. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CUTTLEBONES LIMIT HABITAT DEPTH IN SEPIA 405 septum (Westermann. 1973; Daniel a 1997), or the siplumcle (as reviewed in Jacobs, 1992). If the shell fails catastrophically during implosion, as is the case for Nautilus (Ward ft ul., 1980), empirical tests do not establish the site of initial failure. Thus relative strengths of different parts of the shell must sometimes be calculated theoretically without recourse to direct verification, even in a living animal. Constructing a model of shell strength requires that struc-
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CUTTLEBONES LIMIT HABITAT DEPTH IN SEPIA 405 septum (Westermann. 1973; Daniel a 1997), or the siplumcle (as reviewed in Jacobs, 1992). If the shell fails catastrophically during implosion, as is the case for Nautilus (Ward ft ul., 1980), empirical tests do not establish the site of initial failure. Thus relative strengths of different parts of the shell must sometimes be calculated theoretically without recourse to direct verification, even in a living animal. Constructing a model of shell strength requires that struc- tural geometry, loading conditions, and mode of failure be denned to form the basis for an appropriate model. Even when models are carefully chosen, they are simplifications of complex structures and circumstances. Some simplifica- tions have little effect on strength estimates; others have larger or nonlinear effects that make it difficult to evaluate the reliability of the model's output. Thus it would be informative to evaluate the robustness of a theoretical model on a living cephalopod of known habitat depth to gauge how reliable such estimates are for fossil forms. Habitat depth and morphology vary little among species of Nautilus, and the internally shelled squid Spirilla is monospecin'c. Only one living genus, Sepia, presents a wide range of habitat depths and shell morphologies among its nearly 100 species (Adam and Rees, 1966). Its phragmo- cone, or cuttlebone (Fig. 1), is internal and has a complex microscopic morphology. A method for estimating habitat depth from cuttlebone morphology would improve our a) Length Last septum. Figure 1. (a) Ventral view of the cuttlebone (anterior is to the right) of Sepia papillata. Chambers are emptied through the siphuncular zone, maintaining buoyancy. The last septum is the site of failure due to exces- sive hydrostatic pressure, (b) Microscopic structure of cuttlebone. showing chambers and the undulating, transverse pillars betwe
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
