Explain how body plan and anatomy enables a sea urchin to perform
the essential functions it needs to survive.
Explain how a sea urchin fits into the cladogram of invertebrates.
To understand how the body plan and anatomy of a sea urchin enable it to perform essential functions for survival, we can examine its key features.
1. Symmetrical Body Plan: Sea urchins exhibit a radial symmetry, with their body parts arranged symmetrically around a central axis. This allows them to efficiently navigate and respond to stimuli from all directions. Their spherical shape helps protect their delicate internal organs.
2. Exoskeleton: Sea urchins have a hard exoskeleton composed of calcium carbonate plates called "tests." This rigid structure provides protection against predators and physical damage, allowing them to survive in harsh environments.
3. Spines: Sea urchins have sharp spines extending from their bodies. These spines serve multiple purposes like defense, locomotion, and maintaining equilibrium. They can use their spines to deter predators and create a sturdy grip on surfaces, enabling them to move or anchor themselves as needed.
4. Water Vascular System (WVS): Sea urchins possess a unique hydraulic system called the water vascular system. This system consists of a series of canals filled with seawater, connected to tube feet located on their undersides. The tube feet play a vital role in feeding, locomotion, and respiration. By pumping water into the tube feet, sea urchins can extend or retract them, allowing precise movement and the capture of food particles.
5. Digestive System: Sea urchins have a specialized mouth structure called Aristotle's lantern. It consists of five calcified teeth used for scraping algae and other plant material off surfaces. The mouth leads to a complex digestive system, allowing efficient digestion and absorption of nutrients.
Now, let's discuss how a sea urchin fits into the cladogram of invertebrates.
Cladistics aims to determine evolutionary relationships based on shared characteristics. A cladogram is a branching diagram that represents these relationships. Sea urchins belong to the phylum Echinodermata, which is part of the deuterostome lineage in the animal kingdom. Echinoderms include sea stars, sea cucumbers, and sea lilies, among others.
At a broader level, invertebrates can be divided into several phyla, including Porifera (sponges), Cnidaria (jellyfish, corals), and Arthropoda (insects, crustaceans). Sea urchins are not directly related to these phyla, as they belong to the phylum Echinodermata, which evolved separately from these other groups.
Within the phylum Echinodermata, sea urchins belong to the class Echinoidea. This class comprises sea urchins and sand dollars, which share common traits such as a spherical or disc-shaped body, a hard exoskeleton, and tube feet. Sea urchins are further classified into families, genera, and species based on specific anatomical and genetic characteristics.
In summary, sea urchins possess specialized body features and anatomy, such as their symmetrical body plan, exoskeleton, spines, water vascular system, and digestive system, which enable them to survive in their marine habitats. Additionally, they fit into the cladogram of invertebrates as part of the phylum Echinodermata and the class Echinoidea.