ON MEDUSA-BUDDING IN THE ANTHOMEDUSA, PODOCORYNE MINIMA (TRINCI)

Abstract

With Text-figures 1-2 In 1928 Kramp described a new hydromedusa from Japan under the name of Podocoryne simplex and later Uchida (1930, 1938, 1947 and 1964) recorded the same medusa from several localities of the Pacific. While studying a lot of specimens of this medusa, however, the writers came to the conclusion that Podocoryne simplex is nothing but a synonym of Podocoryne minima (Trinci, 1903) as was pointed out already by Russell (1954). Podocoryne minima is widely distributed along the coasts of Japan but the materials here dealt with were mostly collected at Misaki, Kanagawa Prefecture from 1971 to 1976. In addition, some specimens from Amakusa, Kumamoto Prefecture were also examined. As little has been reported on medusa-budding in this species, the details of the observation made by the writers will be given in the present paper. Morphological Features of Medusa The medusa is very small, the height and width of the umbrella are almost equal and 0.3 to 0.9 mm. The umbrella is globular, but somewhat narrowed and elevated in the upper part. The jelly is rather soft and thin. The four radial canals are distinct and straight, while the ring canal is narrow and indistinct. The marginal tentacles are each prolonged from the oval tentacle bulb and fundamentally four in number, though tending to decrease their number and length. Frequently some of them are missing or ill-developed. They are liable to contract but sometimes are extended over several times the diameter of the umbrella. When fully extended, nematocyst clusters can be obviously seen as transverse stripes on the tentacle shaft but its basal part. The velum is well-developed and squarish, because the ring canal runs straight between the perradial tentacle bulbs. When the velum is spread extensively, only a small aperture is left at the center under the umbrella. The manubrium bearing medusa-buds and terminating in four oral tentacles, each with-out further branching and ending in a spiny cluster of nematocysts, IS extensile Publ. Seto Mar. Bioi. Lab., XXIV (1/3), 53-57, 1977.