I remember an article several years ago about the collection of melo pearls owned by the royal familys of Vietnam. They were especially treasured there, unfortunately I do not remember the entire article but do remember it gave some interesting beliefs and history on them. I belonged to the Houston shell club at the time so it was probably in a presentation or in a chonchology magazine. The melo grows to large size but it takes years to do so and being a large animal and inhabiting shallow water it is vunerable to over fishing and unfortunately I doubt that the pearls are taken without killing the animal. They are sometimes referred to as bailer shells because their shape and size made them ideal for bailing water from canoes. The shells are used in jewelry and to make wealth items in many oceanic societys as well.
I haven't seen abalone pearls from the family Haliotidae mentioned. There are a wide range of types around the world so there should be quite a few variations. The largest known is a pearl from the red abalone found in northern California the largest shell I have seen was 18 inches at its widest measurement. I found pictures and information as the pearl is in the guiness world records but could not copy them to add here. The pearl is 4 inches long and 2.25 in. wide and almost 300 carats. The rainbow of colors produced by the abalone should be unique among all pearls and is very rare.
The other pearl not mentioned comes in purple, lavender or pink. It comes from the fresh water muscle Cyrtonaias Tampicoensis and is found mostly in rivers in northern Texas especially around San Angelo. It is often called Concho river pearl and was worn as jewelry and used in trade by native Americans before European contact. The Spanish explorers looking for gold in 1650 along the concho ( Shell) river they discovered the pearls and harvested them for a while but could not find enough fast enough so went back to looking for gold.
There is an industry around San Angelo harvesting and marketing the shells and pearls and a state licence is required. The people who began the more recent interest in these were Bart Mann and Jack Morgan who made jewelry and opened a store featuring these pearls. The largest example was perfectly round and a uniform pink 13mm. in diameter. My favorite jewelry they made were small pearls mounted in gold forming an ear of corn.