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Hexactinellids make up a very small part of the phylum Porifera. Their most distinguishing feature is their four and six-pointed spicules made primarily of silica. They are often cup-shaped, and can be found almost exclusively in very deep waters. They are similar to demosponges as fossils, but this may be because their structure is much stronger than spongin fiber and holds up better after fossilization.
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