Naturally, it is among the free living forms that the parapodium is best developed, and least developed among the tubicolous belongs typically a long tentacle, the cirrus, which 'r podium or neuropodium, and may be developed into an arborescent gill or into a flat scale-like process, A the elytron (in Polynoe, &c.).
Among the burrowing and tubicolous forms it is not uncommon for the body to be distinguishable into two or more regions; a "thorax," for example, is sharply marked off from an "abdomen" in the Sabellids.
Frequently the foot is ciliated at the tip, as in the young of tubicolous forms.
Melicertaceae; females tubicolous, usually attached, or forming spherical floating social aggregates; males free swimming.
(a) Floscularidae; tubicolous, with a lobed disk, bearing stiff or vibratile setae.
Others - the majority - live among weeds, the tubicolous ones mostly upon them.
Leeuwenhoek found and described some tubicolous species; and during the 18th century a fair number of species were observed, figured and described with names.
At first supposed to be tubicolous Annelids, Dentalium and its allies were afterwards placed among the Gastropoda, to which recent authorities consider them to be closely related.