What's on my snail?

[74maddox]

Just bought some snails, any idea what's on this one's shell?

 

[ndrwater]

Another snail..

 

[AcroNem]

Yep. Another snail indeed

 

[74maddox]

Yep. Another snail indeed

Why does it look like a half shell of some type of clam?

 

[35ppt]

Redacted

 

[74maddox]

It's a Slipper Limpet, Crepidula sp.

Description
Internally, the shell is distinguished by a shelf-like, cup-like, or half-cup-like structure used for muscle attachment. Some calyptraeids have shells that externally resemble those of limpets, so species in the genus Crepidula are often called slipper limpets. However, these snails are not closely related to true limpets and are more closely related to conches and cowries. The "slipper" in the name "slipper limpet" is based on the appearance of the inside of the shell, which with its half-shelf resembles a traditional western bedroom slipper.

Reproduction
Calyptraeids may form a tower of up to 25 animals, sometimes referred to as a mating chain. The bottom snail is always female. When she dies, the male above her will change from male to female, and the chain continues.[3]

Calyptraeidae - Wikipedia

en.wikipedia.org

Thank you