2. In which environments do echinoderms live?
Echinoderms are marine animals. They live in salt water.
3. What are the basic morphological features of echinoderms?
Echinoderms, as their name indicates (echino = spiny, derma = skin), are creatures with spines that stick out from an endoskeleton. Their endoskeleton is made of calcareous plaques that, in addition to spines, contain pedicellaria, small pincers used to clean the body and to help capture prey. They also contain a hydrovascular system known as the ambulacral system. Adult echinoderms have pentaradial symmetry; the radial symmetry in these animals is secondary, as it is present only in adults.
4. How can the endoskeleton of echinoderms be compared to similar structures among vertebrates, arthropods and molluscs?
The skeleton of echinoderm is internal; that is, it is an endoskeleton. It is made of calcium carbonate (calcareous).
Vertebrates also have an internal skeleton made of bones and cartilage. Arthropods have an external shell made of chitin, a chitinous exoskeleton. Some molluscs have a calcareous shell that functions as an exoskeleton.
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5. What system allows echinoderms to move around and attach to certain substances?
The system that allows echinoderms to move and to attach to substrates is called the ambulacral system. In these animals, water enters through a structure called the madreporite, passes through channels and reaches the ambulacral feet along the undersurface of the body. In the ambulacral region in contact with the substrate, there are tube feet which empty and fill with water, thus acting as suckers.
6. What type of digestive system echinoderms contain?
Echinoderms contain a complete digestive system, with a mouth and anus.
7. Do sea urchins have teeth?
Sea urchins have a teeth-like structure attached to the mouth and made of five teeth connected to ossicles and muscle fibers. This structure, known as Aristotle’s lantern, is use to scratch food, mainly algae, from marine rocks.
8. What characteristic of echinoderm embryos makes this phylum evolutionarily resemble chordates?
Echinoderms and chordates are deuterostomes, meaning that, during their embryonic development, the blastopore turns into their anus. All other animals with complete digestive system are protostomes, meaning that their blastopore turns into their mouth.
The blastopore is the first opening of the digestive tract to appear during embryonic development.
Phylum Echinodermata Review - Image Diversity: blastopore
9. Do echinoderms have respiratory and circulatory systems?
In echinoderms, respiratory and circulatory systems are not well-defined (with the exception of the holothurian group). The ambulacral hydrovascular system carries out the tasks of these systems.
10. Do echinoderms have an excretory system? How is excretion carried out in these animals?
Echinoderms do not have an excretory system. Their excretions are eliminated by diffusion.
11. How can the symmetry and the nervous system be described in echinoderms?
Adult echinoderms, along with cnidarians, present radial symmetry, meaning that their body structures are distributed around a central point. However, the radial symmetry in echinoderms is secondary radial symmetry, since their larval stage has bilateral symmetry and the radial pattern appears only in adult specimens (there are a few adult echinoderms with lateral symmetry). All other animals have lateral symmetry with the exception of poriferans (they have no defined symmetry).
Echinoderms do not present cephalization. They have a diffuse network of nerves and neurons made of a neural ring around the mouth and radial nerves that split off into branches to follow the pentaradial structure of the body.
Reproduction in Echinoderms
12. Do echinoderms use internal or external fertilization? Are they divided into separate sexes?
Fertilization among echinoderms is external, as gametes are released into the water, where fertillization occurs.
The majority of echinoderms are dioecious, containing both males and females.
13. Do echinoderms have a larval stage?
In echinoderms, embryonic development is indirect, with ciliated larvae.
14. Into what classes is the phylum Echinodermata divided?
The five classes of echinoderms are: asteroids (starfish), ophiuroids, crinoids, holothuroids (sea cucumbers) and echinoids (sea urchins and sand dollars).
Summary of Echinoderms
15. The main features of echinoderms. How can echinoderms be described according to examples of representative species, basic morphology, type of symmetry, germ layers and coelom, digestive system, respiratory system, circulatory system, excretory system, nervous system and types of reproduction?
Examples of representative species: sea cucumbers, sea urchins, starfish. Basic morphology: calcareous endoskeleton with spines, ambulacral system. Type of symmetry: secondary radial. Germ layers and coelom: triploblastics, coelomates. Digestive system: complete, deuterostomes. Respiratory system: nonexistent. Circulatory system: nonexistent. Excretory system: nonexistent. Nervous system: simple, nerve network without ganglia or cephalization. Type of reproduction: sexual, with a larval stage.