All [utensils made from] sea [creatures] are tahor except [utensils made from] a “sea-dog,” since it flees to dry land. These are the words of R’ Akiva. If one makes utensils from something that grows in the sea and attached to [the utensils] something that grows on land, even a thread or a string, something that is susceptible to tumah, [the utensil] is [susceptible to] tumah.