Planula

Japanese: planula

…In the Hydrozoa, the gonads arise from the ectoderm on the underside of the radial duct. The fertilized egg becomes a planula with ciliated tissue on the entire surface, which floats and then attaches to the surface to become a polyp. The polyp asexually buds off to form a colony, on which a medusae or sacs are produced, resulting in the sexual generation of jellyfish. …

From [Coelenterates]

...the gonads of hydromedusae are exposed around the mouth stalk or on the inner surface of the umbrella, while in scyphomedusae they are formed in the stomach cavity. The fertilized eggs are cleaved into divisions, equal divisions, radial divisions, etc., and when the endoderm is formed, they become planulae with cilia on the body surface and swim. The planulae eventually attach to the surface and transform into young polyps.

From [Larva]

…Let’s look at the characteristics of each group, starting from the most primitive. (1) Planula Larvae: A larva found only in coelenterates, it has a simple structure in which a cavity surrounded by a wall of ectoderm made of one layer of cells is filled with endoderm cells. It is very similar to the mesoblastula of other animals (Figure 1). …

*Some of the terminology explanations that mention "planula" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…ヒドロ虫綱では生殖巣が放射水管の下側に，外胚葉から生ずる。受精卵から全面に繊毛が生えたプラヌラ幼生planulaになって浮遊し，のち着生してポリプpolypになる。ポリプが無性的に出芽して群体になり，その上にクラゲか子囊をつくって有性世代のクラゲになる。…