The animal world is wonderfully diverse. In it we find a variety of unique characteristics in each of the groups that make it up. Within this are the echinoderms, invertebrate and exclusively marine animals, with traits that only they possess. In this article on our site we will talk about this edge. Dare to continue reading, to find out what the echinoderms are, characteristics, types and examples
What are echinoderms?
Echinoderms are a phylum of marine animals and invertebrates, whose name refers to the external characteristics of their body, as it means « prickly skin. They form a large group, which has about 7000 species, although many more existed in the past. They present unique characteristics linked to their symmetry and their mobility, aspects in which they do not coincide with other animals. Thus, due to its peculiarities, this group has been a study challenge for scientists.
Characteristics of echinoderms
As we have mentioned, echinoderms have traits that are exclusive to this phylum, which makes them peculiar animals. These are its features:
- They are invertebrate animals, formed externally by spines or protuberances of calcareous origin.
- Internally, they also have a calcareous formation, which constitutes the endoskeleton. They can be plates or small structures known as ossicles. In each group the level of development of the internal configuration varies.
- They have a complex aquiferous vascular system.
- Their bodies are star-shaped, round or cylindrical.
- They lack a head and a brain and their specialized sense organs are reduced.
- The sensory system is made up of tactile structures, chemoreceptors, tube feet, terminal tentacles, and photoreceptors.
- Echinoderm larvae have bilateral symmetry, but as adults they have a radial symmetry that is unique in the animal kingdom and specifically pentameric. Although there are other animals with radial symmetry, echinoderms are the only ones to have this characteristic, possessing a complex system of organs.
- They have no capacity for osmoregulation, so They cannot live in brackish or fresh water.
- They have a cosmopolitan distribution, covering various depth ranges.
Reproduction of echinoderms
Echinoderms are animals with separate sexes, but there are some hermaphrodite species. The gonads tend to be large, with simple ducts and an undeveloped copulatory apparatus. Fertilization is external Some species incubate their eggs, while others deposit them in the marine environment.
Once they are fertilized, the development process originates symmetrically bilateral free-living larvae, which will form part of the zooplankton. Subsequently, they go through a series of transformations that result in an adult individual, fully modified to radial symmetry.
Some echinoderms also have asexual reproduction, as they are capable of dividing their bodies, creating two identical individuals. Additionally, certain species have the ability to autotomy and regeneration, so that they can voluntarily detach themselves from a part of the body that, for example, is injured, since they will regenerate it over time.
Echinoderm feeding
Echinoderms feed on various suspended particles in the seas, but they can also be predators, although mainly of species with sessile life because They are usually quite slow. Depending on the species, they feed on marine vegetation, algae, carrion, detritus, marine sponges, molluscs, crustaceans and there are even some that consume other echinoderms.
Echinoderm respiration
These underwater breathing animals have various structures depending on the group. Thus, they can breathe through dermal gills, tube feet, respiratory trees or specialized bags for this process. Therefore, the complex aquifer vascular system and the ambulacral apparatus play an important role in the gas exchange of these animals, through internal transport that occurs through the various ducts of the body.
Classification of echinoderms
Echinoderms have been grouped into five different classes according to their characteristics. This is the taxonomic classification that has been established:
- Asteroidea: these are starfish, with around 1800 species.
- Crinoidea: better known as sea lilies. There are about 600 species.
- Echinoidea: these are the sea urchins, which number around 950 species.
- Holothuroidea: or sea cucumbers, which are about 1400 species.
- Ophiuroidea: also called brittle stars, of which there are about 2000 species.
Types of echinoderms
As we have seen in its classification, there are five types of echinoderms. We see them in more detail:
- Starfish: they are the typical star-shaped echinoderms, with a central disc from which five or more arms emerge that they possess. Many species of starfish exhibit beautiful colorations.
- Sea lilies: they owe their name to their resemblance to said plant, since its arms, attached to a stem, simulate the petals of a flower or the branches of plants. Although many have the possibility of mobilization, they generally remain fixed to the substrate.
- Sea urchins: they can be balloon or disc-shaped. They lack arms but have a body made up of an external skeleton covered with their peculiar spines or spikes with the possibility of mobilization.
- Sea cucumbers: this type of echinoderm breaks with the globular or star shape of the previous cases. On the contrary, these animals have a soft and elongated body Although externally they do not coincide with the secondary radial symmetry of echinoderms, internally they are composed of systems with multiples of five.
- Blisterbreads: they are sometimes mistakenly called starfish because of their similar appearance. However, their sizes are smaller and from the central disc come five arms that are thin and long.
Examples of echinoderm animals
Next, let's learn about some specific examples of echinoderm animals.
Common Starfish (Asterias rubens)
This starfish is preferentially distributed in the northeastern Atlantic Ocean. It is characterized by having five blunt-ended arms and a body covered with calcareous protuberances. The largest individuals reach about 50 cm.
Marble Star (Fromia monilis)
This echinoderm inhabits the Indian and Pacific oceans. It has a central disk in different shades of red from which the five arms come out. It has some cream-colored, non-spiny bumps that give rise to its common name, as they look like marble tiles.
Giant Feather Star (T ropiometra carinata)
It is a species of sea lily that can have different colors, such as yellow, orange, brown and even black. It has a cup-shaped disc and is made up of ten arms. He has mobilization capacity, in a movement that is quite attractive due to the way he moves his arms.
Mediterranean Comatula (Antedon mediterranean)
This echinoderm is another species of sea lily. It also has a cup-shaped disk with ten arms, but in this case, five arms are more branched It has structures known as pinnules. They are preferably located at about 40 meters, although they can be at greater depths, mainly on rocky bottoms.
Sea urchin or chestnut (Aracentrotus lividus)
Inhabits the Mediterranean Sea and the eastern Atlantic Ocean. It generally has a purple coloration and is characterized by having a flattened ventral area. It reaches a diameter of up to about seven centimeters and the body covered with long spines.
Fire urchin (Astropyga radiata)
This sea urchin is characterized by having a flat or slightly concave aboral side. It is a type of large hedgehog, about 20 cm long, with long spines, about 4 cm long. It is distributed throughout the Indian and Pacific oceans, generally in sandy depths of up to 70 meters.
Donkey manure (Holothuria mexicana)
It is a species also known as Michelin sea cucumber that is distributed in the Caribbean Sea and in an archipelago of Portugal. Its external coloration is brown or gray, with opaque tones, while, internally, it is orange or reddish. It is a cucumber that manages to reach up to about 50 cm in diameter
Chocolate chip sea cucumber (Isostichopus badionotus)
The reason for its common name is clear, since it is a cucumber with a series of brown spots that look like sparks of chocolate. It can reach 45 cm in length. The base color is cream, orange or brown. It has a wide distribution in the warm areas of the Atlantic Ocean.
Basket Star (Astrophyton muricatum)
It is an echinoderm of the brittle star group that lives in the Caribbean Sea and the Gulf of Mexico. Its coloration tends to be brown to black and is characterized by the fact that during the day it keeps its eight arms folded, but at night it extends them completely, reaching around one meter in length. It does this in order to filter feed.
Common Brittle Star (Ophiura ophiura)
This species of brittle star usually inhabits seabeds off the coasts of northwestern Europe. It has five thin arms, about 14 cm long, around a small central disk. It tends to be brown to reddish in color, with a light underside.
