The Nemean Bio-Form is a semi-sentient xeno that originates on the planet Echidna. The xeno goes through multiple stages in it's life span. The first is a worm like form, that poses little threat and often stows away on ships. The second is a aerial form, known as the moth, that can launch acid to attack foes.
The most well known form is named the Lion form, with leads to many knowing the creature simply as a Nemean Lion. In this form, the xeno's skin is totally impervious, and it is nearly impossible to kill. This has lead to the Nemean becoming infamous in many circles, including the Inquisition and Chaos.
When a Nemean dies in any older form, it generates a Larvae. A Moth form can generate at most two, while a Lion form can generate four or more. Opposed to the other two forms, the Larvae is not hostile, and flees from threats. It is about a metre in length, with wrinkly white skin. It moves with an undulating motion, and seeks decaying flesh to feast upon. It has strong jaws that can chew through ceramite.
When a Larvae form gathers enough bio-mass, it forms a hard cocoon around itself and begins to metamorphosis. When it is finished, it's skin has become tougher, with a light fuzz. Bat-like wings protrude from it's back, that have the a strength to lift itself into the air. It's inside has also changed, with it's stomach producing more acid then is necessary.
Although the Moth form can still move along the ground, it normally spends it's time flying. When prey is spotted, the Moth dive-bombs it, dropping acid that chews through most materials. Once the prey is incapacitated, the Moth lands and feeds with it's strong jaws.
Yet again, once the Moth has enough bio-mass, it metamorphosis. The Lion form is radically different from the last two; has the same body shape as Terran Lion, while being much, much larger. It's silver fur is completely impervious to harm; in fact, the only known way to kill a Lion is to shoot directly into it's mouth with a high explosive. A Lion Bio-form once survived a orbital bombardment from a Adeptus Astartes Battle Barge.
The offensive capabilities of the Nemean also increase. It's claws and teeth tear through Ceramite like paper, and it's speed is comparable to an Eldar Aspect Warrior. It's tail and can elongate and retract, and can be used as a manipulating limb or as a whip. The Lion form also has the unusual trait of being a pshyic blank; the warp or it's powers can not affect it.
Some research done by the Ordo Xenos suggest a 4th form is available to the Nemaen. Whispers of a great threat beneath the surface of Echidna, that demons fear to wake. Nothing has ever been confirmed, but the threat remains.