This Pisaster brevispinus has a pretty dramatic split arm. I wonder how they control the regrowth of limbs to reach the same length as the others. This photo is from Neck Point in October 2010.
Seastars can drop their arms if they feel threatened, a process called autotomy (“self-sever”), and regrow the arm later on. But sometimes things go screwy and they don’t regrow quite right. Seeing six arms on a star that should have only 5 is fairly common. These photos are from one of the more unique examples I’ve encountered.
Can you see the little nub on the Pycnopodia helianthoides arm?
And yes, there are tube feet on the bottom, just like any proper seastar arm.
Pycnopodia helianthoides is my favorite example to use when students complain about having to learn the scientific names for organisms. As long as the describer didn’t name the organism after a person or a place, the scientific name can be very descriptive. “Dense-feet sun-flower-ish” is a very accurate description of this star.