In addition to what OrionN pointed out, for me the evenly spaced tentacles are also an indicator. When the tentacle length points more towards gigantea instead of haddoni (though I have seen haddoni with long tentacles), I then look to see if the tentacles are in rows when the oral disc is exposed. Gigantea tentacles are arranged in rows, usually rows of two or three tentacles that radiate from the mouth outward. Helianthus tentacles are evening spaced throughout the oral disc.