The column (b) is generally long, slender and stalklike (hydrocaulus).
The perisarc when, present invests the hydrorhiza and hydrocaulus; it may stop short below the hydranth, or it may extend farther.
As a general rule polyp-buds are produced from the hydrorhiza and hydrocaulus, while medusa-buds are formed on the hydranth.
Budding from the hydrocaulus may be combined with budding from the hydrorhiza, so that numer ous branching colonies arise from a common basal stolon.
The body bears tentacles, but shows no division into hydrorhiza, hydrocaulus or hydranth; it is temporarily fixed and has no perisarc. The polyp is usually hermaphrodite, developing both ovaries and testes in the same individual.