Sclerocyte

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Sclerocytes are specialised cells that secrete the mineralized structures in the body wall of some invertebrates.

In sponges they secrete calcareous or siliceous spicules which are found in the mesohyl layer of sponges. The sclerocytes produce spicules via formation of a cellular triad. The triad of cells then undergo mitosis, creating six sclerocytes. In pairs, the sclerocytes secrete the minerals which create the spicules. [1]

In starfish they are present in the dermis and secrete the calcite microcrystals from which the ossicles are formed. They also function in growth and repair of the ossicles. [2]

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<span class="mw-page-title-main">Skeleton</span> Part of the body that forms the supporting structure

A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside the body, and the hydroskeleton, a flexible internal skeleton supported by fluid pressure. Vertebrates are animals with a vertebral column, and their skeletons are typically composed of bone and cartilage. Invertebrates are animals that lack a vertebral column. The skeletons of invertebrates vary, including hard exoskeleton shells, plated endoskeletons, or spicules. Cartilage is a rigid connective tissue that is found in the skeletal systems of vertebrates and invertebrates.

<span class="mw-page-title-main">Sponge</span> Animals of the phylum Porifera

Sponges, the members of the phylum Porifera, are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells.

<span class="mw-page-title-main">Hexactinellid</span> Class of sponges with siliceous spicules

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. Some experts believe glass sponges are the longest-lived animals on earth; these scientists tentatively estimate a maximum age of up to 15,000 years.

Spicules are any of various small needle-like anatomical structures occurring in organisms

<span class="mw-page-title-main">Calcareous sponge</span> Class of marine sponges of the phylum Porifera which have spicules of calcium carbonate

The calcareoussponges are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate, in the form of high-magnesium calcite or aragonite. While the spicules in most species are triradiate, some species may possess two- or four-pointed spicules. Unlike other sponges, calcareans lack microscleres, tiny spicules which reinforce the flesh. In addition, their spicules develop from the outside-in, mineralizing within a hollow organic sheath.

<span class="mw-page-title-main">Choanocyte</span>

Choanocytes are cells that line the interior of asconoid, syconoid and leuconoid body types of sponges that contain a central flagellum, or cilium, surrounded by a collar of microvilli which are connected by a thin membrane.

<span class="mw-page-title-main">Osteoblast</span> Cells secreting extracellular matrix

Osteoblasts are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.

<span class="mw-page-title-main">Osteocyte</span> Mature osteoblasts which helps in communication between cells and also in molecular synthesis

An osteocyte, an oblate shaped type of bone cell with dendritic processes, is the most commonly found cell in mature bone. It can live as long as the organism itself. The adult human body has about 42 billion of them. Osteocytes do not divide and have an average half life of 25 years. They are derived from osteoprogenitor cells, some of which differentiate into active osteoblasts. Osteoblasts/osteocytes develop in mesenchyme.

<span class="mw-page-title-main">Intramembranous ossification</span> Mesenchymal bone development that forms the non-long bones

Intramembranous ossification is one of the two essential processes during fetal development of the gnathostome skeletal system by which rudimentary bone tissue is created. Intramembranous ossification is also an essential process during the natural healing of bone fractures and the rudimentary formation of bones of the head.

<span class="mw-page-title-main">Demosponge</span> Class of sponges

Demosponges (Demospongiae) are the most diverse class in the phylum Porifera. They include 76.2% of all species of sponges with nearly 8,800 species worldwide. They are sponges with a soft body that covers a hard, often massive skeleton made of calcium carbonate, either aragonite or calcite. They are predominantly leuconoid in structure. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges. Some species, in particular from the Antarctic, obtain the silica for spicule building from the ingestion of siliceous diatoms.

The mesohyl, formerly known as mesenchyme or as mesoglea, is the gelatinous matrix within a sponge. It fills the space between the external pinacoderm and the internal choanoderm. The mesohyl resembles a type of connective tissue and contains several amoeboid cells such as amebocytes, as well as fibrils and skeletal elements. For a long time, it has been largely accepted that sponges lack true tissue, but it is currently debated as to whether mesohyl and pinacoderm layers are tissues.

