Pe baech chi’n codi carreg yn yr ardd, gobeithio y byddech chi’n dod o hyd i lawer o wrachod y lludw. Mae gan y trychfilod gwydn yma arfogaeth fewnol ac maen nhw’n hoffi cuddio mewn llecynnau…

Often confused with the larger but similarly shaped lion’s mane jellyfish, the blue jellyfish can be colourless when young and develop a striking blue-purple bell as it matures.

This colonial creature looks like an old-fashioned quill - that's where the name sea pen comes from.