Sponges are fascinating marine creatures with unique anatomy and physiology. These filter-feeding organisms lack true tissues but have specialized cells that perform vital functions. Their body structure includes a gelatinous matrix, outer and inner cell layers, and a skeleton of spicules or spongin fibers.
Sponges play crucial ecological roles in marine ecosystems. They provide habitat for other organisms, filter large volumes of water, and contribute to nutrient cycling. Some species even help maintain reef balance through bioerosion. Sponges also produce valuable secondary metabolites with potential pharmaceutical applications.
Sponge Anatomy and Physiology
Anatomy and physiology of marine sponges
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Asymmetrical, sessile, multicellular organisms that lack true tissues and organs but are composed of specialized cells with specific functions
Body structure consists of:
Mesohyl gelatinous matrix that fills the space between the external and internal cell layers
Pinacoderm outer cell layer made up of flattened pinacocyte cells that cover the exterior surface
Choanoderm inner cell layer composed of flagellated choanocyte (collar) cells lining the interior canals and chambers that beat flagella to create water currents for filter feeding
Skeleton composed of spicules (siliceous or calcareous) that provide structural support and defense against predators and/or spongin flexible protein fibers that form the sponge skeleton
Canal system includes:
Ostia tiny pores on the surface that allow water to enter the sponge
Incurrent canals that transport water from the ostia to the choanocyte chambers
Choanocyte chambers spaces lined with that filter food particles from the water
Excurrent canals that transport filtered water out of the sponge
Oscula large openings where filtered water exits the sponge
Feeding and reproduction of sponges
Filter feeders that obtain food by filtering water through their bodies using choanocytes to create water currents and trap food particles like bacteria, phytoplankton, and dissolved organic matter which are then digested by pinacocytes and amoebocytes and nutrients distributed
Reproduce asexually through:
Budding where new individuals grow from the parent sponge and detach
Gemmules resistant structures containing totipotent cells that survive unfavorable conditions and develop into new sponges
Regeneration where sponges can regrow from small fragments
Reproduce sexually as hermaphroditic organisms that produce both sperm and eggs
Oviparous eggs are fertilized internally and larvae are released into the water column
Viviparous eggs are fertilized and develop into larvae within the parent sponge
Larval stage planktonic larvae disperse before settling and metamorphosing into adult sponges
Ecological roles of marine sponges
Provide habitat and shelter for various organisms like crustaceans, worms, and echinoderms and contribute to the formation of coral reefs and other benthic communities
Filter large volumes of water, removing particulate matter and dissolved organic carbon, playing a crucial role in coupling benthic and pelagic environments and contributing to nutrient cycling by converting suspended particles into food for other organisms
Some species bore into coral skeletons and calcareous substrates through bioerosion, helping maintain the balance between reef growth and erosion
Host diverse microbial communities within their tissues in symbiotic relationships that contribute to sponge metabolism and chemical defense
Produce a wide array of secondary metabolites with biotechnological potential for pharmaceutical and biomedical applications with antiviral, antibacterial, antifungal, and anticancer properties
Classes of marine sponges
Calcarea (calcareous sponges) have a skeleton composed of calcium carbonate spicules, are exclusively marine, have simple leuconoid or syconoid canal systems (Sycon, Leucosolenia)
Hexactinellida (glass sponges) have a skeleton composed of siliceous spicules with a triaxonic (six-rayed) symmetry, are mainly deep-sea inhabitants, have syncytial tissue organization (Euplectella/Venus' flower basket, Aphrocallistes)
Demospongiae () are the largest and most diverse of sponges with a skeleton composed of siliceous spicules and/or spongin fibers, have a leuconoid canal system, and diverse morphologies and adaptations (Aplysina/Yellow tube sponge, Cliona/Boring sponge, Xestospongia/Giant barrel sponge)
Homoscleromorpha have a skeleton composed of siliceous spicules with a tetraxonic (four-rayed) symmetry, a simple canal system, and cellular organization similar to other metazoans (Oscarella, Plakina)