Surely you have seen a starfish, either in photographs or when you have visited a beach. They are among the most widely distributed marine animals in the world, although most of them live in the depths, so their habits are unknown to many people.
Do you know what do starfish eat? If you are interested in knowing this and other curiosities about these striking marine inhabitants, you can not miss the next item. Keep reading!
Characteristics of starfish
Starfish belong to the Asteroidea class and are invertebrate animals that inhabit the deep sea. They are characterized by a flattened body from which multiple armsprotrude, the number of which varies according to the species, but which ranges between five and fifty limbs. These limbs have sucker cups that they use to move, catch prey, defecate, and breathe. Due to their way of moving, by locomotion, these suckers are called "tube feet".
In addition to their arms, they have a mouth that is located on the flattened part of the body, that is, in the center. Another curiosity about their morphology is that they lack blood, they use a hydrovascular system that pumps water.
The skin of starfish is composed of calcium and can have a grainy, rough, smooth texture and even hard spines. Most of them are distinguished by their bright colors (blue, red, white), although many species also have simple hues to blend in with the seabed.
Where do starfish live?
Do you know where starfish live? They are distributed in the oceans around the world, that is, they can be found in the Arctic, Antarctic, Atlantic, Indian and Pacific. In these oceans, most species prefer to live at 6,000 meters of depth, although some inhabit the sandy bed found along the coasts.
These stars only survive in s alty and brackish environments, so they cannot be found in fresh water. In the ocean, its favorite areas are around coral reefs, kelp forests, and anywhere on the bottom where it finds rocks or muddy sand. Due to their night habits, they can carry out their lives to perfection in environments with low light such as the ocean floor.
Starfish reproduction
Given the curious appearance of these invertebrates, one wonders how starfish are born, right? Actually, there is not much mystery: they present sexual reproduction and asexual reproduction.
Sexual reproduction
Although it is difficult for humans to distinguish, in most starfish species there are individuals male and female Many of them are capable of changing gender as they age, that is, they are born male or female and an exchange occurs when they reach adulthood or old age.
When it is time to reproduce, a starfish releases the gametes (sex cells) through the gonads it has in your arms. As the eggs are released, another starfish releases the sperm to fertilize them. It is even possible that both parts of the process are carried out by the same individual in the case of a hermaphrodite species.
Once the eggs are released, there are several options: they will develop as part of the plankton, the mother will incubate them and protect them with her body, or they will grow adhered to a rock When they reach the right size, the eggs give way to larvae, which swim or float in the sea. As they become adults, their body morphology changes and they begin to inhabit the seabed.
Asexual reproduction
Other species of starfish have an asexual reproductive cycle. Some do not need the intervention of another individual, because at the end of their arms they have the male and female gonads, thanks to this, they are capable of reproducing when some their arms come off for whatever reason, even if the separated piece is a centimeter long.
Another asexual method is budding This process consists of creating an individual that grows attached to the parent and only separates when it is developed. This method is common in starfish larvae found in environments with abundant food.
Types of starfish
In the world there are about 2000 types of starfish,so their characteristics are varied.
- Order Paxillosida: includes 255 species. They do not have suckers on the tube feet. They prefer to live semi-buried in the sand or sea mud. They usually occur in abundance of individuals in the areas they inhabit.
- Order Valvatida: consists of 695 species. They have about five arms with suckers, as well as a visibly calcified body.
- Order Velatida: includes 210 species. They have a hexagonal shape with fifteen arms with suction cups. The body is decalcified and they inhabit cold waters, such as the polar and subpolar regions.
- Order Spinulosida: consists of 120 species. They have a weak skeleton body and arms with suckers. In addition, they have a rough texture full of thorns.
- Order Forcipilatida: includes 300 species. They have a body made up of three pieces and arms with flattened suckers. They have powerful serrated jaws, making them great predators. They prefer cold waters.
- Order Brisingida: includes 111 species. They have between six and twenty arms without suckers. They prefer deep water.
- Order Notomyotida: includes 75 species. They can have arms with or without suckers, accompanied by a muscular body. They inhabit very deep areas.
Starfish Feeding
Now that you know how these curious ocean animals carry out their life cycle, it's time to tell you all about starfish feeding.
Most starfish are carnivorous and predatory, meaning they hunt their prey. Their main food source is crustaceans, sea urchins, smaller fish, plankton, clams, mussels, snails, sea cucumbers, coral polyps, anemones and, basically, any animal slow enough that they are capable of ingesting.
Now then, how can starfish, seemingly white-bodied and helpless, devour such a variety of prey? The stomach of these invertebrates has the quality of being evaginable, which means that they are able to "expel" it out of the body. When facing prey, the star circles it with its arms, whether they have suckers or not, and then expels the stomach so that the prey is covered with digestive juices. This process initiates the decomposition of the victim. Then they simply retract their stomachs and swallow their prey.
Other species, however, feed only on decomposing matter, whether of plant or animal origin. Species that are not able to suck up what remains of the prey after discharging gastric juices, simply devour the animal whole and then the star expels the inedible parts.
In this video from @n2oBlazer on YouTube you can see how a starfish eats a crustacean:
What do sea urchins eat?
The sea urchins are echinoderms commonly found in places that stars also inhabit, so they are predated by them. They are characterized by a round body full of rigid spikes.
Now, what do sea urchins eat? Most of them are herbivorous animals, so they feed on algae that they find on the seabed. Others, however, are detritivores, meaning they eat decaying matter. Similarly, some of them are predators and feed on animals smaller and slower than them.
What do sea sponges eat?
Sea sponges are invertebrates porifera (phylum Porifera). There are about 9,000 species and for a long time they were thought to be marine plants, due to their peaceful life and their appearance that lacks recognizable structures, such as eyes, mouth, etc. These are incredibly simple animals, but at the same time you are surprised by the strange and unique shapes that their bodies adopt.
With regard to feeding, ingest nutrients cellularly, through phagocytosis (cells surround the food particle and break it down to absorb it) and pinocytosis (same process, but takes carried out with fluids instead of solids). Thanks to these processes, they feed on small particles of decaying matter, microscopic algae and marine bacteria.
