sponge

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Figure 33: (Top) A colony of three species of sponges, approximately three-quarters of life size. At top of colony is a small bread-crumb sponge (Halichondria); branching mass at right is leucosolenia complicata; tubular sponges on left are Scypha cilia

(Top) Spongia, (centre) Hippospongia communis, and (bottom) Spongia

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A simple saclike sponge. Its surface is perforated by small openings (incurrent pores) formed by tubelike cells (porocytes), which open into the internal cavity. A gelatinous middle layer contains the skeletal elements (spicules and spongin fibers) as well as amebocytes active in digestion, waste removal, and spicule and spongin formation. Flagellated collar cells (choanocytes) line the internal cavity, create currents to move water containing oxygen and food into the sponge, and engulf and digest food particles. Water and wastes are expelled through the ostium opening, whose size can be altered to regulate water flow through the sponge.

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sponge

animal

Also known as: Porifera, poriferan

Written by Michele Sarà

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Dec 20, 2024 • Article History

Key People:: James Scott Bowerbank

Related Topics:: archaeocyathid; siliceous sponge; calcareous sponge; glass sponge; Axinella

On the Web:: Mustansiriyah University - Phylum: Porifera (Sponges) (PDF) (Dec. 20, 2024)

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sponge, any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more. The members of one family, the Spongillidae, are found in fresh water; however, 98 percent of all sponge species are marine. Adult sponges lack a definite nervous system and musculature and do not show conspicuous movements of body parts. Early naturalists regarded the sponges as plants because of their frequent branching form and their lack of obvious movement. ...(100 of 6824 words)

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