mick's picture

Gelatinous growth on underside of rocks in River Thames

Observed: 17th November 2009 By: mick
London Natural History Society
mick’s reputation in Invertebratesmick’s reputation in Invertebrates
2009 1117 122038 Gelatinous growth on underside of rocks
Description:

The tidal Thames at Richmond is normally kept at quite a high level by barriers on Richmond Lock. These haven't been in place recently, so the river has been very low at low tide. We turned over some large rocks on the river bed, and found some covered in what looked like a gelatinous resupinate lichen, firmly stuck to the rock. These were only on the underside of the rock. Photo attached of a small piece, maybe 30mm across, but there were large growths on the same rock

Identifications
Species interactions

No interactions present.

Comments

mick's picture

Richmond sponge

Thanks, I thought it might be a sponge, and yes it did have that glass/grit feel to it. My other thought was a bryozoan, but there was no hand-lens visible structure to it. Sponges are microscope jobs I think. I certainly thought it was an animal rather than plant or algae.

I found a reference to Trochspongilla horrida that is flat, encrusting and yellow/brown. Penney and Racek (1968) wrote a recent(?) US paper on freshwater sponges.

I suppose we should look for Sisyridae (sponge-fly) larvae and, next spring, adults in the area.

Many thanks, very interesting.
M.

John Bratton's picture

T. horrida is not on the NBN

T. horrida is not on the NBN species lists so is probably not found in Britain. The two species you most often see mentioned in GB are Spongilla lacustris and Ephydatia fluviatilis, but I don't know how often they are properly identified. It may be that because they are the ones that are most often depicted in books, they get over-recorded.

Yes, it is worth looking for sponge flies next summer. One species is fairly common.

John

mick's picture

Sponge literature

John,
I have a copy of Fitter & Manuel 'Lakes, Rivers, Streams and Ponds'. That is where I saw the description for T horrida. The only photograph is of E fluviatalis and that does not look right at all. I'll have to find a small rock with a specimen. The one I photographed is on a big rock, too big to lift. As if I don't have enough to do !!
Thanks, Mick.

marymb1's picture

fresh water sponge

I have posted a couple of photographs and of what I thought was a fresh water sponge but they don't look anything like the ones on these pages. Is there a large variety in the UK- google doesn't help. Can you?
Thanks