Hashimoto, H., 1985. Medusa of fresh-water hydroid, Astrohydra japonica Hashimoto. Zool. Sci. 2 5: 761-766.

24474

Hashimoto, H.

1985

2: 761-766

Publication

Astrophydra is a minute fresh-water hydroid described from Japan, 1981. The polyp produces asexually by giving off the frustule as in Microhydra, but the sexual reproduction has not been found. In 1984, unexpectedly medusae appeared from Astrohydra reared in the laboratory. The medusa bud of Astrohydra is lacking in a basal stem which is normally seen in Microhydra, so the medusa of Astrohydra is directly released from the lateral of polyp body. The newly released medusae are only 0.5 mm in diameter and hemispherical in shape, with four long perradial and four short interradial tentacles. The tentacles of this medusa bear many bristle-like papillae with one to two nematocysts on apices. A papilla consists of only a vacuolate single cell and sometimes reduces to a short process especially when the tentacle is contracted. The radial canals are mostly four in number and the manubrium forms a quadrangular prism, of which basal portion holds the stomach. The oral part bears four small lips. The statocysts are devoid of tubular appendages. One medusa survived for 28 days after liberation and grew to a diameter of 1.35 mm with 29 tentacles and 15 statocysts, but the gonads were not formed. Descriptors: MICROHYDRA figs. 1-6. (x.1985).

Cycles, Saisonality, Phenology

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