Invertebrates sponges, segmented worms, echinoderms, mollusks, and arthropods They do not have backbones or internal skeletons.? Some have external skeletons, called exoskeletons ??? Sponges -Very simple animals that have many pores (holes) through which water flows. -Water moves into a central cavity and out through a hole in the top. -obtain their food and eliminate wastes through this passage of water. -They have specialized cells for obtaining food and oxygen from the water. ??? Cnidarians -Hollowed-body animals with cells organized into tissues. -Have tentacles surrounding their mouth that contain stinging cells used to help capture its prey. -Have radial symmetry and two different body forms: polyp and medusa. -Examples are sea anemones, hydra, corals, and sea jellies. ???