<i>Suberites domuncula</i> Species of sponge

Suberites domuncula is a species of sea sponge belonging to the family Suberitidae.

Archaeocytes or amoebocytes are amoeboid cells found in sponges. They are totipotent and have varied functions depending on the species. The structure of these cells match to that of the stem cells as of containing high cytoplasmic content that helps the cells to morph according to their function.

<i>Anheteromeyenia argyrosperma</i> Species of sponge

Anheteromeyenia argyrosperma is a freshwater sponge found across North America.

<span class="mw-page-title-main">Sponge spicule</span> Structural element of sea sponges

Spicules are structural elements found in most sponges. The meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators.

<i>Suberites</i> Genus of sponges

Suberites is a genus of sea sponges in the family Suberitidae. Sponges, known scientifically as Porifera, are the oldest metazoans and are used to elucidate the basics of multicellular evolution. These living fossils are ideal for studying the principal features of metazoans, such as extracellular matrix interactions, signal-receptor systems, nervous or sensory systems, and primitive immune systems. Thus, sponges are useful tools with which to study early animal evolution. They appeared approximately 580 million years ago, in the Ediacaran.

<i>Spiculosiphon oceana</i> Species of single-celled organism

Spiculosiphon oceana is a giant species of foraminifera. Its appearance and lifestyle mimics that of a sponge. It was discovered in 2013 in underwater caves 30 miles off the coast of Spain.

<span class="mw-page-title-main">Precambrian body plans</span> Structure and development of early multicellular organisms

Until the late 1950s, the Precambrian was not believed to have hosted multicellular organisms. However, with radiometric dating techniques, it has been found that fossils initially found in the Ediacara Hills in Southern Australia date back to the late Precambrian. These fossils are body impressions of organisms shaped like disks, fronds and some with ribbon patterns that were most likely tentacles.

<span class="mw-page-title-main">Silicatein</span>

Silicateins are enzymes which catalyse the formation of biosilica from monomeric silicon compounds extracted from the natural environment. Environmental silicates are absorbed by specific biota, including diatoms, radiolaria, silicoflagellates, and siliceous sponges; silicateins have so far only been found in sponges. Silicateins are homologous to the cysteine protease cathepsin.

Oopsacas minuta is a glass sponge that is a member of the Hexactinellida. Oopsacas minuta is found in submarine caves in the Mediterranean. It is reproductive year-round. This species is a part of a class that are usually bathyal and abyssal. Meaning they grow at a depth over 200 meters. At this depth the temperature is low and constant, so silica metabolism is optimized. However, this species has been observed in shallow water. O. minuta have only been observed by exploring caves that trap cold water. The shape of the sponge is elongated, cylindrical and a little flared. It is between a few millimeters and 3.5 centimeters. O. minuta are white are held up with a siliceous skeleton. The spicules of the skeleton intersect in an intricate network. These spindles partially block the top of the sponge. There are no obvious oscules. The sponge is anchored or suspended from the cave by silica fibers. This class of sponge is different from the three other classes of Porifera. It differs in tissue organization, ecology, development and physiology. O. minuta belongs to the order Lyssacinosida. Lyssacinosida are characterized by the parenchymal spicules mostly being unconnected; this is unlike other sponges in the subclass where the spicules form a connected skeleton. The genome of O. minuta are one of the smallest of all the animal genomes that have been sequenced so far. Its genome contains 24 noncoding genes and 14 protein-encoding genes. The spindles of O. minuta have three axes and six points. This species does not have pinacocytes, which are the cells that form the outer layer in other sponges. Instead of true choanocytes it has frill structures that bud from the syncytium.

References

  1. Imsiecke, Georg; Steffen, Renate; Custodio, Marcio; Borojevic, Radovan; Muller, Werner E. G. (1995). "Formation of spicules by sclerocytes from the freshwater sponge Ephydatia muelleri in short-trem cultures in vitro" (PDF). In Vitro Cellular & Developmental Biology - Animal. 31 (7): 528–535. doi:10.1007/BF02634030. PMID   8528501. S2CID   22067910.
  2. Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 875. ISBN   81-315-0104-3.