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Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella. [13]: 29 However, a few carnivorous sponges have lost these water flow systems and the choanocytes.
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. [8] Some species are brightly colored, with great variety in body shape; the largest species are over 1 m (3.3 ft) across. [ 6 ]
All sponges in this class are strictly marine, and, while they are distributed worldwide, most are found in shallow tropical waters. Like nearly all other sponges, they are sedentary filter feeders. All three sponge body plans (asconoid, syconoid, and leuconoid) can be found within the class Calcarea. Typically, calcareous sponges are small ...
Most aspects of sponge biology, including feeding, reproduction, and gas exchange, depend on a low pressure flow of water generated by the flagella of the choanoderm. Three grades of organization, asconoid, syconoid, and leuconoid, reflect the degree of elaboration of the choanoderm layer and mesohyl.
Sponges are hermaphrodites, producing both egg and sperm. Sperm is released from one sponge and brought in through the ostia of another sponge. Once the sperm reaches the body cavity it is fertilized and develops into a free-swimming larvae. The free-swimming larvae are released out the osculum and will eventually settle and attach elsewhere. [6]
The algae help facilitate oxygen and food uptake for the sponge, while the sponge provides the algae a surface to live on. The gemmules of Spongilla lacustris inside the original parent sponge. The texture of the sponge itself is soft. The ostia (dermal pores) let water into the sponge to be filtered. The oscula is the hole from which water exits.
Drawing of a choanoflagellate colony by Metchnikoff, 1886. Over 125 extant species of choanoflagellates [12] are known, distributed globally in marine, brackish and freshwater environments from the Arctic to the tropics, occupying both pelagic and benthic zones.
Flow tank experiments suggest that archaeocyathan morphology allowed them to exploit flow gradients, either by passively pumping water through the skeleton, or, as in present-day, extant sponges, by drawing water through the pores, removing nutrients, and expelling spent water and wastes through the pores into the central space.