Dragonfly larva, chaser or skimmer?

Dragonfly larva, chaser or skimmer?

Observation - Dragonfly larva, chaser or skimmer? - Global. Description: Dragonfly larva from temporary pond with bare mud clay substrate. In the pond the larvae have a covering of clay, as shown in the picture. I have looked at my field guides and, taking into account the habitat think maybe black-tailed skimmer or broad-bo

Dragonfly larva from temporary pond with bare mud clay substrate. In the pond the larvae have a covering of clay, as shown in the picture.
I have looked at my field guides and, taking into account the habitat think maybe black-tailed skimmer or broad-bodied chaser, but don't have a crystal clear photo of any dorsal spines and just can't quite get the 'jizz' from the photos in my books.
Anyone familiar enough with these little lovelies to help with a confident ID?
Many thanks!