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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.
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]
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.
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 three sponge body plans (asconoid, syconoid, and leuconoid) can be found within the class Calcarea. Typically, calcareous sponges are small, measuring less than 10 cm (3.9 in) in height, and drab in colour. However, a few brightly coloured species are also known. Like the Homoscleromorpha, calcareous sponges are exclusively viviparous. [7]
The cells in the sponge walls filter food from the water. Whatever is not uptaken by the sponge is pumped through the body out of a large opening. The class demosponges are the most abundant and diverse of the sponge classes. Some of the sponges in this class have skeletons made from silicon-containing spicules, spongin fibers, or both ...
Kalymnos was the main centre of sponge production in the Aegean, and sponge diving is still a traditional albeit less common occupation of the Greeks on the island, with related exhibitions, along with other local folklore, and three museums about the occupation. 1897 schematic of commercial sponge diving
Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed siliceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera , but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma .