A. The class Asteroidea contains sea stars. They live on hard substrates in marine environments. Some species also live in sandy or muddy substrates. Sea stars feed on snails, bivalves, crustaceans, polychaetes, corals, and detritus. Some sea stars ingest whole prey. These are predators. The preys indigested extracellularly within the stomach. Undigested material is expelled through the mouth. Gases, nutrients, and metabolic wastes are transported to the coelom by diffusion and ciliated cells. Gas exchange and excretion occur by diffusion. Most sensory receptors are distributed over the surface of the body and tube feet. Seastar shows the response to light, chemicals, and various mechanical stimuli. They have specialized photoreceptors at the tips of their arms. These are actually tube feet that lack suction cups. They use tube feet on their arms to help them move, and each tube foot contains what is called an ampulla. These ampulla move water into the tube feet to help stretch them.
B. Ophiuroids are a large group of echinoderms that includes the brittle stars (Ophiurida) and basket stars (Euryalida). Ophiuroids are common in many shallow-water marine habitats and include a few species which can adapt to brackish water, which is quite unusual for echinoderms. Ophiuroids are dominant in many parts of the deep sea, wherein certain regions the bottom may swarm with brittle stars. Basket stars also tend to live in deeper water. These are predators. Ophiuroids are carnivores, filter feeders, and scavengers; those of some species use more than one method to obtain food. Gas exchange and excretion occur through cilia-lined sacs called bursae; each opens onto the interambulacral area of the oral surface of the disc, and typically there are 10 per animal. A radial canal extends into each arm from the ring canal, and lateral canals from each radial canal supply the tube feet. The tube feet of ophiuroids lack suckers and ampullae.
C. The class Echinoidea contains sea urchins, sand dollars and heart urchins. Most of the sea urchins live on wave-exposed rocks, and on coral reefs. Sand dollars live in sand and coarse gravel. Echinoids have a hard calcareous shell made up of a skeleton of tightly packed or fused plates They eat algae, seagrass, and seaweed. The tube feet are part of the urchin's water vascular system. They work like a hydraulic system. The urchin contracts its muscles to push water into the tube feet. Tube feet can also act as respiratory organs and are the primary sites of gas exchange in heart urchins and sand dollars, both of which lack gills. To protect themselves from predators, sea urchins will react immediately if something sharp touches their shell and they will point all of their spines towards the area being poked. They are also light-sensitive.
D. The holothuroideans, commonly called sea cucumbers, are a very unique group of echinoderms. Tube feet can be found all over the holothuroidean's body that is usually contracted within the external body wall. Holothuroidea is generally scavengers, feeding on debris in the benthic zone of the ocean. Some sea cucumbers position themselves in currents and catch food that flows by with their open tentacles. The animal pumps water into the respiratory trees by contracting the cloaca, and oxygen diffuses through from the walls of the trees into the fluid of the body cavity. When threatened, some sea cucumbers discharge sticky threads to ensnare their enemies. Others can mutilate their own bodies as a defense mechanism.
Phylum Echinodermata Answer these questions. a.Class Asteroidea---name animals, describe shape, habitat, type of feeding--(deposit, grazer, predator),...