Mermaid Anatomy - A scientific outlook
Contrary to popular belief, mermaids are not human or fish at all. They are mammals with the appearance of a human being above the pelvis and the appearance of dolphins or whales below. All mammals are warm-blooded and have hair, and all female mammals have mammary glands (breast and nipples for feeding young). Fish have a completely different anatomy. Mermaids do appear to have scales, but it is possible that this is in fact a pattern or camouflage that resemble scales. Some species of mermaid also have twin-tails and there are even some that are completely humanoid in appearance, apart from scale-like skin and dolphin-like biology (sonar, respiratory, circulatory and skeletal systems). The mermaid is also known to have both a caucasian or negro complexion and some sighted have a greenish appearance.
Mermaids have organs in their chest that can operate as a lung or a gill, depending on whether they are in or out of the water. The organ expands and contracts exactly like a lung, yet has the ability to extract oxygen from the water. This allows the mermaid to 'breathe' water in the same way that they breathe air - by filling and evacuating the chest cavity. This organ is also needed to operate the larynx. The human larynx cannot operate under the water as it cannot be made to vibrate from water pressure, yet the mermaids larynx operates equally well using water or air. The mermaid circulatory system is also designed to withstand differing water pressures like that of the dolphin and whale, while the skeleton is light and pliable like those of a bird or dolphin. The lenses of mermaid eyes are also different and are able to correctly focus for use both above and under water. A mermaid is also able to hear on a different level to humans and has the ability to use sonar for communication and hunting purposes underwater.
In mermaids, reproduction is much like that of dolphins. The reproductive organs of both the male and female are akin to the dolphin and whale, and mermaid babies are born live (as opposed to hatched from eggs).
Females have human internal reproduction organs; however the vagina is slightly shorter, and the common urogenital opening (the urethra merges with the vaginal canal near the opening) is at the front. The opening can stretch as much as a human vaginal opening; mermaid babies are born live. A clitoris (which is the same color as the tail) is slightly below the urogenital opening, and an anus is above the urogenital opening. Mermaid vaginas are slightly smaller than human ones (since merman penises are smaller, explained below), so they tend to be more sexually satisfying to human males.
Males do have a penis, but it is almost as small as a human female clitoris and is the same color as the tail; it is hardly visible (this is the only plausible explanation to why no one has ever seen a penis on any of merman). It is used for urination, as well as sexual intercourse. The testicles are inside the tail, as opposed to the pelvis, since they require a slightly lower temperature to function properly (the human and pelvis part is warm-blooded, but the tail is cold-blooded). The anus is above the penis.
The mermaid mostly eats fish, but has been known to subsist on other meats, fruits and vegetables. There are some species of mermaid that are vegitarians only.
The mermaid is able to exist equally on land and in the sea, although it can become dehydrated if on land for extended periods of time. Most mermaids live in schools or pods, but some are known to travel as hermits. They can live in caverns below the sea and in undersea cities. The merpeople cities is more common on other planets, but in the future there will be build bigger merpeople cities on Earth. Some of the merpeople are more advanced technological and spiritual than Earth human and is several thousend years ahead. They have free energy, teleportation, interstellar space travelling etc. Some of the merpeople live on big space stations and on starships.