- Trophosome without hydrothecae or gonothecae, with monopodial type of budding.
SUB-ORDER HYDROIDEA CALYPTOBLASTEA (LEPTOsome with polyps always differentiated into nutritive and reproductive individuals(blastostyles) enclosed in hydrothecae and gonothecae respectively; with sympodial type of budding.
These organs are supported by cuplike structures of the perisarc, termed nematophores, regarded as modified hydrothecae supporting the specialized polyp-individuals.
- Tropho so m e with stalked hydrothecae; gonosome, free medusae with otocysts and four, rarely six or eight, unbranched radial canals.
- Hydrothecae sessile, biserial, alternating or opposite on the stem.
- Hydrothecae sessile, biserial on the main stem, uniserial on the lateral branches or pinnules, which give the colony its characteristic feathery form; with nematophores.
The supposed hydrothecae may be present on one side of the axis only (monoprionid) or on both sides (diprionid); the first case may be conjectured to be the result of uniserial (helicoid) budding, the second to be produced by biserial (scorpioid) budding.