annulate

It is highly contractile and when contracted sometimes assumes an annulate appearance; but as a rule the external surface is smooth.

The gills are broad and free from the stem, sometimes anastomosing near it, white; stem white, hollow, tapering towards the cap, annulate.

This is a beautiful species, easily known by its discoidal or almost annulate sporangia mounted upon short dark black stipes.

The longitudinal type characterises such genera as Vibrio, Filaria, Gordius, and all the annulate animals.

Cross rings may or may not be present, and the cup is either smooth or annulate.