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Ptilosarcus undulatus, also known as the fleshy sea pen, is a colonial octocoral that occurs in Atlantic tropical waters from Northern Mexico to Peru. Ptilosarcus undulatus looks like a 16th century scroll pen with a flat central stalk with fleshy lobes. It is typically yellow or orange in color and grows to be 20-30 cm (8-12 inches) (Kerstitch & Bertsch, 2007). Like other octocorals, the colony is comprised of several Autozooids, these are the individual units that are used for feeding and excreting waste. The autozooids in Ptilosarcus undulatus are tubular with hard body covering which contain one, two or eight terminal teeth. There is  one calyx tooth and the siphonozooids are arranged in clumps. These siphonozooids are used to siphon in water so that the autozooids can extract nutrients from the water (Williams, 1995.) The thin tissue of sea pens is called the coenenchyme, and as in all octocorals, is composed of three layers: the outer epidermis and an inner gastrodermis, with a mesogleal layer in the middle. The mesoglea is where the sclerites are formed by specialized amoeboid cells known as scleroblasts (Barnes, 1982). These are the cells that give the sea pen its structure and malleability. Internally, most pennatulaceans have a central axis composed primarily of calcium carbonate called the style, which runs partially or entirely along the length of the animal, and is circular or quadrangular in cross-section. (Williams, 2011). Styles contain concentric growth rings that are assumed to be annual and researchers are able to estimate ages based on the number of rings observed. This technique has proved to be more accurate than measuring individual size to estimate age (Birkeland,1974).


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