This is an instrument I created last year, made from a sea urchin shell. I applied thick internal lacquer to the shell as naturally, the sea urchin shell is very porous and not suitable for a wind instrument. After sealing the pores completely, I shaped the embouchure hole, and drill 4 finger holes in it following John Taylor's ocarina design.
With this scheme, the instrument, pitched in concert C, is capable of producing 1 fully chromatic octave. However, with the open, flute style embouchure hole (as opposed to the flageolet ocarina style embouchure hole), lipping technique can bring the low notes of this instrument all the way to G below the treble staff.
Sound sample is here: