Remember the small Sunflower Star (Pycnopodia helianthoides) with eight arms? (Review the post from 17 December.) I mentioned that Sunflower Stars start out with 5 arms, add a 6th, and then continue adding arms in pairs adjacent to the newest arms until they end up with 20 arms (or more).
Today I found my first 10-armed Sunflower Star. It was very small, only ~2 cm across, but offered a chance to see the addition of the next two arms.
In the picture above, arm 6 is at 1 o'clock, arms 7 and 8 are at 12 and 3 o'clock, and arms 9 and 10, the newest additions, are the smallest arms just outside of 7 and 8. What fun to see this process in action!
Here's wishing for many exciting natural history observations for everyone in 2014!