hexactinellida

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A JURASSIC PARK OF SPONGE IN THE MEDITERRANEAN SEA

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.

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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.

Phylogeny

Animalia-Porifera-Hexactinellida-Hexasterophora-Hexactinosida-Aphrocallistidae-Aphrocallistes-vastus

Image Source(s)

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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 ARE GLASS SPONGE MADE BY GLASS?

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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