Scientific Name:               Spongilla spp.
Common Name(s):         Freshwater Sponge

©Lamiot

Identification:

Freshwater sponges are sessile (non-moving) multicellular organisms with a branching moss-like body. They do not have organs but have specialized flagellated cells (cells with waving ‘tails’) that help them filter food from water. They are often mistaken as algae but are coarse, whereas algae are slimy. However, algae live on freshwater sponges’ branching limbs, giving them a greenish color. They are also distinguished from algae by their gemmules. Gemmules are internal buds used in asexual reproduction, where each bud can grow into a new mature sponge. These gemmules are the main feature used to disguise among the 20 species in the genus Spongilla. They can grow up to 150 cubic inches.

Range:

Spongilla spp. are found worldwide. Freshwater sponges can be found in the United States and Canada. Some species have a wide range and can be found in many other countries including Egypt, China, Russia, Germany, and others.

Ecology:

Freshwater sponges are found on submerged rocks and logs in ponds, lakes, and slow-moving streams. They are filter feeders, filtering water to eat microscopic protozoans and bacteria. Water is ushered through the tiny outside pores (ostia) into the body cavity by specialized flagellated cells which create an inward current. The water current flows throughout the sponge’s body bringing food particles into the cells and carrying waste away. Because they are filter feeders, they prefer to live in pristine water so may be an indicator of water quality.

Unlike saltwater sponges, freshwater sponges can become dormant in adverse conditions, such as drying or excess cold, and form gemmules. Gemmules are formed as a means of asexual reproduction and as a survival mechanism, as they can withstand extreme drying and cold. Gemmules are similar, in theory, to seeds. When conditions improve, these seed-like gemmules will grow into new sponges. Freshwater sponges usually become dormant in the fall.

Algae and freshwater sponges have a symbiotic relationship, where they live together and both parties benefit. The algae receives a secure substrate to attach to and the sponge ingests waste created by the algae.

Special Notes:

Here in Bella Vista, freshwater sponges will most likely be found in spring-fed, small, slow-moving streams, near springs which enter our lakes, or springs that feed Tanyard Creek. Species found in Arkansas include: Ephydatia mulleri, Trochospongilla leidyi, and Trochospongilla horrida (River Rock Sponge). These species were found in Savoy, Elkins, Washington County, Scott County, Eden’s Bluff, Petit Jean River, and the White River. Freshwater sponges prefer clear lakes and streams and have been found in Arkansas on the underside of submerged timber, but are mainly on the tops of rocks.