. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 1. Stiffness measuring technique, a double exposure. The spicule was moved to contact and bend the stationary needle, and the first exposure was taken. Then the spicule was moved free of the needle, and a second exposure was taken. The image of the undeflected spicule was then drawn onto the photo. Dimensions were taken from the photographs. Black lines show the length of the cantilever needle, Ln, and spicule, Ls. Yn and Ys are the distances of deflection of the needle and spicule respectively. See text for further e

. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 1. Stiffness measuring technique, a double exposure. The spicule was moved to contact and bend the stationary needle, and the first exposure was taken. Then the spicule was moved free of the needle, and a second exposure was taken. The image of the undeflected spicule was then drawn onto the photo. Dimensions were taken from the photographs. Black lines show the length of the cantilever needle, Ln, and spicule, Ls. Yn and Ys are the distances of deflection of the needle and spicule respectively. See text for further e Stock Photo
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RHN4H5

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. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 1. Stiffness measuring technique, a double exposure. The spicule was moved to contact and bend the stationary needle, and the first exposure was taken. Then the spicule was moved free of the needle, and a second exposure was taken. The image of the undeflected spicule was then drawn onto the photo. Dimensions were taken from the photographs. Black lines show the length of the cantilever needle, Ln, and spicule, Ls. Yn and Ys are the distances of deflection of the needle and spicule respectively. See text for further explanation. Scale (white line): 0.1 mm. This equation can be rewritten in the following way: EsIs = (Yn/Ys).(Ls/Ln)3-(EnIn) Only bends where Yn/Ln and Ys/Ls ;S 10% were used because this equation is not accurate for larger deflections where shear in the material becomes increasingly important (Faupel, 1964). No attempt was made to measure breaking strength. For simple spicules which are circular in cross-section, / =: 1/4 ?rr4 with r = ra- dius of the spicule. For the fenestrated spicules, / :: 3/4 Trr4 + 3/2 vrrd2, with r = radius of the element rods and d == radius of the spicule. The amount (volume) of skeletal material in larval spicules was also estimated with dimensions taken from SEM photos. I treat the fenestrated spicules as three parallel circular cylinders joined by cross-ties. Other mechanical calculations will be introduced as needed in the discussion. They are taken from Wainwright et al. (1976) and Faupel (1964), and may be found in most general mechanical engineering texts. RESULTS The spicules of echinoplutei reared during this study are 500 to 800 ^m long. Simple spicules range in diameter from 2 to 4 ^m. Each of the three elements of fenestrated spicules are 1.5 to 2.5 nm in diameter and the whole spicule is 5 to 10 /j.m in diameter (Fig. 2). Fenestrated spicules contain about twice as much material as simple ones of similar length. In a fenestrated spicule t

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