Taxon of the Day: Spongillidae

River sponge or Ephydatia fluviatilis 

Some interesting species live in our neighbourhoods and remain unnoticed just because their habitats are not very convenient to look at. This can be any place we pass-by every day. Stopping for a few minutes in these familiar spaces and taking a second look from a different perspective may lead to small discoveries. Freshwater sponges are a case in point as today’s Taxon of the Day species were observed from a small bridge over the River Thames in Reading, UK.  Spongilla lacustris (Linnaeus, 1759) or Lake sponge and Ephydatia fluviatilis (Linnaeus, 1759) or River sponge, are the two most reported freshwater sponge species in the UK, although some foreign references suggest a possible 4-6 species could inhabit rivers and lakes of the United Kingdom.

River sponge or Spongilla lacustris

There are an estimated 8-10,000 known species of sponges worldwide all classified under the four classes of phylum Porifera: Calcarea, Hexactinellida, Demospongia, and Homoscleromorpha. 

Sponges come in an incredible variety of shapes (eg sheets, mounds, tubes), sizes (1mm to 1m) and colours, and mostly live in a marine environment. However, there are over 150 freshwater species worldwide. All of the freshwater species belong to the class Demospongia, order Haplosclerida. The sponges that can be observed in the Thames are actually cosmopolitan species found all around the world representing family Spongillidae.

Sponges are mostly filter feeders (although a few are also predators) passing large volumes of water through their bodies. Water enters through multiple small pores called ostia, flows through canals to a spacious chamber, and finally exits through large opening called osculum. Sponges have no specialized organs, no nerve system or muscles. It’s no wonder Aristotle and naturalists thought they were plants until the 19th Century when it was proven that they are actually animals.

Etymology: Spongilla lacustris from the Latin lacus meaning lake, and Ephydatia fluviatilis from the Latin fluvius meaning river.

The Catalogue of Life lists 8,401 species of sponge taken from the The World Porifera Database.

CoL Annual Checklist: Spongillidae

CoL contributor: World Porifera database

Image copyright: Viktoras Didziulis
Source text:  Freshwater sponges in the River Thames pg34-40