hydranth


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hydranth

[′hī‚dranth]
(invertebrate zoology)
Nutritive individual in a hydroid colony.
References in periodicals archive ?
One frustule was observed "in vivo" budding off from a hydranth and was estimated to grow approximately 130 [micro]m in four and a half hours (from 300 to 530 [micro]m) to finally detach overnight at 537 [micro]m in length.
After two days in captivity a bud from the "[a.sub.1]" hydranth was observed, whereby the entire process through the complete release of the frustule lasted less than 14 hours.
Whether the large sclerotized region of colony (a) corresponded to a third hydranth that had previously died but remained fixed would need further observations.
Hydranth ovoid, whitish, with 14 tentacles, each about 400 [micron]m long.
Hydranth yellow or pale, spherical, with 25-28 tentacles, about 810 [micron]m long each.
Hydranth soft brown or pale, small, cylindrical, about 320 [micron]m from diaphragm to tentacles.
Colonies also grow asexually by producing additional hydranths to the upright branches (hydrocauli) or by extending the attached stolons (hydrorhiza) that then produce more hydrocauli and hydranths (Kinne, 1958; Fulton 1962; Jormalainen et al., 1994).
The branching pattern of the colony, its size, the width of hydranths, the diameter of tentacles, and the shape and number of cells all seem to respond to salinity.
--In order to find out whether, when the oral end is tied, changes take place throughout the piece that tend to make more rapid the development of basal hydranths, or whether these changes are localized at the basal end where the new hydranth develops, the following experiment was tried.
After 23 hours the hydranth region at the oral end was cut off of some pieces (A), others were cut in two in the middle of the piece (B), and for a control some pieces were left as before (C).
The mean density of zooxanthellae per hydranth cell was 2.67.
The number of unhealthy looking zooxanthellae per hydranth digestive cell showed a broad peak at about midnight (four highest data points = 1.04 [plus or minus] 0.14 unhealthy looking zooxanthellae/cell), and reached a broad low during the day (four lowest data points = 0.72 [plus or minus] 0.05 dead zooxanthellae/cell).