Malaysian Trumpet Snail
Malaysian Trumpet Snails are a very common aquatic snail. Luckily they are completely harmless. They do not eat plants and their burrowing helps to aerate the substrate and prevents dead/anaerobic spots. MTS are extremely hardly. They can live in hard or soft water and low or high pH. Additionally MTS have a trap door they are able to close to protect themselves in unfavorable conditions. I broke down a tank and put the substrate (Eco-Complete) outside in a bucket. There was only a small amount of water in the bucket. The bucket was outside on my patio for two months during the winter (Arizona winter so below freezing is rare) and when I used the substrate again some of the MTS had survived.
MTS will usually burrow in the substrate during the day and come out at night. Often times few if any MTS will be visible during the day and you won't know how many you truly have until they all come out at night.
When well fed, often the result of overfeeding your fish, MTS are extremely prolific. MTS have live young so they will not lay eggs around your tank.
Malaysian Trumpet Snails have a trumpet shaped shell that is a brownish color that typically gets darker as it reaches the point. I have seen several different morphs of MTS with some being a darker brown and others being a light brown with dark spots. When MTS are kept in softer acidic water the points of their shells will start to dissolve, starting at the point. Their shell is also extremely strong and can not be easily crushed by hand unless the shell has been damaged due to soft/acidic water.