Answer the following question given this paragraph: 

Hydrozoa includes nearly 3,500 species, most of which are marine. Most species in this class have both polyp and medusa forms in their life cycle. Many hydrozoans form colonies composed of branches of specialized polyps that share a gastrovascular cavity. Colonies may also be free-floating and contain both medusa and polyp individuals in the colony, as in the Portuguese Man O’War (Physalia) or By-the-Wind Sailor (Velella). Other species are solitary polyps or solitary medusae. The characteristic shared by all of these species is that their gonads are derived from epidermal tissue, whereas in all other cnidarians, they are derived from gastrodermal tissue (Figure 15.14ab). “The Hydrozoa Directory,” Peter Schuchert, Muséum Genève, last updated November 2012, http://www. ville-ge. ch/mhng/hydrozoa/hydrozoadirectory.


Q: Most hydrozoa have both polyp and what forms in their life cycle?


A:
medusa