EFFECTS OF HIGH-TEMPERATURE ON LARVAL DEVELOPMENT AND METAMORPHOSIS OF ARACHNOIDES-PLACENTA (ECHINODERMATA, ECHINOIDEA)

Adults of the sea urchin Arachnoides placenta (L.) were induced to spawn, and eggs were fertilized at 28-degrees-C in September 1989. After 5 min, eggs were transferred to 28, 31, 34, or 37-degrees-C and reared to metamorphosis. Embryos were observed at 20-min intervals during the first 2 h; larvae were observed daily. The cleavage was higher at higher temperatures. Embryos reared at 28-degrees-C were still at the 4th cleavage (16-cell stage) after 100 min, while those at 34-degrees-C had reached the 5th cleavage (32-cell stage). All embryos reared at 37-degrees-C died on the second day. Incidence of abnormality was 20 to 30% at 28 and 31-degrees-C, 48% at 34-degrees-C, and 77% at 37-degrees-C. The 8-arm stage was reached after 4 d at 28-degrees-C, 3 d at 31-degrees-C and 2 d at 34-degrees-C. Larvae displayed decreasing body length and arm length with increasing temperature. Larvae at 31-degrees-C have relatively long arms, as a result of a decrease in body length, not because of increased arm length. Incidence of metamorphosis was 43.9 +/- 1.7% (mean/plusmn;SD) at 28-degrees-C, 24.5 +/- 1.9% at 31-degrees-C, and 5.3% at 34-degrees-C. The size of metamorphosed juveniles was significantly larger at 28-degrees-C than at 31 and 34-degrees-C. Temperatures of greater-than-or-equal-to 31-degrees-C negatively affect larvae and juveniles of the sand dollar.