These colonial bryozoans are moderately common on shells and algae in shallow water. The zoids arise independently from a branched, creeping stolon, and have cup-shaped calyces and yellow-red stalks. Hyman (1951) reports that Pedicellina is sometimes hermaphroditic, sometimes dioecious.

Although this has not been determined for the Woods Hole, Mass., region, it probably occurs during the summer months.

A. Care of Adults: The animals are moderately hardy in the laboratory, if they are supplied with running sea water.

B. Methods of Observation: Cleaving eggs and young larvae can be dissected from the egg capsules; older larvae will be released if fertile colonies are allowed to stand in fingerbowls of fresh sea water. Harmer (1887) states that the larvae will not attach in small amounts of water. He suggests placing the ripe colonies, together with the algae to which the colonies are attached, in glass jars covered with fine bolting silk. These jars are then suspended in live-boxes, and examined in about a day. At that time, a large number of attached and metamorphosing larvae should be present.

A. The Ovum: The ripe eggs measure 40 by 50 by 60 microns, the shortest axis being apico-vestibular.

B. Fertilization and Cleavage: There is some disagreement as to whether the colonies are bisexual or unisexual (see "Living Material" above). Marcus (1939) suggests that they are unisexual, although hermaphroditism occasionally occurs. Fertilization is internal, and at least the first maturation division occurs within the ovary. After its release from the ovary, the egg passes through a short vagina where it is enclosed in a soft shell with a long stalk. The shelled eggs are attached by means of the stalks to the floor of the brood-chamber, which consists of the walls of the vestibule between the tentacles and the vestibular groove. Cleavage is equal and spiral, closely resembling that of the annelids. Five quartets of micromeres and one quartet of macromeres are produced (Hyman, 1951). A hollow blastula is formed by the 67-cell stage. Gastrulation is by invagination and starts at about the 90-cell stage.

C. Later Stages of Development: Following gastrulation, there is an apical-oral elongation of the embryo, accompanied by closure of the slit-like blastopore. An apical plate, bearing cilia, develops at the aboral pole but invaginates by the time the larva is set free. Shortly after this organ is formed, the stomodeum and proctodeum invaginate on the oral surface, and the pre-oral or dorsal organ appears as an invagination on the anterior side of the larva above the mouth. At this time, the egg shell vanishes and the larva is freed. When released, the larva swims with the aid of an oral ring of strong cilia, the corona. The digestive tract is complete and feeding occurs. Shortly after release, a well-marked invagination appears between the mouth and anus. This is the vestibule or atrium; it is bordered by the corona. Both the mouth and the anus are borne on long projections called the epistome and anal cone, respectively.

After about a day, the free-swimming larvae attach by means of the atrial surface, and undergo a complicated metamorphosis which involves a degeneration of the apical plate and dorsal organ, and a complete upward rotation of the entire larval body. For further details concerning the larvae and metamorphosis, see the papers by Harmer (1887) Cori (1933) and Hyman (1951).

CORI, C. J., 1933. Dritter Cladus der Vermes Amera. Kamptozoa. Allgemeines fiber den Cladus Kamptozoa. Erste und einzige Klasse des Cladus Kamptozoa; Kamptozoa = Bryozoa Entoprocta=Calyssozoa. Kükenthal Handbuch d. Zool., 2: Hft. 1 (5), 1-64.

HARMER, S. F., 1887. On the life-history of Pedicellina. Quart. J. Micr. Sci, 27: 239-263.

HATSCHEK B., 1877. Embryonalentwicklung und Knospung der Pedicellina echinata. Zeitschr.f. wiss. Zool., 29: 502-549.

HYMAN, L. H., 1951. The Invertebrates: Acanthocephala, Aschelminthes, and Entoprocta.

The Pseudocoelomate Bilateria. McGraw-Hill Book Co., Inc., New York.

MARCUS, E., 1939. Briozóarios Marinhos Brasileiros. III. Boll d. Fill Cien., e Let., Univ. de Sao Paulo, Zool., 3: 111-291.