Arella's Physiology

Species name: Amphitritinae syreni



Aquatic hominid. They evolved from land caudal hominids before they were forced to adapt to an aquatic existence. The landed ancestors had already begun tool making, so they retained the use of their arms and hands. Over millions of years, their legs and feet atrophied away while their tails evolved into power dolphin like flukes. Their bodies have become streamlined for quick swimming ability.

They are homeothermic (warm blooded) air breathers. An array of gills cover their heads, but these gills can only extend their time underwater. They have opposable thumbs and their hands have four webbed digits with sharp claws.

Gender differences:

Males' penises the extend from within their bodies during arousal.

Females have two mostly flat breasts they use to nurse their young. Their mammary glands reside within their body to maximize its streamlining.


They do not have echo location capability. Their eyes are large and have a tapetum lucidum increasing their sensitivity 7 fold. Their visual acuity, however, is only 20/43.

Their eyes are evolving to be laterally facing. Each eye can move independently so they can see stereoscopically or see a much wider field of view than us. They can focus in both air and water.

They have a very weak sense of smell compared to humans. Their hearing range is 32-43,000 Hz with similar to human sensitivity.


They give live birth typically to a single child. Sexual maturity occurs around 12 years of age. Females are continually fertile between puberty and roughly 40 years of age. Females do not have menstruation cycles. They engage in sex for both reprodution and pleasure.


They are relatively healthy, but limited tool making due to their environment greatly limits their medical abilities. Their lifespan is around 65 Earth years.


They are strong swimmers and can hold their breath for a long time. Gils protruding from their scalp can gather some additional oxygen from water, but not enough to allow full time submersion. They are active both day and night. Each brain hemisphere is asleep for half the day.

Bio compatibility

They can metabolize Earth food. They are not effected by Earth viruses or most microbiotic pathogens. Their microbiotic pathogens do not harm Earth life. (Pathogens are usually too specialized to harm other biosphere organism's, but some planets have been found to be incompatible).

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Copyright 2017-2018 by David White

This page last updated 24-Jan-2018