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19. Echinodermata only contains five different classes of animals:
Starfish: Starfish, or sea stars, are the classic starfish that most people think of. They have five arts, of varying thickness, and can come in a variety of colors and textures.Brittle Stars: Brittlestars, sometimes called serpent stars, look like typical starfish except their legs are much skinnier and more fragile (hence the brittle in their name). They also feature more prominent spines than the sea stars.Echinoids: The technical name for sand dollars, sea urchins and heart urchins is echinoid. Unlike the sea stars and brittle stars, they contain no arm-like appendages, instead they are shaped like globes or half globes. They are rounded on the top and flat on the bottom, and feature spines of varying length, with sea urchins have longer spines and the sand dollars and heart urchins havingshorter spines.Sea Cucumbers: Sea cucumbers look similar to their namesake, the vegetable cucumber. They have long, cucumber-like bodies, with bumps on the surface of their body.Sea Lilies: The most ancient of the echinoderms, the sea lilies are the lone sessile organisms in the phylum. Fossils of sea lilies are not unusual in regions that used to be located under oceans. All sea lilies have at least ten appendages extending from the main stalk of their body, which they use to feed on detritus.20. The five hallmarks shared by all chordates are the notochord, dorsal tubular nerve cord, pharyngeal pouches or slits, endostyle, and postanal tail. The functions of each of these are..1. Notochord a flexible, rodlike structure, that extends the length of the body. It is the first part ofthe endoskeleton to appear in the embryo. The notochord is an axis for muscle attachment, and because it can bend without shortening, it permits undulatory movements of the body.2. Dorsal Tubular Nerve Cord ventral to the alimentary canal and is solid, but in chordates the single cord is dorsal to the alimentary canal and its a hollow tube. The hollow cord is produced inthe embryo by infolding of ectodermal cells on the dorsal side of the body above the notochord.3. Pharyngeal Pouches and Slits openings that lead from the pharyngeal cavity to the outside. They are formed by inpocketing of the outside ectoderm and evagination, or outpocketing of the endodermal lining of the pharynx.4. Endostyle or Thyroid Gland found in all chordates, but no other animals. The endostyle in the pharyngeal floor, secretes mucus that traps small food particles brought into the pharyngeal cavity.5. Postanal Tail provides the motility that larval tunicates and amphioxus need for their free-swimming existance. It is a structure added to the body behind the end of the digestive tract, and it clearly has evolved specifically for propulsion in water.