Musical instruments that start with the letter I include the igil, ipu, Irish uillean, Irish bouzouki, ichigenkin, inci, iya, itotele and istarski mih. The instruments originate from countries ranging from Cuba and Ireland to Croatia, Japan and the Philippines.
Bessel's functions are often used in acoustics for describing circular membranes behaviour (exploited by most of the musical instruments). They are the solutions of the wave equations using polar coordinates. Set the properties of the membrane Bessel's functions describe the vibrational modes of the membrane.
Even the adults, though usually sessile, may move, when necessary. To do so, the foot is inserted into the ground and then pumped up with blood, so that it serves as an anchor, after which the mussel can pull body and shell over the ground. The same way mussels dig themselves in the ground (see picture above).