How do Echinoderms move? – (Locomotion in Echinoderms)
Here, in this post, we will learn about locomotion and movement in Echinoderms. They all are marine colourful organisms with unique shapes and are highly adapted to move in marine water.
As they can be seen moving in sea depths as well as in the intertidal zones of the oceans with the help of their dedicated but simple locomotory organ known as the tube feet.
Their tube feet aids in locomotion. Tube feet also aids them in attaching to the substratum firmly so that they don’t get washed away due to the rapid ocean currents.
Actually, there is a system of fluid-filled canals inside all echinoderms’ bodies with the many external projections being tube feet.
This fluid-filled system helps in adjusting the water pressure inside the animal’s body.
Here, in this post, we will learn more dedicatedly about how the echinoderms move. So, let’s get started.
How do Echinoderms move?
Echinoderms move with the help of their tube feet and water vascular system. They also use their spines which are present in some of the echinoderms like Asteroids and Echinoids along with their tube feet for locomotion and movement.
There are many species of Echinoderms that can also move due to the contraction and expansion process of their body, just like in Sea Cucumbers.
Some Echinoderms can use both of their tube feet along with the process of contraction and expansion of the body for movement.
Some Echinoderms like the unstalked crinoids (feather stars) are known to swim by causing the up and down alternation of their arms in a coordinated way. They can also make their arms in a parachute pattern for going deep into the water.
While there are some Echinoderms like those of the Stalked crinoids (sea lilies), whose adult forms remain firmly fixed to a surface by structures at the ends of the stalks called holdfasts. They are so sessile in nature, meaning that they are not free to move naturally at all.
So, we can also state that almost the majority of the Echinoderms are able to move and locomote from one place to another. While there are only a few species that can’t swim at all.
Nevertheless, whatever may be the cause, they all have the water vascular system in their body which is composed of canals and sub-canals branched all throughout their body.
This water vascular system pumps water along with the nutrients through their bodies and also in setting up their body’s hydraulic pressure aiding in their movement.
Just for example, if we consider Starfish then we must know that the Starfish move by the combined action of their tube feet. The hydraulic pressure inside the Starfish causes the vacuum action of the tube feet suckers aiding in their movement.
So, in the end, we can state that coordinated waves caused by tube feet due to the hydraulic pressure of the water vascular system cause contractions and relaxations of the body resulting in the animal moving slowly.
Also that, some species use their arms and spines for movement as well.
We’ll learn more about this in detail. So, just keep reading…
What is the function of water vascular system in the movement of Echinoderms?
As already stated above that the Water Vascular System is a system of canals that maintains a hydraulic system inside the Echinoderm’s body.
This system is used by echinoderms for locomotion and movement, transportation of oxygen, nutrition, and also in respiration. Here, in this section, we’ll discuss how this system is helpful in the movement of Echinoderms.
The water vascular system is actually composed of numerous canals that get branched and sub-branched inside the body of the echinoderm. The flow of the canals is connected to the numerous tube feet.
This system is actually a part of the coelomic cavities of echinoderms. And also that this system is equally developed in all Echinoderms.
Now, it is also to be noted that the structure and make-over of the canals vary amongst the Echinoderms. The exact structure of the system varies somewhat between the five classes of echinoderm.
The primary function of the water vascular system is to cause locomotion and movement in the Echinoderms. So, that’s why it’s said that it is primarily locomotory in function.
Actually talking about the tube feet, then we must know that as the seawater enters the canal system of the water vascular system it makes its way towards the ampulla of the tube feet.
As a result, due to the pressure of the water the ampulla contracts, squeezing water down into the tube feet. This results in a hydraulic pressure to hold the substratum using the sucker of the tube feet.
To retract the tube feet, the ampulla relaxes. So, the extension and retraction of the tube feet result in the movement of the starfish.
So, it can be thus stated that the extension and retraction of the tube feet are due to the hydraulic pressure generated inside the canal system of the water vascular system leading to the movement and locomotion of the echinoderm.
How fast do echinoderms move?
The speed of the echinoderms mostly varies between species. Species like Sunflower sea star (a type of starfish) can move at a maximum speed of 1 m/min (3.3 ft/min). While there are some Sea Urchins that can move with a maximum speed of about 2.50 cm/min.
They are basically dependent on their water vascular system and the flow of water for the speed of their movement.
Actually in Echinoderms, how fast they can move are basically dependent on their body physiology, anatomy, water current, and the hydraulic pressure that is exerted inside their body.
Since these characters vary between species and so, the speed with which they can move also does vary.
They basically show their natural crawling type of movement on the substrate with the help of their thousands of small tube feet which act as suction cups.
Due to this purposeful coordinated movement, they show really a very slow movement.
