Thongweed

Thongweed

Observation - Thongweed. Description: There were a number of these on the rocks at the low tide mark about 20-25mm across. I assume they are part of a seaweed, would be interest to know more?

There were a number of these on the rocks at the low tide mark about 20-25mm across.
I assume they are part of a seaweed, would be interest to know more?