This dream is showing how you are gifted in certain areas in your life that not many are able to acknowledge. You most likely have the ability to lay hands and heal or other similar gifts. Being swallowed in the back of your mother's house can be showing certain thoughts or concepts that are trying to "swallow" you or take you away from your understanding and knowing you have these certain gifts. Since you went to hide the seashells, you may have a hard time sharing this with others.
Yes there would be a huge connection with the sea shells. With them being very old shells and being in your moms house, it is showing these gifts are passed down from your mother. She may or may not have been outspoken about her gifts. Some will usually hide their gifts as they are afraid of what others might think. In this case your mother may have been more quiet about her gifting. You are being given the dream so that you can flourish and grow in these gifts even more so then your mother. You are the next generation to make use of them. With each generation if the spiritual gifts are used outwardly, they will grow even stronger with each generation. If you have children or will have children these gifts will then be passed down to your them.