Bivalve nacre is a brick-wall-patterned biocomposite of aragonite platelets surrounded by organic matter. SEM-electron back scatter diffraction analysis of nacre of the bivalve family Pteriidae reveals that early aragonite crystals grow with their c-axes oriented perpendicular to the growth surface but have their a-and b-axes disoriented. With the accumulation of successive lamellae, crystals progressively orient themselves with their b-axes mutually parallel and towards the growth direction. We propose that progressive orientation is a result of competition between nacre crystals at the growth front of lamellae, which favours selection of crystals whose fastest growth axis (b-axis) is oriented parallel to the direction of propagation of the lamella. A theoretical model has been developed, which simulates competition of rhombic plates at the lamellar growth front as well as epitaxial growth of crystals onto those of the preceding lamella. The model predicts that disordered nacre progressively produces bivalve-like oriented nacre. As growth fronts become diffuse (as is the common case in bivalves) it takes longer for nacre to become organized. Formation of microdomains of nacre platelets with different orientations is also reproduced. In conclusion, not only the organic matrix component, but also the mineral phase plays an active role in organizing the final microstructure.

Angiotensin converting enzyme (ACE) plays an important role in the pathogenesis of pulmonary hypertension. In this study we determined whether the deletion (D)/insertion (I) polymorphism in the ACE gene may be associated with pulmonary hypertension evoked by exercise challenge in patients with chronic obstructive pulmonary disease (COPD). ACE genotypes were determined in 19 patients with COPD. All patients underwent right heart catheterization followed by a constant-load exercise test while breathing room air or oxygen. Subgroups were created of seven patients with the II genotype, six with the ID genotype, and six with the DD genotype who were well-matched with respect to age, blood gas data at rest or after exercise, baseline lung function, results of incremental exercise testing, and hemodynamic data at rest. The mean pulmonary arterial pressure (Ppa) and pulmonary vascular resistance (Rpv) at rest in the three subgrpoups did not differ significantly during breathing of either room air or oxygen. However, the Ppa after exercise challenge in patients with the DD genotype (55.7 +/- 4.9 mm Hg [mean +/- SD]) was significantly higher than in patients with the II genotype (42.6 +/- 7.1 mm Hg, p = 0.008). The Rpv after exercise in patients with the DD genotype was also significantly higher than in patients with the ID and II genotypes. During breathing of oxygen to diminish acute hypoxic pulmonary vasoconstriction, the Ppa in patients with the DD genotype (52.3 +/- 3.1 mm Hg) was higher than in patients with the ID genotype (40.5 +/- 5.9 mm Hg, p = 0.0049) or the II genotype (37.7 +/- 5.9 mm Hg, p = 0.0027). In addition, the Rpv in patients with the DD genotype was higher than in patients with the ID and II genotypes. These results suggest that D-I polymorphism in the ACE gene may be associated with pulmonary hypertension evoked by exercise challenge in patients with COPD. However, the number of patients in this study was very small for a genetic association study, and our results should be examined in larger studies.

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Arm autotomy was induced in a living specimen of Metacrinus rotundus (Echinodermata: Crinoidea). An arm was autotomized at a ligamentary articulation known as a cryptosyzygy, following incision by scissors distal to the break point. Although sessile stalked crinoids cannot entirely escape from a predatory attack by arm autotomy and they do not have an active defense, arm autotomy at cryptosyzygies reduces damage and arm loss by effective distribution, and by minimizing trauma and facilitating subsequent regeneration.The paradigmatic distribution of cryptosyzygies in which arm loss is set at a minimum, compared with the actual distribution, shows that these two patterns are similar and that actual specimens successfully reduce arm loss by the effective distribution of cryptosyzygies. The crinoid branching pattern also affects arm loss, and two different paradigms are discussed: anti-predatory and harvesting. Arm branching patterns of various isocrinids have tended toward the anti-predatory configuration from the Jurassic to the Recent, suggesting that the isocrinids have coped with increased predation. Shallow-water comatulids generally adopt the anti-predatory paradigm in their branching pattern, whereas many deep-water, stalked crinoids adopt a harvesting paradigm, reflecting that shallow-water comatulids receive more predatory attacks than do deep-water crinoids.

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Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.

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