What stage of mussels feels like sandpaper and can live up to 30 days out of water?

The correct answer is Settlers, referring specifically to the juvenile stage of mussels, also known as "juvenile mussels" that come after the veliger stage. At this stage, they have hard shells that can feel rough or similar to sandpaper. Most importantly, they have developed enough resilience to survive for up to 30 days out of water, allowing them to disperse to new locations and establish themselves. This adaptation is crucial for their survival, as it provides them the opportunity to find suitable habitats even when water levels fluctuate.

In contrast, the veliger stage is the larval form of mussels that are free-floating and primarily rely on water for survival, making them unable to withstand periods outside of water. Adult mussels, while they do have rough shells, do not have the same adaptability to short periods out of water as the settler stage. Pearls do not represent a developmental stage of mussels but rather the result of a biological process in certain species. Understanding these distinctions helps to clarify the life cycle and survival strategies of mussels in relation to their aquatic environments.