Echinoderms Honor

Nature Study

Requirements

1. In what environment can we find echinoderms?

   Answer: You find echinoderms exclusively in the marine environment, at all depths — from coastal zones (starfish in tide pools) to the abyssal zone (sea cucumbers at 7,000 m depth). — Echinoderms emerged 540 million years ago in the Cambrian and are exclusively marine because they depend on the water vascular system (canals with seawater). About 7,000 living species exist today, and more than 13,000 fossils have been described in scientific studies.

2. What does the word Echinodermata, the name that characterizes the phylum of echinoderms, mean?

   Answer: You explain that Echinodermata comes from the Greek 'echinos' (spine/sea urchin) and 'derma' (skin) — meaning 'skin with spines.' The name describes the most striking characteristic of the phylum: the presence of a spiny or rough body covering, clearly seen in sea urchins and starfish. — The term was created by Jacob Theodor Klein in 1734 and formalized by modern science in 1830. The spines are extensions of the calcareous endoskeleton (calcium carbonate plates) — a unique characteristic that distinguishes echinoderms from any other existing animal phylum.

3. Cite 4 characteristics belonging to the phylum Echinodermata.

   Answer: You cite: 1) Pentaradial symmetry (the body divided into 5 equal parts); 2) An endoskeleton of calcareous plates (calcium carbonate); 3) A water vascular system (canals with seawater for locomotion and respiration); 4) The ability to regenerate (rebuilding lost parts, such as a starfish's arms). — Pentaradial symmetry is unique in the animal kingdom — only echinoderms have it. The water vascular system uses tube feet (hundreds of small tubes with suckers) to move. Regeneration is so extreme that some starfish regenerate an entire body from a single arm.

4. What type of symmetry do echinoderms have? What does that mean?

   Answer: You explain that echinoderms have pentaradial symmetry — the body is divided into 5 equal parts around a central axis. It means that by tracing 5 lines through the center, each division is identical to the others (visible in starfish with 5 symmetrical arms). It is a pattern unique in the animal kingdom. — Curiously, echinoderm larvae have bilateral symmetry (like fish) and acquire pentaradial symmetry only in the adult stage — evolutionary evidence that the phylum derives from bilateral ancestors. The 5-fold symmetry aids defense: a predator attacking one side encounters an identical structure on the other, with no weak point.

5. Cite the main characteristics and examples of the 5 classes of echinoderms:
   • Asteroidea
   • Echinoidea
   • Ophiuroidea
   • Holothuroidea
   • Crinoidea

   Answer: There are 5 classes: 1) Asteroidea — starfish (5 or more arms, predators, e.g., red starfish); 2) Echinoidea — sea urchins and sand dollars (a globular or flattened body covered with spines, herbivores/scrapers); 3) Ophiuroidea — brittle stars (a central disk with long, thin, flexible arms, very agile); 4) Holothuroidea — sea cucumbers (a soft cylindrical body, without arms, deposit feeders that turn over the sediment); 5) Crinoidea — sea lilies and feather stars (feather-shaped branched arms, filter feeders, some fixed by a stalk). — Each class has ~1,500-2,000 species. Asteroidea has the greatest colorful diversity; Echinoidea includes edible urchins (sushi); Ophiuroidea are the most mobile; Holothuroidea (cucumbers) are Asian delicacies at US$30/kg; Crinoidea are the oldest (480 million years), known as 'living fossils.'

6. What should you do in case of an accident with sea urchins?

   Answer: You wash the area with soap and water, remove the visible spines with tweezers (pulling perpendicular to the skin), apply vinegar on tropical urchins to neutralize the venom, keep the area clean, and seek medical care if there is intense pain, infection, or deep spines that cannot be removed at home. — Sea urchin spines are brittle and can fragment inside the skin. Vinegar dissolves the calcite of the spines in some tropical species. Species such as the flower urchin (Toxopneustes pileolus) are venomous and require a hospital — their venom can cause severe muscle paralysis.

7. In a practical class, identify, diagram, and explain the function of the following structures:
   • In starfish:
   • In sea urchins:

   Answer: In starfish you identify: the madreporite (the water intake of the water vascular system), the tube feet (locomotion and feeding), the central mouth (on the oral surface), the gonads (reproduction). In sea urchins: the Aristotle's lantern (a chewing apparatus with 5 teeth), the spines (defense), the tube feet, the anus (aboral surface, on top). — The 'Aristotle's lantern' was described by the Greek philosopher in 350 BC — it is the most complex chewing apparatus among invertebrates, with 40 movable pieces. The madreporite is unique to the phylum: it filters seawater to feed the hydraulic system that moves the animal's tube feet.

8. Make a collection containing 20 images or pictures of different species, including in the identification the division into the correct classes.

   Answer: You organize 20 images into 5 classes: Asteroidea (red starfish, sunflower star, etc.), Echinoidea (common sea urchin, tropical sea urchin), Ophiuroidea (common brittle star, tropical brittle star), Holothuroidea (beach sea cucumber, deep-sea cucumber), Crinoidea (tropical and abyssal sea lily). — Use reliable sites (FishBase, WoRMS, the English Wikipedia) for scientific sources. The photo should show distinctive features — for Asteroidea highlight the 5 arms; for Crinoidea, the stalk. Present it in a digital or printed album, with a clear caption on each specimen for the instructor to evaluate.

9. How do starfish feed?

   Answer: You explain that starfish have a unique way: upon finding prey (mussel, oyster, clams), they wrap around it with their arms, open the shell by forcing it with the tube feet, and eject the stomach out of the body (stomach eversion) — they digest the prey outside the body and then retract the stomach back into the cavity. — This mechanism allows them to digest prey larger than their mouth. The digestive acid works outside the body. Some species can evert the stomach in just 60 seconds — an evolutionary adaptation unique in the animal kingdom. Eversion is studied in medicine as a model for tissue regeneration.

10. Conduct research about sea urchins and the venom that some species possess.

    Answer: Some species of sea urchins possess venom, located in two structures: in the globiferous pedicellariae (small pincers with venom glands scattered among the spines) and at the tip of the hollow spines of certain species. Tropical species such as those of the genus Toxopneustes (flower urchin) and Diadema (black urchin with long spines) are the most dangerous, capable of causing intense pain, swelling, numbness, nausea and, in severe cases, breathing difficulty and muscle paralysis. The venom contains substances such as acetylcholine, serotonin, and toxic proteins. The accident occurs by stepping on or touching the animal; treatment involves removing the spines and pedicellariae, washing the area, immersing it in warm water to inactivate the toxin, and seeking medical care. — Pedicellariae are tiny organs between the spines with 3 'jaws' that inject toxin. The venom of Toxopneustes contains peptides that affect the ion channels of muscle cells — an effect similar to some spider toxins. Pharmaceutical research studies these toxins to create potent analgesics.