Golden Algae

Forty years ago, when I was a university student, life – more specifically, cataloguing life – was relatively simple. Living organisms fell into one of five kingdoms: bacteria, plants, animals, fungi ................and protists, which were a rag-bag of mostly small organisms that no one knew enough about to be able to fit them into any of the other four categories. The science of classifying living organisms and understanding their evolutionary relationships has moved on, thanks to our ability to look at species’ relationships by comparing their DNA sequences.......which has made classifying life more intriguing and much more complicated. Those rag-bag protists are now subdivided by biologists into several kingdoms, one sub-division of which contains this lovely little organism, less than a millimetre long and called Dinobryon, which is known as a golden alga (or Chrysophyte). There are now thought to be about a thousand different Chrysophyte species, mostly single-celled, but this is one of the more complex types. They all have a golden yellow pigment called xanthophyll, which you can just about detect in the top photo of Dinobryon. This organism, which is common around pond and lake edges, consists of individual cells, each with a couple of lashing flagellae (which you can just about make out poking out of the uppermost 'vase' in the bottom photo), with each cell encased in a glassy vase and attached to a branching stem. The top photo is taken with polarised light, which generates the lurid interference colours, while the bottom one is taken with interference contrast microscopy, which gives better resolution of the individual cells in their ‘vases’.