You are a large creature.

Your walking speed is 10 feet. You can move across vertical surfaces and ceilings without needing to make ability checks, and you don’t fall while doing so.

You can read, write, and speak Common and Undercommon.

Cochleari mature slowly and are considered adults at around 40 years of age, when their shells fully harden. They can live for 250 to 400 years under normal conditions.

As a reaction when an attack beats your armor class but before damage is rolled, you can withdraw into your shell. While inside your shell, your speed becomes 0, you are prone, and you can’t take actions or reactions until you emerge from your shell. You can emerge from your shell as an action on your turn one round after using this feature. 

Your shell has hit points equal to your proficiency bonus x your Constitution modifier (minimum of 1). While inside your shell, you have resistance to all damage except psychic damage, and any damage you take is applied to your shell instead of you. Your shell uses your Armor Class and can be targeted by attacks and affected by area effects as normal. While your shell is intact, you cannot take the dahs action and you have disadvantages on Dexterity checks and saving throws. 

You can use this trait multiple times, but only while your shell has at least 1 hit point. If your shell is reduced to 0 hit points, you take the remaining damage and become vulnerable to every intense of damage until your next turn. After your shell is broken, you can’t use this trait again until you finish a long rest.

After combat, you choose to spend one of your Hit Dice to repair your shell. Roll the Hit Die and restore that many hit points to the shell. This does not restore your own hit points and you cannot use this trait during combat. 

You have a pair of eyestalks that extend up to 1 foot from your head and can move independently. You gain proficiency in the Perception skill. While your eyestalks are extended, you can see around corners or over obstacles without exposing the rest of your body, as long as there is sufficient space for them to extend.

Your snail-like body is sensitive to salt. While in contact with salt, you have disadvantage on attack rolls and ability checks. Additionally while out of your shell, any damage from a weapon or effect coated with salt is doubled against you. This trait only applies when outside of your shell and this vulnerability does not affect your shell.