Complex sentence: They are difficult to detect and if capable of forming halos the cloud takes the form of thin cirrostratus nebulosus and have a fibrous texture with no haloes if it is thicker cirrostratus fibratus.
Split into simpler sentences: They are difficult to detect and if capable of forming halos the cloud takes the form of thin cirrostratus nebulosus. The cloud has a fibrous texture with no haloes if it is thicker cirrostratus fibratus.