While the cartoon starfish Patrick Star from "SpongeBob Squarepants" is famously stupid, his real-life counterpart in science may in fact be all head. This at least is the conclusion of a landmark recent paper in the journal Nature, which solved a lingering puzzle about starfish anatomy by turning to the enigmatic echinoderm's genes. Echinoderms like starfish have a five-fold body plan but, mysteriously, still must have evolved from ancestors with two-fold body plans. The scientists analyzed starfish genes and compared them with genes from vertebrates like humans (which have two-fold body plans) and acorn worms (which also have two-fold body plans, but are closely related to echinoderms).
Their astonishing discovery? As it turns out, starfish do not switch on the genes that would give them a trunk with an abdomen and limbs. Instead, their body plan develops from the genes that acorn worms and vertebrates use to develop their heads.
"To summarise starfish anatomy, I would say it’s a mostly head-like animal with five projections, with a mouth that faces towards the ground and an anus on the opposite side that faces upwards," Dr Jeff Thompson, a co-author on the study at the University of Southampton, told The Guardian. In an accompanying opinion piece, Thurston Lacalli from the University of Victoria in British Columbia described the starfish as “a disembodied head walking about the sea floor on its lips — the lips having sprouted a fringe of tube feet, co-opted from their original function of sorting food particles, to do the walking.”
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