Uncertain future for green alga freeloading on Eastern Snake-necked Turtle

I'm assuming the green algae attached to the shell of this Eastern Snake-necked Turtle in Lake Alexandra, Mittagong, in the Southern Highlands of New South Wales, is Basicladia ramulosa. At least that that's the best name we have at the moment for a species of algae found throughout most of continental Australia.

The problem is, there are a few different green algae of this sort (in the family Cladophoraceae) found growing on the shells of animals. Some favour turtles, others bivalves (mussels). The historical approach has been to allocate them to two different genera, depending on where you find them: Arnoldiella on bivalves and Basicladia on turtles. 

Turns out the substrate - what they grow on - is not so important. The latest molecular analysis, , in 2012, gathers them both together in a single branch with a presumed common ancestor. The fact they are epizoic, growing on animals, does turn out to be an interesting shared trait, found only rarely elsewhere in the family (there is another species elsewhere in the tree that favours shrimps). 

These freeloading algae don't seem to harm animal, although presumably they slow them down a little. For the alga, it probably provides some useful water movement across it's surface, like living in a slow-flowing stream which is exactly where some of its relatives turn up.

I was a co-author of a paper in 2008 (four years before the paper rolling it into Arnoldiella) where we excitedly reported a new locality for our endemic Australian species, Basicladia ramulosa, a species described by my late friend and colleague Sophie Ducker in 1958. Back then there was some residual dispute about whether it should rolled into the much bigger genus Cladophora.

So, this animal loving group of 'Cladophoracean algae' (I'm sorry there are no simpler words to use, but think green, branched filaments, of the the kind that bind together into what we sometimes call blanket weed when it coats rocks in usually polluted streams of southern Australia) are now a single genus.

But, unfortunately, our Australian species ends up just outside this new generic grouping, with a more widespread species Basicladia okamurae further out again. Ours could be rolled up into Arnoldiella without fuss - it would still be what we call a monophyletic group (all known species with presumed shared ancestor) - but the other one is more complicated as to make it monophyletic would drag in various other well respected and circumscribed genera of Cladophoraceae).

Suffice to say that until we know a little more about these two species and a few other branches in the tree these two species have been parked as insertae sedis, a Latin phrase meaning we just don't know. So Basicladia ramulosa might be an Arnoldiella or it might be something else.

If something else, sadly it can't be Basicladia. The type of that genus - the species on which the genus name is always attached and which helps us sort of nomenclature - is definitely within Arnoldiella, which means it is no longer available unless we 'conserved it with a new type'. That option is generally not encouraged because it tends to further complicate resolving any names you might find in the old published literature. 

For now then we can call this alga on the back of an Eastern Snake-necked Turtle, 'Basicladia ramosa inc. sed.'. Or perhaps that green algae I saw on the back of a turtle the other day. Given I haven't looked at it under the microscope anyway, perhaps that second sentence is the safest.

That other day for me was in Christmas 2020, when I was visiting family in Sydney and took a wander around the lovely Lake Alexandra. It was a bugger to photograph, as you can see.

A week or so later I was rushing back to Melbourne to meet the New Year's Eve curfew, spending the night on the Hume Highway with midnight celebrated in the Burnley Tunnel. But beside Lake Alexandra, all was calm.