5), the blastostyles gradually lose their nutritive function and the organs connected with it; the mouth and tentacles disappear, and the blastostyle obtains the nutriment necessary for its activity by way of the coenosarc. In the Calyptoblastea, where the polyps are protected by special capsules of the perisarc, the gonothecae enclosing the blastostyles differ from the hydrothecae protecting the hydranths (fig.
- 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.