In a reverse hierarchy, the conceptual pyramid of authority is turned upside-down, so that the apex is at the bottom and the base is at the top. This model represents the idea that members of the higher rankings are responsible for the members of the lower rankings.
Along the sides of the body is a light-colored horizontal stripe called the lateral line. The line is made up of a series of tiny pores that lead to receptors that are sensitive to the mechanical movement of water and sudden changes of pressure.The spiny dogfish has a double dorsal fin.The anterior dorsal fin is larger than the posterior dorsal fin.The spiny dogfish has the presence two spines, one immediately in front of each dorsal fin. The spines carry a poison secreted by glands at their base.he spiny dogfish has a double dorsal fin. The anterior dorsal fin is larger than the posterior dorsal fin. The spiny dogfish has the presence two spines, one immediately in front of each dorsal fin. The spines carry a poison secreted by glands at their base.
These are called tube feet. By varying the internal water pressure, the echinoderm can extend and contract its tube feet for locomotion, food collection and respiration. Characteristic of all echinoderms is the presence of an internal skeleton covered with spines and skin.The skeleton varies with the type of echinoderms. In sea stars and brittle stars, the skeleton consists of multitudes of small calcareous plates called âossiclesâ that move with one another, forming flexible joints.chinoderms are characterized by their radial symmetry, water vascular system and internal skeleton. The most striking feature of all echinoderms is their pentamerous radial symmetry.