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Phylum Echinodermata Review
1. What are some representatives of the echinoderm phylum? Starfishes, sea cucumbers (holothurians), sea urchins and brittle stars are examples of echinoderms. Phylum Echinodermata - Image Diversity: echinoderms starfish sea cucumber sea urchin brittle star 2. Under 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 the name indicates (echino = spiny, derma = skin), are creatures with spines originated from an endoskeleton. Their endoskeleton is made of calcareous plaques that besides spines contain pedicellaria, small pincers used to clean the body and to help the capturing of prey. They also present a hydrovascular system known as the ambulacral system. Adult echinoderms have pentaradial symmetry; the radial symmetry in these animals is secondary, present only in adults. 4. How can the endoskeleton of echinoderms be characterized in comparison to analogous structures present in vertebrates, arthropods and molluscs? The echinoderm skeleton is internal, i.e., it is an endoskeleton. It is made of calcium carbonate (calcareous). Vertebrates also have internal skeleton made of bones and cartilages. Arthropods have an external carapace made of chitin, a chitinous exoskeleton. Some molluscs present a calcareous shell that works as exoskeleton. 5. What is the system that permits movement and fixation to echinoderms? The system that permits movement and fixation to substrates in echinoderms is called the ambulacral system. In these animals water enters through a structure called madreporite, passes through channels and reaches the ambulacral feet in the undersurface of the body. In the ambulacral region in contact with the substrate, there are tube feet filled and emptied by water thus acting as suckers. Phylum Echinodermata - Image Diversity: ambulacral system 6. What is the type of digestive system of echinoderms? Echinoderms present a complete digestive system, with mouth and anus. 7. Do sea urchins have teeth? Sea urchins have a teeth-like structure juxtaposed 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 is the embryonic characteristic that evolutionarily makes echinoderms proximal to chordates? Echinoderms and chordates are deuterostomes, i.e., in their embryonic development the blastopore turns into the anus. All other animals with complete digestive system are protostomes, i.e., their blastopore originates the mouth. The blastopore is the first opening of the digestive tube that appears in the embryonic development. Phylum Echinodermata - Image Diversity: blastopore 9. Do echinoderms have respiratory and circulatory systems? In echinoderms there are not well-defined respiratory (with the exception of the holothurian group) and circulatory systems. The ambulacral hydrovascular system plays the function of these systems. 10. Do echinoderms have an excretory system? How is excretion done in these animals? Echinoderms do not have an excretory system. Their excretions are eliminated by diffusion. 11. How are the symmetry and the nervous system characterized in echinoderms? Adult echinoderms, along with cnidarians, are the animals that present radial symmetry, i.e., their body structures are distributed around a center. The radial symmetry in echinoderms however is a secondary radial symmetry, since their larval stage has bilateral symmetry and the radial pattern appears only in adult individuals (there are some few adult echinoderms with lateral symmetry). All other animals have lateral symmetry with exception of poriferans (no symmetry is defined for them). Echinoderms do not present cephalization and they have a diffuse network of nerves and neurons made of a neural ring around the mouth and of radial nerves that ramify to follow the pentaradial structure of the body. Phylum Echinodermata - Image Diversity: radial symmetry 12. Do echinoderms present internal or external fecundation? Is there sex division among individuals? The fecundation in echinoderms is external, gametes are liberated in water where fecundation occurs. The majority of echinoderms are dioecious with male and female individuals. 13. Is there a larval stage in echinoderms? In echinoderms embryonic development is indirect, with ciliated larvae. 14. What are the classes into which the phylum Echinodermata is divided? The five echinoderm classes are: asteroids (starfishes), ophiuroids, crinoids, holothuroids (sea cucumbers) and echinoids (sea urchins and sand dollars). 15. Echinoderm identity card. How are echinoderms characterized according to examples of representing beings, 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 representing beings: sea cucumber, sea urchin, starfishes. 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. Types of reproduction: sexual, with larval stage. |