For centuries, naturalists have puzzled over what might constitute the head of a sea star, commonly called a "starfish." When looking at a worm, or a fish, it's clear which end is the head and which is the tail. But with their five identical arms—any of which can take the lead in propelling sea stars across the seabed—it's been anybody's guess how to determine the front end of the organism from the back. This unusual body plan has led many to conclude that sea stars perhaps don't have a head at all.
That’s pretty interesting. Using generic sequencing compared to other organisms, they’re missing the sequences for torso and tail. Plus the sequences that are usually in front tub down the center of each arm.
So is it one creature or a group of creatures?
One creature, they were just looking at where the genes expressed. There’s a surprising amount of commonality in the DNA between animals, so they’re able to look at where those common genes express on one vs another.
One creature that is all head.
Depends on how many chunks you slice them into…?