Sea spongesPosted on September 25, 2018 - Last modified: September 25, 2018
The sea sponges shows Invertebrate animals y marine. They move very slowly along the seabed. Most move less than a millimeter a day, but some adult sponges are actually sessile, complaining that they are fixed to a rock or surface and remaining immobile. Adults lack a nervous system (such as the sea urchin) and defined musculature.
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It is estimated that sea sponges evolved around 500 million years ago, and there are currently more than 5.000 known and cataloged species but it is believed that there are still 5.000 new species to be discovered. Most sponges inhabit salt water and only the Spongillidae family inhabit fresh water.
Early naturalists classified sponges as aquatic plants, since they lack organs and not just move around like other animals do, but recent molecular studies suggest both that animals such as sponges evolved from a common ancestor.
The sponge has a body made of a gelatinous substance that is supported by a thin layer of cells on both sides. It lacks organs and is fed by the nutrients that enter through it since its is perforated.
They come in various sizes and shapes: tubes, fans, cups, cones, and globules. Most are only a few centimeters in size, but those that are urn-shaped or lacking are less than one centimeter and others that are shaped like vases, tubes, or branches are between one and two meters high and the more rounded species can have between one and two meters in diameter. The size of the species itself can vary as age advances, environmental conditions change and the food supply varies.
The external appearance varies, some are thick or tree-like with finger-shaped projections and others, particularly in the class particularly in the Demospongiae class, are amorphous masses that form fine inlays on objects or are cushion-shaped. Species of the class Demospongiae have well-defined more spherical shapes and others may have cup or fan shapes. Sponges of the genus Scypha are shaped like tubular sacs with an opening at the tip, and Hexactinellida members are fully erect or cylindrical with a pedicle base.
Like the appearance, the colors also vary. Very deep water sponges are neutral, gray or brown in color and shallow water sponges are brightly colored ranging from red, yellow, and orange to purple and black. Most sponges are calcareous, they are white in color but they get the color of the algae that live inside them in symbiosis. Those that are purple are those that contain symbiotic blue-green algae, however, when darkness arrives, they turn white since the photosynthesis that gives them the color does not take place.
The consistency of the sponge is also variable and can go from a white and viscous state of certain species adhering to the ground to the hard and stony quality of the Petrosia genus. The surface can be smooth, velvety, rough and provided with conical protrusions called conules.
Sponge life is unknown, small encrusted forms are probably one year old, and disappear during a season unfavorable for their survival; however, small fragments of an individual can persist and reproduce in the next season. Bath sponges (Hippospongia), for example, reach a commercially desirable size after seven years and can live up to 20 years.
Sponges inhabit all depths of the sea from the shallow tidal zone to the deepest regions (abysses). They can be found in all latitudes and are extremely numerous in Antarctic waters.
Light can limit their survival in certain habitats. Sponges that inhabit caves, shaded walls, or under small shelters like crevasses, inhabit the shoreline. However, some species in the tropics are only covered by one meter of water or less and are fully exposed to solar radiation. The symbiotic relationships between algae and sponges originate in very bright areas. Here the algae provide protection by pigmenting the sponge.
Sponges of the family Clionidae (class Demospongiae) that inhabit galleries that excavate in mollusk shells, corals, limestone and other calcareous materials through chemical and mechanical action.
Although most sponges settle and grow on hard or rocky surfaces, some will settle on a firm object on soft bottoms such as sand, mud, or debris. Loose sponges are rare.
Members of the Calcarea and Demospongiae families are located on the rocky bottoms of the continental shelf. The Hexactinellida family frequently inhabits the muddy bottoms of the oceans and seas.
In certain environments, they are the dominant organisms and cover large areas especially in rocky overhangs and in caves in the littoral or coastal zone.
Sponges are omnivorous animals that feed on the nutrients provided by water through its filtering system. They feed mainly on bacteria, phytoplankton and pieces of water. Some species have a more carnivorous diet, feeding on fish and small crustaceans on the reefs.
Sponges are prey for many animals because they move very slowly or do not move. In the case of being eaten they cannot avoid it. Its main predators are sea turtles, crustaceans, fish and echinoderms.
Sponges are hermaphroditic animals, that is, they have male and female reproductive organs. Although some are sequential hermaphrodites that have both genders but develop at different times in the animal's life. Most reproduce sexually, but some species reproduce asexually.
