title   hydra oligactis: before, after,
hydra hungry spacer hydra grown
subtitle:  and how it got that way

hydra catches daphnia hydra engulfs daphnia hydra digests daphnia
Drawn to scale with one another, these images tell everything but the time. "Before" was 5:00 p.m. of the day after I'd brought the hydra home, examined it, and put it in a jar of water well populated by water fleas. "After" was midnight, only seven hours later. The hydra caught the daphnid at 5:20. By 5:25 the hydra's mouth had expanded noticeably, covering about half of one side of the prey's carapace. By 5:40 the hydra's mouth had closed, and the hydra's body sagged downward with the weight of its meal. When I checked at 10 o'clock, the hydra's position and appearance had not changed. At midnight, I found a noticeably larger hydra; its bud and the bud's tentacles had grown, too. 

The brown hydra, H. oligactis, is the largest of the common hydrozoans. It is said that this species sometimes causes problems at fish hatcheries by eating the small fry. You'd better believe it. 

Comments to the author Comments to the author sent via our contacts page quoting page url plus : ('rarbur','')">Rosemarie Arbur welcome.


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