Reproductive biology

Asexual reproduction is responsible for colony growth and regeneration of zooids. Each colony begins from a single, sexually produced larva that settles and metamorphoses into a founding zooid, called the ancestrula. The ancestrula undergoes budding to produce a group of daughter zooids, which themselves subsequently form more buds, as do succeeding generations. Budding involves only elements of the body wall. The developing bud originates from the parent zooid. The bud initially includes only components of the body wall, or cystid, and an internal coelomic compartment. A new polypide is then generated from the living tissues of the bud, that is, the epidermis and the peritoneum. The epidermis and peritoneum invaginate, the former producing the lophophore and the gut. The peritoneum produces all of the new coelomic linings and the funiculus. Most gymnolaemates are hermaphroditic. Testes and ovaries develop either within the same zooid (zooidal hermaphroditism) or in different zooids within the same colony (zooidal gonochorism). In

A variety of lace corals with their zooids extended, growing under a ledge near Heron Island, Great Barrier Reef. (Photo by A. Flowers & L. Newman. Reproduced by permission.)

usually is a seasonal specialization involving the polypide. In gonochoric zooids, sexual polymorphism is permanent and involves specialization of the cystid, zoecium, and sometimes the polypide.

Gymnolaemates have a variety of brooding methods, usually involving formation of an external brooding area called an ovicell, or ooecium.

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