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More commonly, the mesohyl is stiffened by mineral spicules, by spongin fibers, or both. 90% of all known sponge species that have the widest range of habitats including all freshwater ones are demosponges that use spongin; many species have silica spicules, whereas some species have calcium carbonate exoskeletons. Calcareous sponges have ...
Tetraxons have four axes, and polyaxons more (description of types to be incorporated from [31]). Sigma-C spicules have the shape of a C. [31] Dendroclones might be unique to extinct sponges [32] and are branching spicules that may take irregular forms, or may form structures with an I, Y or X shape. [33] [34]
About 311 million years ago, in the Late Carboniferous, the order Spongillida split from the marine sponges, and is the only sponges to live in freshwater environments. [7] Some species are brightly colored, with great variety in body shape; the largest species are over 1 m (3.3 ft) across. [ 5 ]
Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding 8,800 m (5.5 mi).
A true endoskeleton is derived from mesodermal tissue. In three phyla of animals, Chordata, Echinodermata and Porifera (), endoskeletons of various complexity are found.An endoskeleton may function purely for structural support (as in the case of Porifera), but often also serves as an attachment site for muscles and a mechanism for transmitting muscular forces as in chordates and echinoderms ...
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The calcareous sponges [2] [3] (class Calcarea) are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate, in the form of high-magnesium calcite or aragonite. While the spicules in most species are triradiate (with three points in a single plane), some species may possess two ...