Further study of reproductive compatibility and morphometric features (e.g., branching pattern and hydrocaulus
length) may provide some means of separating lineages in this cosmopolitan invasive species.
Decreasing temperatures cause the tissue of hydroids to regress into a small section of hydrocaulus
or hydrorhizae, which regrow when favorable temperatures return (Gili & Hughes 1995).
always unbranched, monosiphonic, divided by internodes at regular intervals.
Newly settled individuals that did not develop to hydrocaulus
and hydrorhiza elongation retained small numbers of AIs in the aboral tentacle tips (Al, 16.1 [+ or -] 13.1; S, 199.3 [+ or -] 60.9; D, 168.6 [+ or -] 54.7; MM, 35.9 [+ or -] 16.5; the total, 419.8 [+ or -] 71.8).