Hexactinellid

The glass sponges ( Hexactinellida (Size: six-rayed ) ) are a class of the tribe of sponges ( Porifera ). The glass sponges include about 600 species that live exclusively in the sea, from the littoral to the deep sea (as of 2013). Glass sponges represent 8 % of all known species of sponges. They are currently in 19 families and 125 genera subdivided (World Porifera Database, 2013).

Glass sponges have in their skeleton on six-pointed needle or derivable forms of amorphous hydrated silica ( biogenic opal ) are constructed. The name of the class due to the morphology of their skeletal elements goes back to the zoologist Eduard Oscar Schmidt. In a Glasschwammart up to 20 different shaped needle types can occur. The glass sponges are fixed either to the base or to a bundle of long glass fibers to the substrate. An exception is the kind Monorhaphis chuni, which produces a single gigantic sponge nobility of up to 3 m in length and 8 mm in thickness, which is anchored in the deep-sea sponge bottom of the Indian and Pacific Oceans.

Hexactinellida are found in all oceans, they are (with few exceptions) deep-water fish. A particularly high density they reach the waters around the Antarctic continent at a depth of 100 to 500 m. Although they occur there only in a few species, they can account for up to 90 % of the sitting on the sea floor living organisms ( benthos ). The large glass sponges with numerous cavities in turn provide other invertebrate species, as well as juvenile fish, a living and protection facility. After the death of their sponges spicules remain lying on the ground and make the time up to 2m powerful glass wool-like needle mats that structure and change sea floor. Glass sponges are therefore an important ecological factor in the Antarctic.

The highest number of species in a limited region was counted with about 70 different species on the east coast of Japan in the Tokyo located in front of Sagami Bay. The presence of glass sponges from this region, at depths from 150 to 1000 m, have been known since the 30s of 19th century science. The type Hyalonema sieboldii, then still referred to as " glass plant" or " Glass Coral " was processed in ancient Japan to room decorations or hairpins.

Glass sponges are among the oldest multicellular animals of the earth's history. They were detected in about 545 million years old rock layers ( Ediacaran Formation, Upper Precambrian). Your highest spread they reached in the Upper Jurassic, about 200 million years ago, in the shallow waters of the Tethys. At this time, spanned a 7000 km long Schwammriff belt from today Caucasus, Romania, Southern Germany, the Iberian Peninsula up to the present coast of Newfoundland. Thus the Hexactinellida were significant Riffbildner, comparable to today's living coral. The limestone cliffs in the Franconian Alb, for example, fossil remains of such glass sponge reefs. The only known today more Glassschwammriff covers approximately 1,000 square kilometers off the west coast of Canada.

In Ostchinesichen sea a copy of Monoraphis chuni was found, who trained during his 11.000jährigen lifetime needles of 3 meters in length and 1 cm in thickness, which, annual rings serve ' as a climate archive and strongly fluctuating water temperatures ( 2-10 degrees C) show.

The mechanism of formation of the needle Hexactinellida is elucidated in its fundamentals. The needles are made of concentric layers deposited around a central hollow channel that fills an organic axial filament. This consists largely of a silicate - secreting enzyme silicatein named that belongs to the cathepsin subfamily. Another enzyme, the silicase, serves to keep the amorphous Si in solution. Silicase is related to the carbon anhydrases, active center is a metal complex with the participation of zinc. The finished needles coexist with the amorphous silicate glass mass, larger fractions of structural proteins, probably largely collagen. The " composite" of silicate glass and protein is more elastic than pure glass. Thus, it is possible to bend a sponge needle into circular shape; when released it returns back undamaged in their original form.

System

The glass sponges with about 500 known species can be divided into two sub-classes:

• Amphidiscophora
• Hexasterophora

Microscleres in the tissue of a glass sponge

The Japanese Hexactinellida researchers Isao Ijima (1861-1921) at his workplace surrounded by dry preparations of large glass sponges from the Sagami Bay

The glass sponge Chaunangium crater, captured on the Valdivia expedition in the years 1898-1899