Selkye toad

Selkye toads are a parasitic, unnamed humanoid species indigenous to the planet Selkye in the Zeta Stentor star system.

Background
These humanoids had similar skin texture and warts to toads and may have evolved from that branch of lifeforms. They had blue-colored skin, webbed hands with five fingers, and no tail.

They digested life energy collected by symbiotic beavos, small, furry, harmless-looking entities. Without energy to absorb, they hibernated in a dormant state, with their bodies desiccating into seemingly corpse-like husks. Though about seven feet tall when inanimate, they grew larger, stronger and more vibrant as they absorbed more energy, expanding to ten or eleven feet tall.

History
Long ago, Selkye toads killed all other animal life on the planet.

In 2266, the starship USS Enterprise (NCC-1701) brought an expedition of scientists and technicians to Selkye near an empty city of the long-dead Selkye natives. Professor Richard Spellman and his assistant Jean Ravel discovered several desiccated toad creatures in the city, along with a few affectionate beavos. Doctor Leonard McCoy kept one beavo as a pet, but by the next morning, he felt sick and exhausted, whereas a toad creature that had been brought aboard the Enterprise for examination became invigorated, broke out of storage in sickbay, and assaulted the crew. A phaser stun returned it to a dormant state. Nyota Uhura took over caring for McCoy's beavo, but many hours later she exhibited the same symptoms as McCoy, whereas the toad creature reanimated and went on a destructive rampage.

Meanwhile, on Selkye, expedition members barricaded themselves within their base camp, all extremely weak, as several large toad creatures attacked. Kirk locked all the beavos inside metal containers, and within a few hours the Selkye toads had collapsed and become dormant.