Starfish belong to the phylum echinoderms, class asteroidea, made up of more than 7000 species of animals,all of marine origin There are no known species of echinoderms that live in fresh water, as they need s alt water for osmotic regulation of their body. Other well-known groups of echinoderms are sea urchins and sea cucumbers.
In this article on our site we will review the life cycle of the starfish, we will talk about their body characteristics, how they move, what and how they eat and other very curious facts such as, for example, are starfish hermaphrodites?
The skeleton of the starfish
Starfish have an endoskeleton made up of plates, called ossicles or sclerites. It is a common feature of all echinoderms. The animal has a layer of epidermal tissue below which we find the dermis, where the ossicles of calcareous origin are immersed, which, in starfish, articulate with each other. Normally these ossicles have spines or bumps that give the animal a spiky look
How do starfish move?
One of the adaptations of starfish and all echinoderms is that they have an aquifer or ambulacral system, which serves them to move, catch food, and breathe. This system consists of a set of tubes or internal channels that are associated with appendages, or tube feet, on the surface of the animal.
These canals are filled with seawater. In the dorsal area of the starfish there is a plate called madreporito, which communicates with the outside with the star's ambulacral system, this is where the water enters the set of ducts. The water finally comes out through the tube feet.
This system works in the same way as the hydrostatic skeletons (hydroskeleton): it takes water from the external environment through the madreporite and the pressure generated in the internal system of cavities serves to move the tube feet.
Starfish nutrition
The digestive system consists mainly of a mouth in a ventral position, that is, the mouth of starfish is below their body, in contact with the ground. They also have a stomach that can be reversed, making its inner surface become outer, and a short, straight intestine that ends in an anus, which may not exist.
Starfish that cannot push their stomach out of the body, must feed on small particles or small animals or vegetables. Likewise, the stars that can invert their stomach can feed on much larger prey, such as fish or molluscs, since stomach digestion takes place outside the Body.
Starfish reproduction and their life cycle
To better understand the life cycle of starfish we must know that these echinoderms have sexes dioecious, that is, there are male and female individuals, there are hardly any hermaphrodite species. They have a complex reproductive cycle, the new individuals go through two stages before settling on the seabed as adult starfish.
1. Fertilization and formation of the zygote
Starfish have external fertilization, so both males and females release their eggs and sperm, respectively, by Exterior. These sperm and eggs contact each other in the marine environment causing fertilization of the eggs and subsequent formation of the zygote
Some species can reproduce throughout the year and others only do so at specific times.
two. Larval stage
Once the zygote has formed, it transforms in a few minutes into an embryo and from here, a larva is not created. too much time passes.
Starfish have five different types of larvae depending on the species: bipinnaria, brachiolaria, brachiolaria, barrel-shaped larva and larva without brachiolaria. Some species will only have one type of larva during their juvenile development, and other species will have several larval forms during their development.
These tiny larvae wander as planktonic organisms for days or weeks in the ocean, feeding on plankton smaller than themselves. In some cases, the last larval stage before entering the juvenile stage does not need to feed and simply wanders until it finds the appropriate place to settle.
Species without larval stage
Some starfish do not have a larval stage during their development. Instead, it has a phase called mesogen. These stars go directly from embryo to juvenile.
3. Juvenile Status
Through a metamorphosis, if there is a larval stage, or by morphogenesis, if the species goes through the mesogen phase, the small individuals become juveniles. They will already have the adult form, but a smaller size and will not be fertile yet.
Some studies suggest that the larvae or mesogens are attracted by the pheromones released by adult individuals of their species to establish themselves in the most appropriate.
4. Adult Status
After a while, the juvenile will have reached the weight of the adult starfish and will be able to reproduce. As we said, starfish have separate sexes and reproduce via sexual reproduction, although some species can reproduce via asexual reproduction It is unusual, and usually occurs at adverse times, for example when a predator attacks them.
If they lose one of their arms, it could give rise to a new star genetically identical to the original. In addition, the original will be able to grow a new arm.
More about starfish
Now you know about the life cycle of starfish, their reproduction and life stages. Do you want to know more about marine animals? Then we invite you to discover which are the endangered animals of the Great Barrier Reef, starfish being one of them.
