Reproductive biology

The life cycle includes both sexual and asexual reproduction. During the brief season of sexual activity, sperm are formed on the funiculus and then detach to circulate freely within the colony. Grape-like clusters of eggs appear on the inner colony wall near the tip of certain zooids. Internal fertilization appears possible, but there is also evidence of outcrossing. The mechanism for sperm exchange between colonies is unknown. The fertilized egg develops within a special embryo sac, becoming a motile stage composed of one or two fully formed zooids surrounded by a ciliated mantle. Once released from the colony, this larva-like structure can swim actively for several hours before settling on a substrate. The mantle pulls back, and the new zooids begin feeding almost immediately.

In some species asexual reproduction may be as simple as fragments of the colony lodging in a new location. In some globular species the colonies may pinch off daughter colonies, which then glide slowly away. However, all species also engage in asexual production of dormant statoblasts capable of withstanding drought, freezing temperatures, and other unfavorable conditions. Many statoblasts contain air chambers that provide buoyancy, so on release from the colony, they can drift considerable distances or adhere to feathers of waterfowl. Another type of statoblast is attached directly to the substratum, where it remains long after the colony has disintegrated. The period of obligate dormancy can last several months, and some statoblasts remain viable for years. When favorable conditions resume, the statoblast germinates to produce a single zooid capable of forming a new colony.

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