Abstract. Surveys of the coral-inhabiting snail Coralliophila violacea (Lamarck) (= C. neritoidea Kiener) were made on shallow fringing reefs (< 8 m deep) around Hsiao-Liuchiu, Taiwan, between July and October 1990. The snails were aggregated into patches on the surface of massive poritid coral colonies. Coral colonies > 40 cm in diameter were more likely to bear patches of snails than smaller colonies, and also to have more snails. The coralliophilids ranged from 5 to 30 mm in aperture length. The sex ratio of the population was biased toward males (539:279), with only a few small individuals of indistinguishable sex. Snails between 6 and 10 mm were all males, while most snails with aperture lengths _>20 mm were females. Judging from the distinct size ranges of males and females within patches and from the observed degeneration of the penis, the snails may have changed sex from male to female with increasing size. Sex-change may occur across a wide size range (10 to 20 mm). The correlation of smallest female size and largest male size among patches indicates that snail size at sex-change is peculiar to each individual patch. Those females in patches with a single female (but many males) were significantly smaller than females in multiple-female patches. It is likely that in the absence of females males change sex at a smaller size, whereas in the presence of large females males delay sexchange until they have reached a larger size. The plasticity of size at sex-change may be adaptive and a result of natural selection at the individual level.

This study presents a modified hot-embossing process to fabricate micro-triangular-pyramidal array (MTPA). First, a tungsten (W) steel mold (as the first mold) is manufactured by precision machining including optical projection grinding, lapping, and polishing processes. The dimension of a triangular pyramid with acute angle of 85°on the W-steel mold is about 300 lm in width and 139 lm in height. The pitch between two triangular-pyramidal tips is about 170 lm. Then, only the portion of the tip area of the triangular-pyramidal patterns is transferred on bulk metallic glass (BMG, Mg 58 Cu 31 Y 11 ) using this modified multi-step hot-embossing method to reduce the pattern size. With a position-adjustable mechanism, size-reduced concaved-shaped MTPA can be selectively formed, used as the secondary mold. In this way, not only can the size of triangular-pyramidal patterns on W-steel mold be reduced down on BMG, but also the tool arc between each triangular-pyramid on W-steel mold caused by machine tool can be eliminated. This is based on the fact that amorphous glass alloys contain no dislocation that can be responsible for yielding in crystalline materials. Thus, BMG is expected to be strong and hard enough to be used as a mold material. Then the secondary mold is used to emboss convex-shaped MTPA on PolymethylMethacrylate (PMMA) optical film. Experiments with different embossing times and embossing pressures are conducted and discussed. Large-sized triangular-pyramidal array on the W-steel mold has been successfully and selectively miniaturized on BMG, and then transferred on PMMA. Finally, this optical film of PMMA with MTPA is packaged on light-emitting diode (LED) to improve its lighting uniformity and luminance. In comparison with commercial 3M Ô optical film (3M Ô Vikuiti Ô TBEF2-T-65i), the film with MTPA shows a good optical performance.