may also have venom glands, photophores, or cells that produce a more watery serous fluid in the dermis. Scales Also part of the fish's integumentary system are the scales that cover the outer body of many jawed fish. The commonly known scales are the ones that originate from the dermis or mesoderm, and may be similar in structure to teeth. Some species are covered by scutes instead. Others may have no scales covering the outer body. There are four principal types of fish scales that originate from the dermis. Placoid scales, also called dermal denticles, are pointed scales. They are similar to the structure of teeth, in which they are made of dentin and covered by enamel. They are typical of cartilaginous fish (even though chimaeras have it on claspers only). Ganoid scales are flat, basal-looking scales. Derived from placoid scales, they have a thick coat of enamel, but without the underlying layer of dentin. These scales cover the fish's body with little overlapping. They are typical of gar and bichirs. Cycloid scales are small, oval-shaped scales with growth rings like the rings of a tree. They lack enamel, dentin, and a vascular bone layer. Bowfin and remora have cycloid scales. Ctenoid scales are similar to cycloid scales, also having growth rings, lack enamel, dentin, and a vascular bone layer. They are distinguished by spines or projections along one edge. Halibut have this type of scale. Another less common type of scale is the scute, which may be an external, shield-like bony plate; a modified, thickened scale that is often keeled or spiny; or a projecting, modified (rough and strongly ridged) scale. Scutes are usually associated with the lateral line, but may be found on the caudal peduncle (where they form caudal keels) or along the ventral profile. Some fish, such as pineconefish, are completely or partially covered in scutes. Their function are intended for protection as a body armor for fish against environmental abrasions and predations from other species. Lateral line The lateral line is a sense organ used to detect movement and vibration in the surrounding water. For example, fish can use their lateral line system to follow the vortices produced by fleeing prey. In most species, it consists of a line of receptors running along each side of the fish. Photophores Photophores are light-emitting organs which appear as luminous spots on some fishes. The light can be