The hatching behavior of Echinostoma trivolvis miracidia and their responses to gravity, light and chemicals.

Echinostoma trivolvis eggs developed to mature miracidia in both dark and light culture conditions as early as 7 days. Hatching initially occurred in eggs exposed to incandescent light on day 11. Those exposed to fluorescent light first hatched on day 13. Maximum hatching (50+ miracidia/day) lasted only over a 3-day span with the entire hatching period being at the most 5 days. Eggs stored in complete darkness for 21 days developed to mature miracidia in 9 days, and, when exposed to light, gave a 50+ hatch the next day. Those eggs stored for 28 and 35 days developed normally but never hatched upon exposure to light. Miracidia hatched at all times of the day without a circadian pattern. Miracidia that hatched from these trials exhibited a definite negative geotaxis in a four-tube vertical system. This response was either negated in open tubes or dominated by a positive phototaxis in the open-bottomed tubes. In horizontal chambers without the depth component, a strong positive phototaxis was also demonstrated. Miracidia showed a positive klinokinetic response, as determined in phi-chambers, to acidic compounds such as aspartic, glutamic, hydrochloric, sulfuric, and acetic acids. Snail-conditioned water prepared from Helisoma trivolvis snails also elicited a positive response. The neutral amino acid, leucine, and possible snail excretion products, Mg2+ and ammonia, did not stimulate these echinostroma miracidia.