Hum... I have to think some more about organs. Silk production.
A small tube that would produce silk. The creature would use it to make traps or hang in places. I think it is too complex and should be added latter, it would require a lot of physics.

Gular pouch: Can hold water and food like that of the pelican or can produce various noises like a frog.

Bone Plate: A hard bone plate that can be added outside or inside of the body. It gives the creature more defence. The outside version could evolve into a shell.

Acid Production: A small tube that produces acid. If added inside the creature, like in the blood, when a enemy bites you they take damage. If added in a gular pouch it gives the crature the hability to spit acid. Maybe add some color pallets to the acid would make a lot of people glad.

Spore holder: It lets certain flora "grow" in some parts of you body. It would be like hair folicules, the only exception would be the fact that it would require a seed or a spore to touch the area and after some time the plant or fungus would start a symbiotic relationship with you creature.

Tongue: Eating, but if muscles are added around it and you prolong the tongue it can be shot like a cameleon.

History Lesson.

We mentioned reproduction.
People got bent out of shape.
It got out of hand.
ADMIN crunched them like bugs.

/History Lesson.

Wanted to add that this thread is now open for detail part suggestions as well. I'll probably start off with osteoderms, quills, skin tags, the fun stuff, but we'll also have to put in a progression of different base skin types.

I'm glad you liked scio! I will have to think about some more organs.
Eel's muscle can produce some sort of energy ( Calli must know). Vermifoid use their mucles to dig. So what about different kinds of muscles that let's you make different things. I have only theses two exemples.

"Crystalizator": It would be a excrete system. (I don't know how it could work in real life) So let's say your creature eats something that produces a very toxic waste or can't excrete properly. So crystals can be made of impurities. So this organ would be like the spore holder but it would transform excretes and force that reaction with carbon or syllicate. The only exemple that can make something "like" that would be the clam and the pearls. I don't think it is possible but it would be pretty cool. Biology gratification needed.

Thermic Sac: So let's say your creature can't mantain it's temperature very well. So this organism lives in a vary cold place but there are some hot springs placed around the globe. Most of the life is based on theses hot springs. Some creatures can go to one hot zone to another, but if they go very far they die. With the Termic Sac the creature can hold the hot water or gas and place it in a sac with isothermic material. When it reaches a certain temperature it would liberate the water or gas into the bloodstream(water/liquid) or "mini"-lungs(gas). This Sac would let the creature walk/fly/crawl for more time in very cold temperatures.

Cascavel's Bell: It would scare some predadors or immobylize victims with fear. I think this is a muscle too.

Electrocytes are made up of modified muscle tissue. They should definitely be included. The hot water sac is just a bladder associated with a certain environment and behavior.

I had an idea, sort of. Not a new organ, but an addition to an existing one.
So, basically, it would be an addition to the stomach. It would concern the stomach acids.
It would be a set muscles that would work like a pump, letting the creature to pump out the stomach acids and spit them out of their mouth. It may not be a powerful attack, but, that would depend on the strenght of the stomach acids. But, before the stomach acids are strong enough, the creature could make their prey/predator blind by spitting the acids into their eyes. EYES.

That's all from me, pretty much.

Not a bad idea.

So cascavel is rattlesnake in english. I didn't knew that...
The termic sac would be usefull for reptiles and amphibians. Water for amphibians for hydratation reasons and gas for reptiles. Maybe the crature have to go to another hot spring for reproduce or walk on the desert (with cold water instead of hot)

I also got an idea that, if a creature ate a lot of quartz/flint/silica (you know, that stone that does sparkles), it could evolve their teeth being covered with it from birth/getting it a while after birth, which would make their teeth create sparkles.
The creature could also evolve some sort of a baldder that would either produce some sort of a flammable liquid or gas. They could then spit/breathe out the liquid/gas, therefore being able to sort-of breathe flame. Or, covering the enemy creature with the liquid and then grinding their teeth near the said enemy creature to set them a-flame.
This is sort of a conbination of science (flammable gasses/liquids) and fantasy (breathing fire, like a dragon). But, technically, it would be possible in the real world.