Asexual reproduction is infrequent and includes regeneration, budding, fragmentation, and gemmule formation. Regeneration is the ability of a new individual to develop from a detached part of another individual. Regeneration also enables sponges to repair and replace damaged or severed body parts. In budding, a new individual grows out of the body of the sponge. The new developing sponge may remain attached to or separate from the body of the parent sponge. In fragmentation, new sponges develop from pieces that have fragmented from the body of the parent sponge. Sponges may also produce a specialized mass of cells with a hard outer covering (gemmule) that can be released and develop into a new sponge. Gemmules are produced under harsh environmental conditions to enable survival until conditions become favorable again.
Glass Sponges
Glass Sponges
NOAA Okeanos Explorer Program, Gulf of Mexico 2012 Expedition
Glass sponges of the class Hexactinellida typically live in deep sea environments and may also be found in Antarctic regions. Most hexactinellids exhibit radial symmetry and commonly appear pale with regard to color and cylindrical in form. Most are vase-shaped, tube-shaped, or basket-shaped with leuconoid body structure. Glass sponges range in size from a few centimeters in length to 3 meters (almost 10 feet) in length.
The hexactinellid skeleton is constructed of spicules composed entirely of silicates. These spicules are often arranged into a fused network that gives the appearance of a woven, basket-like structure. It is this mesh-like form that gives hexactinellids the firmness and strength required to live at depths of 25 to 8,500 meters (80–29,000 feet). Tissue-like material also containing silicates overlays the spicule structure forming thin fibers that cling to the framework.
The most familiar representative of the glass sponges is the Venus' flower-basket. A number of animals use these sponges for shelter and protection including shrimp. A male and female shrimp pair will take up residence in the flower-basket house when they are young and continue to grow until they are too large to leave the confines of the sponge. When the couple reproduces young, the offspring are small enough to leave the sponge and find a new Venus' flower-basket. The relationship between the shrimp and the sponge is one of mutualism as both receive benefits. In return for protection and food provided by the sponge, the shrimp help to keep the sponge clean by removing debris from the sponge's body.
Calcarious Sponges
Calcareous Yellow Sponge
Wolfgang Poelzer/WaterFrame/Getty Images
Calcareous sponges of the class Calcarea commonly reside in tropical marine environments at more shallow regions than glass sponges. This class of sponges has fewer known species than Hexactinellida or Demospongiae with around 400 identified species. Calcareous sponges have varied shapes including tube-like, vase-like, and irregular shapes. These sponges are usually small (a few inches in height) and some are brightly colored. Calcareous sponges are characterized by a skeleton formed from calcium carbonate spicules. They are the only class to have species with asconoid, syconoid, and leuconoid forms.
Demosponges
Tube Sponge
Jeffrey L. Rotman/Corbis Documentary/Getty Images
Demosponges of the class Demospongiae are the most numerous of the sponges containing 90 to 95 percent of Porifera species. They are typically brightly colored and range in size from a few millimeters to several meters. Demosponges are asymmetrical forming a variety of shapes including tube-like, cup-like, and branched shapes. Like glass sponges, they have leuconoid body forms. Demosponges are characterized by skeletons with spicules composed of collagen fibers called spongin. It is the spongin that gives sponges of this class their flexibility. Some species have spicules that are composed of silicates or both spongin and silicates.
Placozoa Parazoa
Placozoa
Eitel M, Osigus H-J, DeSalle R, Schierwater B (2013) Global Diversity of the Placozoa. PLoS ONE 8(4): e57131. doi:10.1371/journal.pone.0057131
Parazoa of the phylum Placozoa contains only one known living species Trichoplax adhaerens. A second species, Treptoplax reptans, has not been observed in more than 100 years. Placozoans are very tiny animals, about 0.5 mm in diameter. T. adhaerens was first discovered creeping along the sides of an aquarium in an amoeba-like fashion. It is asymmetrical, flat, covered with cilia, and able to adhere to surfaces. T. adhaerens has a very simple body structure that is organized into three layers. An upper cell layer provides protection for the organism, a middle meshwork of connected cells enable movement and shape change, and a lower cell layer functions in nutrient acquisition and digestion. Placozoans are capable of both sexual and asexual reproduction. They reproduce primarily by asexual reproduction through binary fission or budding. Sexual reproduction occurs typically during times of stress, such as during extreme temperature changes and low food supply.
Theory of everything
We do not have a theory of everything. It is a hope for the future. The basic concept of the theory of everything is that one theory could explain every aspect of physics. The four basic forces of nature are gravity, the strong force, the weak force, and the electromagnetic force; the theory of general relativity explains gravity, and quantum mechanics explains the other three forces. Right now, no one theory that everyone accepts can explain all four forces.
String theory is a theory that could become the "theory of everything".
Unified field theory is a hope for a theory of fields in physics that will explain all natural phenomena. Theories in physics can be very different and even disagree with each other. This is true for example for quantum mechanics (the science of very small things) and general relativity (the science of space and time). The goal of unified field theory is to take all the different parts of physics and combine them into one theory that explains everything. The Standard Model comes close to a unified field theory, combining everything except general relativity.
Dichotomous key
A dichotomous key is a series of questions with only two alternatives. There are only two options at each step. The purpose is to make an identification or to reach a decision. The system has long been used for identifying animals and plants. However, in principle, it can be used for many other tasks, such as fault-finding in complex machinery.
KISS (principle)
The KISS principle is "Keep It Simple, Stupid". It is an acronym, with the letters KISS making the beginnings of the important words. It was used as a principle for design by the U.S. Navy in 1960. The phrase is said to have been first used by Kelly Johnson, lead engineer at the Lockheed Skunk Works.
There are several variations of the phrase, such as "Keep it short and simple".
Linguistic reduction
Linguistic reductions are lost sounds in words, which happens in spoken English. For instance, "going to" changes to "gonna". The most common reductions are contractions. Most contractions are reductions of 'not'. For instance, "cannot" becomes "can't". Many contractions are reductions between a subject and a verb. For instance, "He is..." becomes "He's..."
Some reductions are known to language learners, such as the reduction of a verb and "to". Examples are "going to" becoming "gonna" and "want to" becoming "wanna".
Linguistic reductions are part of natural English and should not be considered slang or improper.
There are several basic categories of reductions:
Tokyo Metro
The is one of two rapid transit systems making up the Tokyo subway system, the other being Toei.
"Note:" Including the 8.3 km stretch between Wakoshi and Kotake-mukaihara shared with Yurakucho Line.
Glomma
Glomma is the longest river in Norway. It is long and runs from Aursund to Fredrikstad.
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