Marine Biology Fact of the Week: Echinoderms, how cool are they? Part 1

One of my favorite phylums in the ocean are the Echinoderms. This phylum includes sea stars (starfish), brittle stars, urchins, sea cucumbers, sea lilies, and other variations of these animals that are ONLY found in the ocean. The most widely known and, in my observation, the most popular, are the starfish. You always find them in children's drawings of the sea, depicted with most, if not all, pictures of mermaids, and as characters in movies/TV shows (*cough* Finding Nemo *cough* Little Mermaid *cough* Spongebob Squarepants *cough cough*). But they're personally not my favorite. Urchins are my personal favorite. But I'll get into that later!

These guys all have some really cool characteristics. We'll start with some (not all!) that they ALL share and then get into their specifics. 

A sea urchin's test (or shell) can be split equally in all
directions when cut along the mouth axis
(or middle of the body)

The creatures classified within this phylum all have radial symmetry. This means that if you take, let's say a starfish, and cut it in any direction along the main axis, each section should be identical. You can really see this in starfish and brittle stars, also urchins when their spines fall off. They also have multiple arms, or appendages, radiating out from the central body, usually occurring in multiples of 5. Each arm (or segment in the sea urchins case) is identical in it's external and internal construction (organs included). Echinoderms also have a very simple nervous system, so simple that they're not considered to have brains. Instead, their nervous system consists of what's called a nerve ring, located around the mouth, with nerve bands running down each arm or appendage of the body. It can not see detailed images but some echinoderms have been studied and proven to be sensitive to light.
It gets better, by the way. Echinoderms can regenerate. And not JUST regenerate, some can even reproduce when harmed, but before I get into that I'll explain regeneration. What this means is that if they get hurt, like a piece of their arm is ripped off, they can grow it back. I know that sounds similar to when we get a cu or a chunk of skin ripped off while skateboarding or something like that, but it's completely different. A good comparison would be if you got a finger chopped off. You can't grow that back, You'd have a stubby finger or any other body part for the rest of your life. In contrast, if a starfish looses a limb, it can grow back entirely! It takes some time and a lot of energy, but they can do it. Now, reproduction upon a limb or such like that gets ripped off is a little more complicated. Regeneration can occur if any amount of a limb is ripped off, but reproduction can only happen if a piece of the nerve ring is severed in the process. So basically, it needs a bit of it's primitive main nervous system to be detached as well. And, POOF!, there appears another identical starfish. A clone. Super cool!

Now! Let's talk about a few of the specific types of echinoderms!

Sea Stars (Starfish) - Asteroidea

Like I said, these guys are one of the most popular of the echinoderms. And for good reason!
Everyone knows about the little suction cup like things that are found on the bottom of starfish and that they're used to move along the surface of whatever they're climbing over, which can seriously be.... anything. But the way that they make those suckers move is pretty cool. On the aboral side (top) of their body, there is a little hole that opens and closes to allow water to pass in and out of the ring canal (which is different from

The ampulla, on top of the tube feet, act like turkey
basters, squeezing and relaxing to force water
into the tube feet to make them move.

the nerve ring) and spread out to the radial canals. The whole is usually a different color than the rest of the starfish and looks like a large pore. They use these canals to create a vascular system of hydraulic pumps, pumping the water in and out of each tube foot to extend or retract them independently. For an animal that doesn't have a brain, I'd say that's reeeaaaaaaally impressive. On top of that, they don't only use those tube feet to "walk", they also TASTE and breath with them. They taste chemicals on surfaces and in water with the ends of their tube feet to help them find food and to avoid toxic areas, on top of exchanging oxygen and carbon dioxide through the "skin" of the them. Imagine being able to taste and breath with your feet..... It's not really a pleasant thought.

That white stuff you see is the starfish's stomach... not food.

Now for a bit of, well, gross. How they eat. I'll keep this short because it is pretty gross but it's still really cool. Starfish, instead of just popping things into their mouths, which are pretty small by the way, actually excrete their stomach's onto their prey. Yes, you read that correctly, they throw up their stomach in order to eat. They then partial digest their food and.... *shiver*..... slurp up their digested food. Sounds delicious, right? It's gross. Cool... but incredibly gross. But, it does give them a bit of an advantage because then they can eat larger fish and gorge on food in one sitting instead of using their energy to hunt for large amounts of small bits of food.



I'll let you ponder the awesomeness and.... weirdness that are Starfish and bombard you with more Echinoderm information a little later. I hope you enjoyed and are a little more excited about starfish and their brethren!
I'll just leave you with this video I took of a super tiny starfish wiggling it's little tube feet at the aquarium, Biomes, that I volunteer at!

Coming up: Part 2: Brittle Stars and Sea Cucumbers!!

Keep an eye out for it!

Octopus picture: http://motor-kid.com/cartoon-sea-cucumber.html

Starfish circulatory system: https://yhsbiology.wikispaces.com/Echinodermata

Starfish eating: https://lizwason.wordpress.com/category/2013/02-february-2013/

Thank you all for your pictures!