If we talk specifically about the Starfish, then it is the most famous Echinoderm and so we all must note that they don’t move very fast. In fact, they are slow-moving as compared to the majority of the snails.
Some of the starfish species like the Leather star (Dermasterias imbricata) can manage to move at just a speed of about 15 cm per minute.
In some scenarios, you will often see them (mostly Sea Cucumbers) moving very fast during the times of high sea waves.
That movement is not due to their own biological system, but due to the force exerted by the waves throwing them to the seashore.
Let’s Know How These Echinoderms Move
Locomotion in Star Fish
Starfish move by the combined action of their tube feet. These tube feet (counting about one thousand tube feet or more on one arm) are located in the ventral (oral side) of the starfish below each of its arms.
Each of the tube feet consists of two parts: the ampulla and the podium.
The ampulla is a water-filled sac containing both circular muscles and longitudinal muscle. The podium is the tube-shaped structure containing longitudinal muscle only.
The hydraulic pressure in the water canals of the starfish causes the coordinated pattern of contraction and expansion of the ampulla due to the action of the circular muscles there.
And the podium also attaches and detaches itself from the substratum due to the action of longitudinal muscles present there.
This overall causes the movement in starfish.
Locomotion in Sea Urchins
Sea Urchins can use both their body spines and tube feet for movement. Their primary locomotory organ is the tube feet.
Their tube feet are part of their water vascular system that exerts hydraulic pressure to aid in their suction movement with the help of the tube feet’s ampulla and podium.
Their spines are controlled by their strong muscles that can also aid in their movement.
Actually speaking about the spines, you must know that these spines are connected with the test (their outer skeleton) causing numerous tiny bumps at the spot where the spines are connected.
These bumps allow the spines to rotate extensively around the bump with the help of the skin and strong muscles covering the test which are usually pulled on by the organism to move the spines.
A small contribution is also provided by their teeth that are situated at the center of their spiked, spherical bodies to aid in their movement.
Locomotion in Brittle Stars
Brittle stars use their arms for locomotion. They have four or five or six or even seven arms depending on the species.
These arms are radially symmetrical that coordinate to aid in the movement of the organism.
They basically show snake-like or rowing-like movement by twisting and turning their arms with quick writhing movements all in a coordinated and rhythmic manner.
So, it is also to be noted that they don’t crawl using their tube feet like starfish, but they do use their flexible arms that can be very long to move almost very rapidly.
Their internal skeleton system is finely made up of calcium carbonate plates that superficially look like vertebrae and so are called vertebral ossicles. These ossicles aid in the movement of their agile arms.
Locomotion in Sea Cucumbers
Sea Cucumbers move with the help of their tube feet and the contraction and expansion of their body.
They slow slug-like movement which resembles a small slow-moving nature just like a snail.
It is also to be noted that not all Sea Cucumbers have tube feet. Just like those of the order Apodida and of the family Synaptidae has tube feet that are highly modified into retractile tentacles which are actually larger than the locomotive tube feet.
Now there can be anywhere between ten to even thirty-five of such tentacles present in the organism depending on the species.
And moreover, these tentacles can have a wide variety of shapes depending on the diet of the animal and other environmental conditions as well.
So, these selective species of Sea Cucumbers move with the help of their tentacles (modified tube feet) and by simple contraction and expansion of their body.
Moreover, Scientists have recently found out that these creatures can suck water into their bodies through their anus. This makes them puff like a wide balloon.
Such puffed-up condition allows them to swim and float along with the speedy ocean currents nearly at speeds of up to 50 miles per day.
Locomotion in Sand Dollars
Sand dollars are flattened disk-shaped in nature in accordance with their lifestyle to stay in the ocean bed and remain dug inside the soil.
They use their spines to move around and to dig deep into the sand. Sand dollars have very tiny and soft spines covered with minute cilia.
They use their water vascular system to create hydraulic pressure internally that is required for the movement of their spines externally.
This external movement of the spines aid the sand dollar to move and locomote slowly but easily.
Sand dollars have five sets of pores arranged in a petal pattern that moves the seawater inside their body to create that hydraulic pressure.
So finally, it can be stated that sand dollars are also able to move across the ocean floor using the spines on their underside.
Locomotion in Crinoids
Crinoids use their arms to move. They move their arms up and down in a coordinated fashion just in order to move and locomote in the ocean water.
Here, crinoids are of two types: Stalked Crinoids and Unstalked Crinoids.
Unstalked Crinoids are known to be able to swim, while those of the stalked crinoids are not able to swim because they remain fixed to the substratum by means of a stalk.
So, those of the Unstalked Crinoids usually move by causing the up and down alternation of their arms in a coordinated way by just making their arms in a parachute pattern for going deep into the water.
The unstalked crinoids can use their arms to crawl along the bottom of the sea, and also they are capable of swimming for short distances.
