This is Chondrus crispus, aka Irish moss or Red moss.
The delightful reds in this seaweed and the gorgeous shapes were too hard for me to resist.
Here is the complete weed on a sea background made of the soft wrappings used by florists to wrap bouquets.
The model has two sides, ‘front’ (above) and ‘back’ (below).
Below are the nets I used to assemble the complete weed partially shown above.
First the front nets.
Then the back nets.
The only problem is it took me about six hours to assemble one weed from the printed nets. Cutting has to be precise.
The complete weed did not fit my scanner so, alas, the holdfast is not shown.
A friend has suggested populating the weed with fish, specifically clownfish. This may prove to be an irresistible challenge.