Aquatoid
The Aquatoid is a genetically engineered, ancient alien race closely related to their space/land based cousins, the Sectoid race. Some experts have disputed that the Sectoid race actually descended from the Aquatoids, judging by the webbing on their feet and hands.
Aquatoids possess average weapon skills and are extremely vulnerable to all weapons, including the rudimentary harpoon family. However, higher ranked Aquatoids are feared for their Molecular Control ability.
Live Specimen
The Aquatoid race is an ancient society, having existed millennia before man's first faltering steps upon the world. Their compact form and bulbous features are a throwback to their space faring brethren, the Sectoids.
Their power is based on the powerful Molecular Control technology. The Aquatoid race seeks to propagate its sterile race by genetic modification, the ideal subjects being Human beings. Experiments have spawned numerous hybrid races.
Autopsy
The detailed analysis on this creature allow us to make some basic assumptions. It is a Sectoid, our former foes, but changed by surgical methods and implants to be aquatic creature.
Vestigial lungs allow the breathing of air and limited surface mobility. There are cybernetic implants throughout the body, enhancing the strength of its atrophied limbs and the function of its organs.
As all members of this race are identical, we may hypothesise that these creatures are clones.