FIGURE 29.11
The life cycle of the hydrozoan Obelia. 1 The polyp reproduces asexually by budding to form a colony of interconnected polyps (inset, LM). 2 Some polyps, equipped with tentacles, are specialized for feeding. 3 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusas by asexual budding. 4 The medusas swim off, grow, and reproduce sexually. 5 The zygote develop develops into a solid, ciliated larva called the planula. 6 The planula eventu ally settles and develops into a new polyp. The polyps stage is asexual, the medusa stage is sexual, and these two stages alternate, one producing the other. But do not confuse this with the alternation of generations that occurs in the plant kingdom. Both polyp and medusa are diploid organisms, whereas one of the plant generations is haploid.