Spanish researchers have published the discovery of a sponge reef unique in the world. These structures, which are thought to be extinct for millions of years, has been found to 760 meters deep, surrounding  small underwater mountain between Valencia and Ibiza, where there is oil drilling plans.

The small seamount is located in an area where there are plans to polls hydrocarbons, and is formed by the species Leiodermatium pfeifferae, sponge so far only known in the Atlantic, from Macaronesia to the Caribbean, so also it is the first report of this species in the Mediterranean.

Silica reefs built by sponges rather than corals were common in the Jurassic and Cretaceous seas, and were believed extinct. To general surprise, in 1987, a live coral silica reef was discovered at 200 m depth in the Canadian Pacific coast, formed by Hexactinellid sponges (“glass sponges”).

The discovery of the reef has been made by a ROV aboard the Oceana Ranger, allowing filming and collecting information on the species associated with this ecosystem, like other sponges, corals, gorgonians, corals deep, conger eels, etc.


Cloud Sponge (Aphrocallistes vastus)

…is a species of glass sponge found throughout the northern Pacific Ocean. Cloud sponges are one of the few species of glass sponges that are able to form slow growing reefs. They provide a substrate that a community of invertebrates and other animals can thrive on. Like all glass sponges the cloud sponge’s body wall is made of silicaceous material which makes it unattractive as a meal to most predators, however a few species of sea stars are know to prey on it.



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Venus’ Flower Basket - Euplectella aspergillum

This is the bleached skeleton of the Venus’ Flower Basket, Euplectella aspergillum, belonging to the small group of glass sponges (Hexactinellida - Euplectellidae), characterized by a skeleton composed of microscopic, silica spicules. 

The body structure of these animals is a thin-walled, cylindrical, vase-shaped tube with a large central atrium. The body is composed entirely of silica in the form of six-pointed siliceous spicules, which is why they are commonly known as glass sponges. Spicules are microscopic, pin-like structures within the sponge’s tissues that provide structural support for the sponge. These spicules ‘weave’ together to form a very fine mesh which gives the sponge’s body a rigidity not found in other sponge species and allows glass sponges to survive at great depths in the water column. Overlying the spicule framework there is more siliceous tissue called a syncytium which forms very fine fibres which look rather like a cobweb over the framework.

Venus’ Flower baskets are deep sea animals found in the western Pacific Ocean near the Philippine Islands.

References: [1] - [2]

Photo credit: ©Martyn L Gorman

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What makes the 3 classes of sponges unique?

Imagine diving on a tropical coral reef and seeing all sorts of colorful sponges, some large, some small, some barrel shaped and some tube shaped. You might wonder: are all of these sponges functioning in a similar way? Do all sponges look like these? The answer is no, not even close.

There are three classes of sponges, all within one phylum called Porifera. Almost all of these filter water to obtain food - like the ones we focus on for our project exploring how sponges change the water chemistry on coral reefs - but some use a different life strategy altogether.

Sponges in all three classes have microbes that live within them as symbionts (symbionts are organisms of different types that live/exist together). This is an important relationship for sponges and an important concept for our project!

First, the class Demospongia comprises the largest and most widespread group of sponges and these are what people typically think of when they think of sponges. Demosponges have silica (glass) spicules that help give structure to the sponge body (like a skeleton) and protein fibers called spongin, which gives them a resilient quality. Demosponges come in all sorts of sizes, shapes and colors as shown in the photo below.

  • Photo courtesy of Saspotato on Flickr under the creative commons license 

They are found in tropical, temperate, polar, shallow, and deep water, and in freshwater. The sponges that were harvested (and still are on a smaller scale) for bathing belong to the genera Spongia and Hippospongia, are also a demosponges but these have no spicules.

  • Historical photo of sponge auction in Key West. Photo courtesy of Florida Sea Grant on Flickr under the creative commons license.

One unique demosponge I want to mention here is the carnivorous kind. Yes, I said carnivorous sponges! These typically live in deep water were there is less food in the water column. Theses sponges have hooked spicules that help them capture small crustaceans – like shrimp and amphipods, and even small fish! You can think of these as a sponge version of the venus fly trap plant.

The harp sponge is carnivorous and was discovered in 2012 off the coast of California at over 3,000 m depth by Monterey Bay Aquarium Research Institute. See more info here

Pictured below is one kind of carnivorous sponge, courtesy of NOAA photo library, that can trap small animals with filaments (typically seen with long filaments not shown here) that readily capture small animals that have fine hair-like appendages called setae.

  • NOAA photo library, creative commons license

The second class is Hexactinellida, or the glass sponges. These have silica spicules, which are often quite large and beautiful with 4 to 6 points on each spicule. The glass sponges are typically found in deeper waters (>1,000 ft or 300 m) and can form large reefs, such as found in deep water off the coast of British Columbia and Washington state.

Rather than pumping, these sponges rely on current to move water through their bodies so they can capture particles of food. They have a unique characteristic of being able to rapidly send electrical signals across their bodies so that they can respond to stimuli- perfect for grabbing that fast moving piece of detritus!

  • Venus’s flower basket glass sponge. Photo courtesy of NOAA photo library on Flickr under the creative commons license

One unique example of a glass sponge is the species known as Venus’s flower basket (pictured above). This sponge has a symbiotic relationship with a small shrimp. Two shrimp, one male and one female, live inside the sponge their entire lives. When the shrimp produce offspring (larvae), the larvae are released and travel to find another sponge to settle in. The shrimp get a great home with constant food supply and they help clean the sponge.

The last class is Calcareathe calcareous sponges. The spicules in these sponges are made of calcium carbonate rather than silica. These are less common than demosponges but still found in marine waters worldwide, even in shallow water that you might dive in.

The photo below is from a NOAA Ocean Exploration cruise that I participated in that was organized by researchers at The South Carolina Department of Natural Resources and the College of Charleston’s Grice Marine Lab. The lovely looking calcareous sponge we collected using the submersible The Johnson Sea Link II was from ~150 m depth off the coast of Georgia and South Carolina is pictured below (On the left side of the calcareous sponge is another kind of sponge).

This guest-post is written by Cara Fiore (@clfiore). 
Cara is a post-doctoral researcher at Woods Hole Oceanographic Institute. Among other things, she studies how sponges influence water chemistry in reefs (and elsewhere). You can learn about her ongoing research at experiment.com/sponges.


Certainly not.  They have skeleton made of silica, which is the same material used to make glass, but in glass sponges are not glass, per se.

Glass sponges, or hexactinellids, belong to the phylum Porifera. These animals are common only in the deep ocean. Their tissues contain glass-like structural particles made of silica. The many tiny siliceous elements of a glass sponge’s skeleton are called “spicules.” Unlike most sponges, glass sponges produce extremely large spicules that fuse together in beautiful patterns to form a “glass house”; a complex skeleton that will often remain intact even after the sponge itself dies.

  • Photo: The primary skeleton of many glass sponges is a network of large spicules that have fused together to form a matrix that defines the overall body shape of the sponge. courtesy of G.P. Schmahl.
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