, while open water mers tend to have longer fins. River mers might have a more fish-like appearance, while some are shaped more like eels.
They frequently have sea-shell shaped ears, and baby Mers do not have a sex until they are past five years old and make their first shift to have legs. Those that never shift remain without sex until they do.
Strengths:

• Can breathe underwater
• Can shapeshift to walk on land
• Depending on the region they are from, they might be more susceptible to heat/cold, and nocturnal/diurnal
• Hypnotic song

Weaknesses:

• Long periods out of the water are harmful to them. (Harm dependent upon length of time out of water and writer.)
• Sensitive to dry climates, and climates that are outside their personal norm.

History: They are widely considered a myth originating with fisherfolk and sailors. Some are benevolent, where a mermaid led them out of a horrible storm; and some are malevolent, where they tried (or succeeded) in luring someone to their death.
Notable Mers of history:
The Queen's line - though rule is not passed down bloodlines in the combined country, those descendents from the following two women are colloquially known as the Queen's line.

• Ris Weaver - Queen Ris A'Dea (3422-3434) - The Queen of Terra Dei for the reunion of Terra Dei and Marē. Consort of Arburin Andorian and Nissa Felis. After her second term as Queen, she returned to the Weaver coast to live out her life partially on land and partially at sea. Neice of Queen Sikys of Marē.
• Sikys - Queen of Marē during the reunion of Marē and Terra Dei. Consort to Quin, and maternal aunt to Ris Weaver.
• The current Queen of Kardea is also descended from this line. 

Societal norms/mores: Merpeople in the underwater domains are as likely to have a king as a queen and have little perference for either.