C

1) abbreviation for caudal fin

2) abbreviation for caudal fin rays

3) Carboniferous, a period within the Paleozoic Era ca. 365-290 million years ago

4) the Roman numeral 100

5) degrees centigrade, a measure of temperature. Note that 12°C is a temperature while 12C° is a number of degrees or a range, e.g. 20-31°C inclusive