This genus is very similar to Hydractinia. The colony is composed of an encrusting mat of stolons covered with a perisarc which is beset with jagged spines. From these hydrorhizae arise the feeding polyps, each having a single whorl of tentacles around a conical proboscis; the slender protective hydranths lack tentacles but are armed with batteries of nematocysts. The reproductive hydranths bear clusters of gonophores just below the tentacles. For a further description, see the paper of Hargitt (1901).

The species is rare at Woods Hole, Mass.; it is occasionally collected with colonies of Hydractinia from Sheep Pen Harbor. Like the latter species, it is found as an encrusting mat on snail shells, but the ratio of Hydractinia to Podocoryne colonies is about 100 to 1.

A. Care of Adults: The colonies should be maintained in adequate supplies of sea water

B. Methods of Observation: If ripe colonies are isolated in fingerbowls of sea water, the medusae are often discharged. Stages of medusa development can be obtained by dissection from the gonophores.

A. Asexual Reproduction: A single medusa develops within each gonophore, and only male or female medusae are produced by any one colony. The details of medusa development are described by Goette (1907). When they are fully formed, the nearly perfect medusae escape into the water. At the time of release, they have a marked bell-shape, a definite velum, and a short, reduced manubrium. At the end of the four radial canals can be seen four marginal tentacles, and between these there are four interracial tentacles. Although some strains of this species have mature gonads at the time when they are set free, the strain available at Woods Hole has only very immature gonads visible along the radial canals. Goette (1916) states that the medusae may give rise to several additional generations of medusae by budding before they produce gametes. Diagrams of the medusae are available in the paper by Hargitt (1901).

B. Sexual Reproduction: This phase of the life history has been studied by de Varenne (1882), in one of the strains having a free-swimming life of only a few hours. Fertilization is external and occurs before the breakdown of the germinal vesicle. The egg is said to exhibit marked amoeboid movements. Total cleavages lead to the formation of a solid, oval morula; an internal cavity soon appears and the elongating, ciliated larva quickly develops into a free-swimming planula. After a few hours the planula loses its cilia, fixes by its anterior end, and secretes a perisarc. The free end develops the mouth and tentacles of a typical hydroid.

BERRILL, N. J., 1953. Growth and form in gymnoblastic hydroids. VI. Polymorphism within the Hydractiniidae. J. Morph., 92: 241-272.

BUNTING, M., 1894. The origin of the sex cells in Hydractinia and Podocoryne; and the development of Hydractinia. J. Morph., 9: 203-236.

GOETTE, A., 1907. Vergleichende Entwicklungsgeschichte der Geschlechtsindividuen der Hydropolypen. Zeitschr. f. wiss. Zool., 87: 1-336.

GOETTE, A., 1916. Die Gattungen Podocoryne, Stylactis und Hydractinia. Zool. Jahr. abt. Syst., Geog., Okol. Tiere, 39: 443-510.

HARGITT, C. W., 1901. Synopses of North-American Invertebrates. XIV. The Hydromedusae. Amer. Nat., 35: 301-315, 379-395, 575-595.

MAYER, A. G., 1910. Medusae of the world. I and II. The Hydromedusae. Carnegie Inst. Wash. Pub. 109.

DE VARENNE, M. A., 1882. Developpement de l'oeuf de la Podocoryne carnea. C. R. Acad. Sci., 94: 892-894.