What’s brainless, bloodless, spineless, heartless, and takes its stomach outside of its own body to eat food? You might be imagining an alien, but the answer is actually a starfish (Metazooa answer #470). Everything you think you know about starfish is wrong. First of all, they aren’t fish at all - they are related to sand dollars, sea urchins, and sea cucumbers, which are all echinoderms, a phylum of animal who have five-pointed radial symmetry. This means the animal can be divided into five equal sections.

Secondly, despite the walking, talking starfish we all know and love from his antics on Spongebob, a starfish actually has no brain at all. They instead have nerve nets, which is the simplest form of a nervous system found in multicellular organisms. It’s a distributed tangle of neurons, with each arm having their own nerve net, all connecting to a central radial nerve ring. This is partly what allows for limb regeneration, although it can take a starfish up to a year to grow a new arm. Interestingly, though we call them arms, it would be more accurate to describe a starfish as a five-pointed head, without much of a body.  

The third and maybe craziest thing about starfish is that they have no hearts or blood system. Instead, they use filtered sea water to pump nutrients through their nervous system. The water delivers key nutrients to the starfish, allowing for proper organ function. Using sea water saves space, as there is no need for a complex blood system, and sea water is highly abundant in the ocean. This also explains why starfish are only found in saltwater - they would not survive a freshwater environment. For animals with no brains, they can be quite clever!

Monday, November 11 to Sunday, November 17.

The following are the shortest paths from last week:

Play Forgeous for Nov 18