ELLERBY, D.J.*; MARSH, R.L.; CARR, J.A.: Gill muscle function in the horseshoe crab Limulus polyphemus
Gas exchange in Limulus is carried out via five paired gill plates on the underside of the opisthosoma. During ventilation, slow rhythmical movements of the gill plates induce water flow through the gill lamellae. Rapid, high amplitude movements of the gills produce thrust during swimming. Sonomicrometry and electromyography were used to obtain strain and activity records from the principal gill remotor muscle of the first gill pair. The frequency of the gill movement cycle at 14 °C ranged from 0.25 Hz during ventilation to 0.75 Hz during swimming. Strain patterns were approximately sinusoidal. Maximum muscle strains were 8% L0 during ventilation and 14% L0 during swimming, where L0 is the minimum muscle length during cyclical gill movements. The work loop technique was used in vitro to determine the work and power outputs of the gill remotor muscle under simulated ventilatory and swimming movements. The phases of EMG activity recorded in vivo were similar to the stimulus phases that yielded maximum work in vitro. This work was supported by NIH grant AR 47337.
