Caribbean Coral in the Mesoamerican Reef Barrel Sponge

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Scientific Name: Xestospongia testudinaria

Species: Sponges (Petrosiidae)

Other names: Marine Sponges, Siliceous Sponges, Volcano Sponge, Giant Barrel Sponge, Great Vase Sponge

Description These gigantic sponges grow large enough to fit a person inside. Their hard surface is deeply ridged, but their rim is thin and delicate. The barrel sponge belongs to the Demospongiae, the largest class of sponges, containing about 95 percent of sponge species. The skeleton of sponges in this class is made from both scattered spicules of silica and organic collagen called spongin. An almost identical barrel sponge,Xestospongia muta, occurs in the Caribbean.

Habitat Found singly or in small groups on coral and rocky reef flats and reef faces.  Various creatures can often be found resting inside these sponges.  They feed on plankton.

Length – 1.5m

Depth - 10-30m

Commentary Sponges come in a range of sizes from minuscule encrusting species under rocks to massive sponges which can be up to one and half metres high.  They are able to filter many litres of sea water every few seconds.
Sponges can exude highly toxic chemicals and so have very few predators apart from nudibranchs, sea stars, sea urchins and umbrella shell.  Their colour can vary if growing in the light or when growing in the shade.

Features: The sponge is generally vase- or barrel-shaped, larger ones with a cavity in the centre. There are often finger-like bumps or ridges on the outside. Often several ‘vases’ of various sizes are found together emerging from what appears to be a common base. Those on the intertidal are about 10-20cm in diameter and about 10-20cm tall. But it is said that those found in deeper waters can grow to more than 1m tall. It is maroon to pinkish and the ‘opening’ of the barrel is paler to white.
Sponges are very complicated animals with very simple body plans.  They use millions of tiny flagellated cells both to move water through channels in their bodies and to capture bacteria-sized food particles.  They may build an internal skeleton of tiny glass needles or protein fibers, both of which help to prevent their bodies from being torn apart by currents.  Unlike any other animals, they don’t separate the inside of their bodies from the outside  – their tissue is an aggregation of cells, and among the sponge cells are often a diverse array of microorganisms, including photosynthetic blue-green bacteria, which give some of them a brownish coloration.

The spawning of the barrel sponges taking place two times per year is an incredible event that very few divers have seen.  This is when the sponges release a while substance and is seen by the naked eye and they implant this into the sponge to propagate.

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