Echinodermata

Echinodermata image
What is Echinodermata and how do they move and defend themselves?
  • Echinoderms are marine vertebrates which includes starfish, sea cucumbers, sea urchins etc. they contain about 7000 species and 13,000 extinct species. They are mostly found in habitats such as shallow intertidal areas to abyssal depths. They mostly walk in manners such as crawling or walking through the seafloor but some species use their spines to move. When they are crawling they pump seawater through their internal body canals and the water is used to inflate the feet of the tube and causes them to expand but in some species tube feet are equipped with suckers that grip onto the sea floor. Echinodermata defenses are powerful and well developed. Their defense strategies include spines, toxins which can be delivered through tubed feet. 
The illustration shows a sea star, which has a mouth on the bottom and an anus on top, both in the middle of the star. The disk-shaped stomach is sandwiched between the mouth and anus. Two tubes radiate from the stomach to each arm, and many small digestive glands connect to these tubes. Beneath the stomach is a central ring canal that also connects to tubes that extend into each arm. Tube feet are attached to these tubes. Each tube foot resembles a medicine dropper, with a bulb-shaped ampulla at the top and an extension called a podium at the bottom. The bottom of the podium protrudes from the bottom of the starfish. There are many podia along the length of the arm, which allow the sea star to latch onto objects and walk. A structure called a madreporite connects to the central ring, and protrudes from the upper surface of the sea star, next to the anus.

How does starfish locomotion work?

  • The underside of the starfish is covered with thousands of tube feet, which helps it to move and tingly grip on the floor. To move each tube, feet swing like a leg lifting up and forward, that attaches itself to the ground  at the tip of the feet is the suction cup.  The vascular system helps set the hydraulic pressure, which pulls the water. All the tube feet have a swollen structure called an Ampulla. The podium consists of suckers to help starfish to attach to the ground. When the water is pulled inside, it travels from the madreporite through the stone canal, the ring canal, the radial canals, and finally, the lateral canals. This then reaches the Ampulla, where the water is preserved at all times. When the ampulla contracts, it forces the water towards the suckered podium, which results in their extension.once the starfish reaches the position where it wants to relax the ampulla will also relax.This relaxation causes the formation of suction cups. The suction cups forms a vacuum and help to attach the sea star to the surface. After both the steps are completed, the sea star has reached an entirely new location. With these little feet, starfish can move at a speed of 60 feet per hour. This is a slow process but effective.
How Starfish Move

How do starfish defend themselves?

  • Some of starfish defense strategies are tube feet, burrowing, and releasing arms. Straight moves by pushing the water with its tube feet. The tubed feet with rippling effects and this helps the starfish to move faster. By moving faster the starfish could get away from its enemy easily. Starfish can dig sand and spray sand at predators eyes and burrow and throw the sand on their bodies when they feel threatened. Starfishes have the power of regeneration. It can drop off the arm that has been grasped by the predator. The starfish can separate its arms from its predator and generate another arm to replace the bitten arm.  Starfish can also camouflage with the coral reefs and also developed spiky skins, which are unpleasant for the predator to consume. Also slime texture skin that these starfishes have can eject mucus at predators. These all defenses help starfish against its predators.
Starfish (Sea Stars) | National Geographic

How do sea cucumbers move?

  • Sea cucumbers can move on the surface through sand or mud using  peristaltic movements. Some sea cucumbers contain tubed feet, which helps to creep like starfish. Some sea cucumbers pull themselves with the help of buccal tentacles and others can expand to contract their bodies. Burrowing sea cucumber uses contraction of body muscular walls and moves sand or made out of the way using tentacles. 
5 Reasons Sea Cucumbers Are the Best Kind of Cucumber

How do sea cucumbers defend themselves?

  • Some sea cucumbers have clusters of cuvierian tubules which they will  eject as sticky threads from their anus and intertwine and permanently disable the attacker. The respiratory tree in the gut contains these tubules. When startled, these cucumbers may expel the tubules through a tear in the wall of the cloaca. Along with tubules they eject a toxic chemical called holothurin, which could kill the predator. Some sea cucumbers will spew intestine walls and expel their guts and respiratory tree. They are very long and sticky. This substance will get stuck to the predator and the predator will unlike the meal and get away from that place. Sea cucumber can regenerate respiratory tree, guts and intestine wall later.
A Sea Cucumber's Defense: Expelling Its Gut & Genes - BioTechniques
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