The Wet World of Sponges - Anatomy - Structure and Spicules



The Exterior Layer \| The Interior Layer \| Different Grades \| Structure and Spicules \| Home
	Spicules and Skeleton Tiny, pointing spicules Cover the sponges of the sea Serving so many purposes Besides looking rather bristly Essentially, spicules are the skeletons of porifera. With multitudes of spicules covering an average porifera, these needle-like projections facilitate the purposes of protection and preservation. If spicules did not exist, not only would sponges not possess a fossil record, but they would be more susceptible to consumption by superior animals. Not to mention, they would have no structure at all. In order to be a sufficient skeleton, spicules, extending from the interior to the exterior, beyond the pinacocytes, need to be of a durable composition. These fierce bristles also leave predators with a rather spiny problem. Spicules are composed of an array of substances. The following are more prominent: • Silica- Silica crystals can produce rather sharp spicules. However, in a chlorine and bleach solution, and with other materials affecting their composition, these spicules can actually dissolve. Such is only observed with demosponges. Despite this, silica spicules are extremely sturdy. • Calcium carbonate-Such spicules are theorized to only be characteristic of the calcareous porifera, hence the name. It is extremely hard and durable, so calcareous sponges form a more developed fossil history. This material is also evident within pearls. A pearl is formed when a grain of sand or other foreign object ends up in the interior of an oyster. To end the irritation, the oyster secretes a liquid of calcium carbonate. Slowly, layer upon layer, a pearl is generated. • Spongin- This is probably the most obvious of all the materials when it comes to definition. Spongin in a fine fiber which circulates water with facility. Usually, it is not found in nature as a single constituent of spicules. Instead, it may be a component of the inner layers of a spicule. Compounded forms of spongin and silica are common substances in demosponge spicules. Not only are spicules practical for defense against predators, but when they are microscopically viewed, they glisten and shine with an array of light. Silica spicules have earned hexactinellids the name of glass sponges.