THE STARFISH
- Friendly Fins
- Dec 2, 2024
- 5 min read
Updated: Mar 8
“You have known me since you were children! I am among the first marine animals that you most easily encounter underwater”
Who is the starfish?
With its unmistakable shape, everyone knows the starfish and everyone can recognize it, or at least recognize the most common species, but think that there are about 1500 different species! Let's get to know these strange creatures better:
“First of all you should know that I am an animal and one with a strong character too!”
It has a unique symmetry: it is pentamerous, that is, the body parts are distributed along five rays around the oro-aboral axis. What is it?...
Its shape does not allow us to define a head and a tail but rather an oral side, where the mouth is located (towards the bottom) and an aboral side where the anus is located (towards the top).
They have a central disk from which 5 arms branch out but it can also have 6 or many more!
They can have thin, well defined arms or rather stubby arms like the cookie star in the photo here! Or even have the arms one with the body like the cushion star!
It comes in a variety of colors: from the classic red starfish that we all know, to brown, gray, orange, to the rare blue starfish from Madagascar.
“We are truly very varied, for all tastes, really!”
Strange cousins
The starfish is part of the echinoderms. Within this group we find many different creatures: sea urchins, sea cucumbers, sea lilies, brittle stars and starfish. What do these apparently different animals have in common?
A very ingenious aquifer vascular system for movement: it is made up of a series of water-filled channels that extend outwards via projections called ambulacral pedicels, passing through openings in the calcareous skeleton.
“The ambulacral pedicels are made of a small bulb filled with water and a kind of suction cup that comes out of our body. These, by inflating, allow us to move on the seabed! We also know how to regulate them and therefore decide where to go!”
The skeleton of echinoderms is made up of bony plates called ossicles and these can also be modified to form spines, fixed or articulated, which protrude from the body, as in the case of sea urchins and spiny stars.
“When we die, our calcareous skeleton is often washed ashore by waves and currents, so you can easily find it on the beach! Leave it there though, because as it crumbles it can give life to new and extraordinary things!”
Where the starfish lives
Starfish live on rocky but also muddy and sandy seabeds, depending on the species. They can live in tropical and temperate seas all over the world, as they are particularly adaptable.
We will find them apparently immobile and in the shade while they rest, waiting for the night to hunt.
“Don’t be fooled by our calm and peaceful appearance… We are very hungry predators!”
How and what does the starfish eat?
This bizarre animal has its own way of feeding: to begin with, its stomach is divided into two regions:
The first larger one that receives the food ingested by the mouth
The second smaller one with digestive and absorbent function that branches into the arms.
Starfish feed on a variety of animals including crustaceans, corals, detritus, shelled mollusks such as gastropods (snails) and bibalves (mussels, clams, etc.).
So far so good, but…
Many starfish are able to feed on bivalves in a very particular way: thanks to the muscles in their arms, they are able to wrap themselves around the bivalve and open its shells (valves).
Even a small opening of 0.1 mm is enough to allow the first part of their stomach to come out of the mouth and throw itself inside the bivalve, starting to digest it thanks to its powerful digestive enzymes!
“it's much more comfortable, isn't it?!”
Afterwards, the exhausted bivalve will be forced to loosen its grip and therefore open completely, allowing the animal to digest its food completely.
Once the snack is finished, the stomach goes back inside thanks to the action of special muscles.
Starfish Regeneration and Reproduction
“We are very famous for our high regenerative power”
Equally unique is their regeneration: in fact, they are able to regenerate any part of a broken arm, for example. It is a very slow process, however, it takes almost a year to complete it. Even from an arm a new star can be generated, the important thing is that it has at least a small portion of the central disk.
As for reproduction, they can reproduce both asexually and sexually:
Asexually they can do this thanks to regeneration; in fact it is achieved by the division of the central disk followed by the growth of all the missing parts.
Starfish have separate sexes, although they are indistinguishable from the outside. Sexual reproduction occurs by external fertilization of gametes released into the water.
“When a female star releases her gametes, she immediately releases pheromones (hormones) that induce other stars in the area to release theirs, thus increasing the chances of fertilization!”
What does the starfish feel?
The starfish has a nervous system that allows it to do a lot of things. First of all, it is composed of a nervous ring around the mouth and radial nerves that extend into each arm.
“Look how we can surprise you!”
The nerves coordinate the pedicels which in turn determine the movement of the animal.
They are able to clean their bodies thanks to pincer like structures called pedicellariae that are located on the aboral part of their bodies (above)! What are they supposed to clean themselves from?
“For example, from grains of sand, algae, some parasite that thinks it can settle in!”
They have sensory receptors throughout the surface of their body that allow them to respond to light, chemical and mechanical stimuli.
“Therefore we have total control over our body and we are able to perceive everything around us, even you!”
Starfish breathe thanks to small gills that emerge from the ossicles, called papules.
Friendly Fins Tips
As we have just seen, starfish have a very efficient nervous system, could it be interesting to know?
Absolutely! Because they are among the animals that come into contact with humans the most, whether it is while bathing, snorkeling, or diving. They are animals that breathe in water, like we breathe on land, no one would appreciate someone holding them underwater for a few minutes while taking selfies, right?
Let's remember that respect for nature must always win over our curiosity, so here are some tips to get in touch with starfish in the best way:
Let's avoid touching them, they are sensitive to touch and we could create considerable stress for them, furthermore we could cause damage to their body with the pressure of our hand.
Do NOT take them out of the water because they die of asphyxiation.
Be careful how we move underwater! Even fins are part of our equipment and we must move with caution so as not to cause damage to the delicate environment in which our starfish friend lives!
We do NOT fish starfish! This practice, which was widely used for souvenirs in the past, is now an old fad! Many starfish have been brought to the brink of extinction! Some species are more numerous as ornaments in homes than in their natural habitat.
Starfish also actively contribute to the balance of the ecosystem in which they live, their absence could have devastating effects on that particular habitat.
“It is better to admire our beauty in the water, to be kidnapped by the magic of the sea; out of the water we lose all our splendor, we will no longer be able to give you emotions”
Now all you have to do is come and meet us! Find out which starfish live in the Maldives! Click here!
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