They have hydrorhiza connected to tubular stolons attaching them to other objects,[2] like algae, kelp, rocks and crabs.

Hydranthea have small smooth hydrophores placed irregularly along their hydrorhiza, of variable length - though they tend to be shorter.

[5] Hydranthea are active and capable of stretching their tentacles, tending to bend to touch the substrate they are rooted in when disturbed.

[8] Latest databases accept the species as Hydractinia phialiformis[9] (Antsulevich, 1983), a separate genus from Hydranthea.

[12] Species found in the Mediterranean Sea, notably Hydranthea aloysii, have been cited with high confidence (≤95%) to be extinct, or at least extremely rare, due to their lack of sightings in recent scientific literature about the region.