LIVING MATERIAL

The colony consists of solitary brick-red hydroids branching from a filiform hydrorhiza. The polyps are about two cm. high, and have approximately 20 filiform tentacles arranged irregularly about a long hypostome. See the diagram by Hyman (1940).

The colonies are found in shallow water, attached to fronds of rock-weed (Fucus nodosus).

A. Care of adults: The colonies should be kept in large dishes, supplied with sea water.

B. Methods of Observation: All stages of development up to the mature planulae can be teased from the female gonophores with fine needles. Larvae, released from ripe colonies, should be pipetted to fingerbowls of fresh sea water. They will then attach and metamorphose.

Normal Development

A Asexual Reproduction: The gonophores develop in dense, bud-like clusters just below the tentacles. Those of the male colonies are pink, those of the female colonies purple. In both sexes they are very degenerate, retaining few traces of the medusa structure. Although there are only a few eggs present in each of the female gonophores, there is no evidence of a phagocytosis of nurse cells. Details of gonophore development are available in the papers by Harm (1902) and Kuhn ( 1910).

B. Sexual Reproduction: The large eggs (131 microns in diameter, according to Hargitt, 1919) possess a delicate blue pigment, which appears during maturation and increases and spreads during the cleavage process. Fertilization is internal, and regular or irregular cleavage leads to the formation of a solid morula. The endoderm is formed by a secondary delamination within this mass (Harm, 1902). The oval embryo then elongates, becomes ciliated, and acquires the beginning of the coelenteron. At this stage, the planulae burst from the gonophores.

C. Later Stages of Development and Metamorphosis: The free-swimming planula creeps about for some time, exhibiting marked muscular contractions. Gland cells and nematocysts develop in the ectoderm, and the coelenteron increases in size. Eventually the larva becomes fixed at its broad anterior end, loses its cilia, and flattens out somewhat. It then elongates in the direction of the main body axis, and the first tentacles appear at the free end; this produces a functional hydroid. See the paper by Harm (1902), for further details.

HARM, K., 1902. Die Entwicklungsgeschichte von Clava squamata. Zeifschr. f. wiss. Zool., 73: 115-166.

HARGITT, C. W., 1906. The organization and early development of Clava leptostyla Ag. Biol. Bull., 10: 207-232.

HARGITT, C. W., 1911. Some problems of coelenterate ontogeny. J. Morph., 22: 493-549.

HARGITT G. T., 1916. Germ cells of coelenterates. II. Clava leptostyla. J. Morph., 27: 85-97.

HARGITT, G. T., 1919. Germ cells of coelenterates. VI. General considerations, discussion, conclusions. J. Morph., 33: 1-60.

HYMAN, L. H., 1940. The Invertebrates: Protozoa through Ctenophora. McGraw-Hill Book Co., New York.

KEMP N. E., 1952. Regeneration in isolated and fused pieces of Clava leptostyla. Biol. Bull., 102: 141-148.

Kühn A., 1910. Die Entwicklung der Geschlechtsindividuen der Hydromedusen. Zool. Jahr. abt. Anat. u. Ontog. der Tiere, 30: 43-174.