Larval recruitment is influenced by intrinsic biological traits (e.g. swimming behavior) and environmental factors. In this study, I examined the effects of environmental factors (e.g. light, temperature, salinity and pH) on the development of an intertidal keratose sponge from Peng-hu. The experiments included species identification, the observation of larval development, effects of environmental factors on larval choice and development. Based on morphological characters and the mitochondrial COI (cytochrome c oxidase subunit I) gene, the sponge is identified as Spongia ceylonensis which is viviparous. Sponge larva is a typical lecithotrophic, tufted parenchymella, about 500 £gm long and ovoid in shape. The mean swimming speed was 3.9 ¡Ó 0.6 sec/cm. Under natural light condition (3500 ¡V 6500 lux), planktonic stage was 5-6 hours. In the vertical dark/light choice experiments, larvae exhibited a negative phototaxis with larvae distributed in dark areas in all treatments except the light-treated group. A significant shorter time period for metamorphosis in the light-treated group than all other groups (all dark, upper-half dark and lower-half dark) (p < 0.0001) had been observed. Under various light gradients of single light source, i.e. fluorescent, non-UV, UVA, UVB or UVC light, larvae preferred in the darkest area. Under various light sources (fluorescent, non-UV, UVA, UVB and UVC lights) with the same intensity (220 ¡Ó 10 lux), there was no significant differences (p > 0.05) in the distribution of larvae. In all, larvae had strong dark preference and no preference on different light sources. Under various environmental gradients of each experimental factor (i.e. pH 6.5 ¡V 9.0; temperature: 20 ¡V 40¢J; silica: 0.5 ¡V 20.5 mg/L) in all light or all dark conditions, larvae showed no significant preference (p > 0.05). In salinities of 5, 15, 25 and 45 psu, some larvae had abnormal development as ball formation or dead. At pH 8.0 and 8.2, sponge juveniles developed better than the groups of pH 7.0¡B7.5¡B8.5 and 9.0. In addition, there was no significant difference in larval development (p > 0.05) under various silica concentrations (i.e. SiO2 0¡B2.5¡B5.0¡B7.5¡B10.0 mg/L).