Notes on the biology ofProtohydra leuckartigreef (Hydroidea, protohydridae)

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Abstract
The solitary polyp Protohydra leuckarti Greef is extremely common in Danish estuaries and lagoons. It may be found on several kinds of substratum but seems to prefer mixed bottom in shallow water. P. leuckarti is normally red due to carotenoids from devoured copepods. Experiments showed that the polyp is able to catch all stages of harpacticoids, nematodes and small chironornids, Halacarids and ostracods were not readily accepted and hardly play any role as food animals in nature. The transversal division is the normal way of reproduction. The process lasts 12–24 hours at 20° C and about nine days at 4–5° C. Fed with one adult harpacticoid (Tachidius sp.) per day P. leuckarti would divide every four days. Protohydra seems to have a resting period in the autumn. Sexual reproduction was found in autumn animals and in some winter animals casually exposed to drastically changing temperatures and periods of starvation. The ripening of the gonads lasted 28 days. The eggs measured 310 × 160 µ. They were expelled but did not develop. The mother animals do not die after spawning, but in some cases they perform abnormal divisions, and it seems probable that a report on budding in this species is due to a misinterpretation of this phenomenon.

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