Meeting Abstract
P3.34 Tuesday, Jan. 6 An Investigation of the Mechanics of Ventilation and Sliming in Pteraster tesselatus CROFTS, S.C.*; GOSLINE, J.; Univ. of California, Irvine; Univ. of British Columbia scrofts@uci.edu
While the body of Pteraster tesselatus is similar to other sea stars, it is also covered by a supradorsal membrane. The resulting space, the nidamental cavity, can inflate with water and deflate, allowing the sea star to actively ventilate as well as release a defensive slime. Water is pulled into the nidamental cavity through ambulacral pores, located at the junction between the supradorsal membrane and the body wall. During ventilation, water is expelled through an opening at the top of the supradorsal membrane, the osculum. During sliming, water and mucus are expelled through spiracles in the supradorsal membrane, rather than the osculum. The goal of this study was to better understand this water pumping system and to identify differences between the two behaviors. Change in volume and pressure changes in the nidamental cavity were measured for different sized individuals displaying both behaviors to quantify the water pumping mechanism and identify any variations with size. Histological sections were used to illustrate the morphology and mechanisms that allow for the change in volume. Change in volume scales geometrically during ventilation, whereas changes in volume during sliming appear to be allometric. Pressure traces indicate that during the inflation phase of ventilation, pressure in the nidamental cavity of both individuals measured was approximately -0.5 cm H2O. During deflation there was a sharp peak of positive pressure, approximately 2.5 cm H2O in the larger individual and approximately 1.5 cm H2O in the smaller individual. During sliming, pressure traces became more sinusoidal and a wider range of pressures was achieved; ranging from -1.5 to 2 cm H2O in the large individual and from -0.5 to approximately 1 cm H2O in the smaller individual. Histology illustrates the muscles and connective tissue that allows for these changes in pressure.
