Members of this genus are found in the Pacific, Atlantic, Indian, Arctic, and Southern oceans.

The number of these secondary tentacles is reported to vary across the different species.

Species in this genus also have eight large pads known as anchors located between the arms.

These vary in size and shape and currently play in important role in differentiating one species from another.

Some, but not all, species in this genus have prominent white nematocyst clusters.