it is not a snail it is a parasitic bivalve. they feed off of the circulatory system of the
starfish. it is extremely difficult to remove them without killing the Linkia. it is best to just leave the bivalve there. Linkias are very difficult to keep because they are extremely sensitive to changes in salinity. changes in salinity even weeks before you purchase a Linkia can cause disruptions in their circulatory system and can lead the Linkia "falling apart" and dieing. most of the Linkias you will buy will have one of these bivalves attached, they are pretty common and do not seem to cause harm to the
starfish unless there are a significant number of the bivalves.
if the starfish stays alive for over 6 months, then you could try removing the bivalve it you really want to, but i would just leave it. if the starfish dies in the next month do not blame the death on the bivalve. if the starfish seems to fall apart, even at the area where the bivalve is located, it is not the bivalves fault. a change in salinity caused the Linkias death. it might not be your salinity, it could have easily been the place your bought the Linkia from that caused it. it could even be the distributor that caused the death. when buying Linkias i make sure that the salinity of the water i am getting the Linkia out of is 1.026 if it is anything different, then i will not buy it, and you should not also. this means that the Linkia has been exposed to a salinity change and if not done properly its circulator system is damaged and will probably not survive. if you are thinking of getting a Linkia, make sure to bring YOUR refractometer to the store to check the salinity of the system you are getting the Linkia out of.
G~
