Demospongiae

Overview

Demospongiae represents the dominant class of living sponges, representing more than 90% of all those alive today. Few demosponges have hard skeletons, leaving behind a sparse fossil record compared to other classes. The clade is, however, very diverse, with over 7000 living species. Many demosponges support other organisms (including sea turtles and angelfish) by being a source of food.

Demosponges have the most complex sponge body form with monoaxon or tetraxon spicules. With the majority of spicules made of silica, this class is included in the major sponge group Silicea.

Demospongiae has a long fossil record dating to the Early Cambrian. Fossil demosponges are prevalent in Permian and Cretaceous rocks.

Bath Sponges (Spongidae)

Some sponges lack spicules altogether, creating a soft 'spongy' structure ideal to be used as a cleaning tool. Although our household sponges are manufactured from synthesized materials now, they used to come from natural sponges belonging to the family Spongidae. Spongidae has an affinity for warm waters, where the sponge industry has over exploited them in some regions. The video below shows how natural sponges were once fished for and sold.

Boring Sponges (Clionidae)

Not all sponges are boring! (pun intended!) Have you ever seen a seashell on the beach covered in tiny holes? Excavating (or boring) sponges (Clionidae) are likely to blame. This family of sponges use acid to etch out the calcium carbonate of shells and other surfaces to create a home.

Redwoods of the Reef

Giant barrel sponges, such as Xestospongia muta, are referred to by some as "Redwoods of the Reef." This group of sponges are known to reach massive sizes and ages of 2000 years or more in warm Caribbean seas (Van Soest, 2012).

Freshwater Sponges (Spongillidae)

Freshwater sponges (suborder Spongillina) inhabit virtually every kind of freshwater habitat across every continent except Antarctica. They have been found at depths of hundreds of meters in lakes, to encrusting surface rocks along streams, to swamps and even alpine water bodies. These hardy creatures are everywhere, with the greatest diversity rooted in the Neotropoic and Palaearctic regions. The oldest fossils of this family date back to the Carboniferous, but there has been a boom in diversity since the Eocene (56 million years ago).

NEWS: Eye Lesion Outbreak in Brazil

Although most sponges are harmless, their sharp spicules can be irritants. In 2005, the Brazilian Ministry of Health called for a multidisciplinary team of researchers when 59 people developed eye lesions after swimming in the Araguaia River in the Tocantins state of Brazil.

Most of the affected were children who experienced itchy, burning sensations in their eyes after swimming in the river and most developed eye lesions a few weeks later. Initially, a water borne disease or parasite was suspected. After a year of intensive research, however, it was determined that freshwater sponge spicules were causing the outbreak. The local area has a known sanitation problem where sewage treatment plants were once being constructed but never finished. During tourist season this becomes an exacerbated problem. An invasive clam species unaffected by these conditions rapidly populated the area, preventing sponge larvae from settling on the river bottom. Without attachment, the larvae disintegrated, causing loose spicules to float in the water and into the eyes of the swimmers (Cruz et al., 2013).

Carnivorous Sponges (Cladorhizidae)

Carnivorous sponges have traded their choanocyte water current system for a sticky outer surface to capture prey. Long hooks act like Velcro, trapping unlucky small invertebrates passing by, which become the sponge's next meal. With no digestive system, individual cells slowly break down the prey at the cellular level. Carnivory seems to be a sponge adaptation to living at great depths, where other particles may be more difficult to come by. Watch the video below to learn about four species of carnivorous sponge!

Fossil Demospongiae

References and further reading:

Bergquist, P.R., and J.H. Bedford. 1978. The incidence of antibacterial activity in marine Demospongiae: Systematic and geographic considerations. Marine Biology, 46: 215-221.

Boardman, R.S., Cheetham, A.H., and Rowell, A.J. 1987. Fossil Invertebrates. Blackwell Scientific Publications. 713 pp.

Botting, J.P, and Muir, L.A. 2018. Early sponge evolution: A review and phylogenetic framework. Palaeoworld: 27, pp. 1-29.

Brusca, R.C., and G.J. Brusca. 2002. Invertebrates Second Edition. Sinauer Associates Inc. Publishers, Sunderland MA. 936 pp.

Cruz, A., Alencar, V., Medina, N. et al. 2013. Dangerous waters: outbreak of eye lesions caused by fresh water sponge spicules. Eye 27, 398–402.

Lundsten, L., Reiswig, H.M., and Austin, W.C. 2014. Four new species of Cladorhizidae (Porifera, Demospongiae, Poecilosclerida) from the Northeast Pacific. Zootaxa 3786 (2): 101-123.

Van Soest, R.W.M., et al. 2012. Global Diversity of Sponges (Porifera). PLoS ONE: 7(4), pp. 1-23.

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Unless otherwise indicated, the written and visual content on this page is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. This page was written by Jaleigh Q. Pier. See captions of individual images for attributions. See original source material for licenses associated with video and/or 3D model content.