Calpha Sea Monster

Calpha Sea Monsters are a group of particularly notable species on the water planet Calpha. They are known for being intelligent and for having superlative qualities, such as extremely potent venom, nearly impenetrable skin, or gigantic size. The name "Calpha Sea Monster" was coined by an early space explorer with little imagination (and who had clearly not encountered any of Calpha's other large aquatic species), but the name stuck and is in its own way merited by their prevalence in Calphian society and food chain.

Description
There are three species associated with the name Calpha Sea Monster. The Common CSM and the King CSM are genetically related, and the Tyrant CSM is only known to exist from anecdotal evidence and is not known to be specifically related to the other species, though physical descriptions are consistent with some close relation. All three species have serpent-like bodies with two forearms.

Common Calpha Sea Monster
Usually referred to simply by the unmodified "Calpha Sea Monster," these are easily the most populous and recognizable CSM, and perhaps the most recognizable of any species on Calpha. They are generally tan with green underbellies, and have a powerful tail that makes them faster than most of their prey. They boast prominent fangs with one of the more potent venoms known to science, and a rough skin that resembles a natural kevlar.

King Calpha Sea Monster
The King CSM is substantially larger than their common cousins, reaching up to 150 meters in length. They are easily recognized by their spiny frill surrounding the back of their heads. Their fangs are further back in their mouths and hardly larger than the rest of their teeth, and their venom is substantially weaker than that of the common CSM. Since King CSM stomachs are larger and capable of digesting virtually anything, they have been known to eat even armored vehicles. Their metabolism also diverts any strong metals to the claws on their hands, further aiding in their attack of artificial objects.

Tyrant Calpha Sea Monster
Long thought legendary and still only known from a handful of sightings, little is certain about the Tyrant CSM. Many believe there is only one specimen alive. No one has ever seen more than its upper body, but its length is speculated to be anywhere from 300 meters to 1000 meters. It is capable of creating a strong current into its mouth, supposedly much more than it could inhale into any internal cavity, so it supposedly has some way of continuously propelling water into and out of its mouth. It lives very deep in the ocean, well below the penetration of any sonar, and seems to only ascend when it senses something big enough to be worth eating.