Sea stars or starfish are some of the most distinguishable marine creatures on our planet. They belong to the family of echinoderms in which they are a close relative of the sea urchin and crown of thorns fish. However, when it comes to their lives, all we know is that they are star-shaped fishes living in coastal waters and beaches.
So, how do starfish reproduce? Do they have a courting stage? Or do they have a unique reproductive cycle that makes them an interesting one to look further? If you are wondering how starfish reproduce, you have come to the right spot as we will be discussing the sea star reproduction cycle.
Everything About Sea Stars
As we’ve mentioned, sea stars belong to the family called echinoderms. These echinoderms include a class of animals called marine invertebrates and aren’t fish despite their names. What makes them not fishes is that they don’t have any gills used to breathe nor fins to propel them in the water.
There are around 2,000 species of starfish around the world. These species have radial symmetry, which means their body parts are located around a central axis. As a result, radially symmetric animals don’t have left or right. Instead, they have top and bottom.
As you may have already encountered, that sea star’s morphology features five arms around a central disc.
In addition, the upper part of a starfish is usually spiked or made up of rough patches that overlap the plates. Another thing that makes these species quite popular is their vibrant colours, and a starfish can exhibit deep and dark colors such as pink, red, orange, and even pink. In some species, they also exhibit a dark brown or greyish hue in their bodies.
Another thing about their morphology is that the upper part of their bodies consists of calcified and bony skin, making it sort of spiky. Their colors primarily mimic coral reefs to avoid predation. Furthermore, there are no freshwater sea stars, and they are all purely marine animals.
What makes sea stars unique in their ways is their ability to regenerate whenever a body part is severed. They can even regenerate their entire bodies. But this would take a couple of months before it has fully grown identical to the lost one. This is possible because all of their vital organs are stored in their arms. It is believed that starfish can regenerate any parts of their body as long as the central part is intact and not damaged.
They, too, have a remarkable way of eating their food. Instead of biting their food and chewing them, a sea star consumes its food from outside of their bodies. The way starfish eat their food is with their tube feet.
They pry open the shells of clams and oysters, and their stomach erupts from their mouth and goes out onto the shell. After that, the entire stomach of the starfish envelopes its prey and devours it. Once the food is done, their stomach returns to their body.
Sea Star Reproduction
Another unique feature is how starfish reproduce. They are known to exhibit external fertilization, which means the male and female are required to spawn their eggs onto the water.
When the sperm and egg meet in the water, it then fertilizes. Once fertilization is successful, these will develop into eggs and wrap the zygote around. They usually look like a lump of clouded milk that gathers near the surface of the water. There are also other species of starfishes that seasonally spawn and last throughout the season.
Although different sea star species showcase different patterns of development, it follows through the same cycle. When a zygote is formed, it then further develops into bilateral larvae, which they call bipinnaria.
During this stage, these larvae feed on organisms much smaller than them, such as planktons. They feed on these microorganisms for a few weeks. Before they settle in their non-feeding state, this state is called brachiolaria.
Development into Adulthood
Once the adult starfish has settled into the seabed and its habitat, their body should already be radially symmetric. It is also believed that during these stages of their lives, the brachiolaria searches for sea beds that have adult pheromones in their surroundings. This is a tell-tale sign that it is a viable place to live and reach adulthood. Once they have settled into this habitat, they will grow into full-sized adults, as we often see near coastlines and beaches.
Aside from intentional reproduction, sea stars have also the ability to asexually produce. This means that they can produce gametes without relying on a species of the same kind to reproduce. This phenomenon occurs whenever they see that the conditions are quite unfavorable for them. Although, unfortunately, due to their morphology, they are at the bottom of the food chain and are always preyed upon.
When battling predators, they may experience severed arms or lose them entirely. Amazingly, sea stars can regenerate their arms as well as severed arms. In some cases, the severed limbs can grow and become a new star. That’s the case of asexual reproduction, when you don’t have to rely on eggs and sperm to produce.
There is also a rarity among starfishes that they are hermaphrodites, which means they possess both sexual organs in one body. When a starfish is hermaphrodite and is reproducing, this means that they won't go into the larval stage as their environment won’t allow for eggs to be expelled freely into the water. So instead, when a hermaphrodite reproduces, it goes directly into the bipinnaria stage.
Now that you know the sea star reproduction cycle, I’m sure you are amazed at how starfish reproduce. Some sea stars expel their sperm and eggs and form larvae, eventually, hatch and reach adulthood. There are also sea stars capable of producing new ones in the form of asexual reproduction in which severed limbs can form into a new one. Finally, in bizarre cases, there are sea stars who can reproduce all by themselves. Quite amazing, right? I’m sure they are!
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