The sexual reproduction of a sponge is very particular. The fertilization of the ovule by the spermatozoon occurs when it is released from a sponge and carried by the current until it is captured by another sponge by a specialized flagellated cell called choanocyte or collar cell. The choanocyte transforms into an amoeba-shaped cell called a carrier cell that delivers sperm to an egg that is near a chamber made up of choanocytes and contains long, eyelash-shaped appendages called flagella.
Development occurs in various ways, depending on the different groups and the result is different types of larvae. The most common larval form among the Demospongiae is called the parenchyma; it is solid and compact, with an outer layer of flagellated cells and an inner mass of non-flagellated cells.
The larva must descend a few hours or a few days to locate a suitable surface for attachment. After mating, the larva metamorphose into a young sponge. This process implies change in its structure.
Sexual maturation is related to the temperature of the water in which they live. In temperate regions, they mature between spring and autumn, and sometimes there are two reproductive periods, one in spring and the other in autumn. Other species, for example Scypha, mature at any time of the year, as do tropical sponges. The vast majority of sponges are viiparous and the larvae are released through the channels, however, they can also be oviparous and lay eggs such as Cliona and Tethya.
Asexual reproduction in sponges takes place in a number of ways. The most used method is called gemulation. Gemulation consists of isolating archaeocytes by filling them with granules of reserve food and enveloping them with a protective layer. The gemmules are expelled from the adult sponge into the sea. It is normally used as a reproductive form but is sometimes used by family members as a means to transport sponges during unfavorable periods such as periods of drought or extreme temperatures.
In freshwater members of the Spongillidae family they have a distinct form of gemulation. The archaeocytes are not only filled with granules of reserve and protected food, but also the archaeocytes form protective membranes surrounding the gemmules. The protective covering is generally reinforced by spicules, which vary in shape according to the species and are useful in classification. Freshwater sponge gumules allow them to survive in unfavorable conditions in a state in which vital activities are almost suspended.
In colder regions, gemmulation occurs during winter and dormant gemmules are believed to hibernate. In hot regions, it occurs during the summer and gemmules are believed to be activated. When spring or fall return to the favorable conditions, the gemmules germinate and the archaeocytes emerge from the micropile (an opening) and a new sponge grows.
Other forms of asexual reproduction include the formation of stolons (root-like extensions) and the fragmentation of individuals as the starfish.
Sea sponges possess the extraordinary ability to regenerate not only in restoring damaged or lost parts, but they can also fully regenerate in an adult from small fragments or even individual cells. Cells have several methods of separating: mechanical or chemical.
Dissociated cells settle, migrate, and form active aggregates in which archaeocytes play an important role. In order for the small cell fragments to grow larger, the cells must adhere to a surface where they flatten and develop a special cell envelope (pinacocytes) called diamond. The choanocyte chambers and the channel system are then reconstituted, resulting in a young, functional and growing sponge.
Regeneration is not comparable to the embryonic process since the different types of dissociated cells participate in the formation of the new sponge by classifying and reorganizing, instead of differentiating from the primitive cell types. Sponge regeneration is of scientific interest in relation to cell-to-cell recognition, adhesion, sorting, movement, and properties of cells.
Under very unfavorable conditions the sponge may choose to fragment into small pieces of architects covered by layers of pinacocytes. When favorable conditions return they rejoin to form a complete sponge.
State of conservation
Although sponges are important to the environment, no assessment of their current global conservation status has yet been made. We found that most sponges do not appear to be globally threatened. However, little information is available on most species and more data is needed on the impacts of anthropogenic pressures.
Certain species of some families of sponges have been used by various cultures in the past for their soft and elastic skeletal structures such as species of the Demospongia class -for example, Spongia officinalis, Hippospongia communis, S. zimocca, S. graminea- for the use of familiar household items.
In ancient Greece and Rome they were used to apply paint, as mops, and as drinking glasses for soldiers. In the Middle Ages, the sponge was used for its therapeutic values and was used as a treatment for various diseases.
Today, sponges are used in art and crafts such as pottery and jewelry, painting and decoration, and in surgical medicine. For domestic use, natural sponges have been replaced by synthetic sponges.