Question

What are cleithrum, supracleithrum and postcleithrum ?​

Answer 1

Answer:

The cleithrum is a membrane bone which first appears as part of the skeleton in primitive bony fish, where it runs vertically along the scapula.[1] I = "key (lock)", by analogy with "clavicle" from Latin clavicula = "little key".

In modern fishes, the cleithrum is a large bone that extends upwards from the base of the pectoral fin and anchors to the cranium above the gills, forming the posterior edge of the gill chamber.[2] The bone has scientific use as a means to determine the age of fishes.