Sponge

This is a good article. Click here for more information.
Page semi-protected
Source: Wikipedia, the free encyclopedia.
(Redirected from
Sponges
)

Sponges
Temporal range: Ediacaran–recent
A stove-pipe sponge
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Porifera
Grant
, 1836
Classes
Synonyms

Parazoa/Ahistozoa (sans Placozoa)[1]

Sponges (also known as sea sponges), the members of the

basal animal clade as a sister of the diploblasts.[2][3][4][5][6] 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
.

Sponges have unspecialized cells that can

evolutionary tree from the last common ancestor of all animals, which would make them the sister group of all other animals.[2]

Etymology

The term sponge derives from the Ancient Greek word σπόγγος (spóngos 'sponge').[8]

Overview

morphotypes at the lip of a wall site in 60 feet (20 m) of water. Included are the yellow tube sponge, Aplysina fistularis, the purple vase sponge, Niphates digitalis, the red encrusting sponge, Spirastrella coccinea, and the gray rope sponge, Callyspongia
sp.

Sponges are similar to other animals in that they are

larval stage of life they are motile
. Although there are freshwater species, the great majority are marine (salt-water) species, ranging in habitat from tidal zones to depths exceeding 8,800 m (5.5 mi).

Although most of the approximately 5,000–10,000 known species of sponges feed on bacteria and other microscopic food in the water, some host photosynthesizing microorganisms as endosymbionts, and these alliances often produce more food and oxygen than they consume. A few species of sponges that live in food-poor environments have evolved as carnivores that prey mainly on small crustaceans.[11]

Sponges reproduce both asexually and sexually. Most species that use

ova that in some species are released and in others are retained by the "mother". The fertilized eggs develop into larvae, which swim off in search of places to settle.[12] Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. Some species reproduce by budding. When environmental conditions become less hospitable to the sponges, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules, "survival pods" of unspecialized cells that remain dormant until conditions improve; they then either form completely new sponges or recolonize the skeletons of their parents.[13]

In most sponges, an internal gelatinous matrix called mesohyl functions as an

Archaeocyathids, whose fossils are common in rocks from 530 to 490
million years ago, are now regarded as a type of sponge.

flagella draws water through the sponge so that nutrients can be extracted and waste removed.[15]

The

single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with phylogenetic studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals.[16]

The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools. By the 1950s, though, these had been overfished so heavily that the industry almost collapsed, and most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. Dolphins have been observed using sponges as tools while foraging.[17]

Distinguishing features

Sponges constitute the

metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella.[18] However, a few carnivorous sponges have lost these water flow systems and the choanocytes.[19][20] All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another.[20][21]

Even if a few sponges are able to produce mucus – which acts as a microbial barrier in all other animals – no sponge with the ability to secrete a functional mucus layer has been recorded. Without such a mucus layer their living tissue is covered by a layer of microbial symbionts, which can contribute up to 40–50% of the sponge wet mass. This inability to prevent microbes from penetrating their porous tissue could be a major reason why they have never evolved a more complex anatomy.[22]

Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of a non-living jelly-like mass (mesohyl) sandwiched between two main layers of cells.[23][24] Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina").[24] Sponges do not have a nervous system similar to that of vertebrates but may have one that is quite different.[7] Their middle jelly-like layers have large and varied populations of cells, and some types of cells in their outer layers may move into the middle layer and change their functions.[21]

  Sponges[21][23]
ctenophores[24]
Nervous system No/Yes Yes, simple
Cells in each layer bound together No, except that
Homoscleromorpha have basement membranes.[25]
Yes: inter-cell connections; basement membranes
Number of cells in middle "jelly" layer Many Few
Cells in outer layers can move inwards and change functions Yes No

Basic structure

Cell types

    Mesohyl
    Pinacocyte
    Choanocyte
    Lophocyte
    Porocyte
    Oocyte
   
Archeocyte
    Sclerocyte
   
Spicule
    Water flow
Main cell types of Porifera[26]

A sponge's body is hollow and is held in shape by the

porocytes that form closable inlet valves. Pinacocytes, plate-like cells, form a single-layered external skin over all other parts of the mesohyl that are not covered by choanocytes, and the pinacocytes also digest food particles that are too large to enter the ostia,[21][23] while those at the base of the animal are responsible for anchoring it.[23]

Other types of cells live and move within the mesohyl:[21][23]

  • Lophocytes are amoeba-like cells that move slowly through the mesohyl and secrete collagen fibres.
  • Collencytes are another type of collagen-producing cell.
  • Rhabdiferous cells secrete polysaccharides that also form part of the mesohyl.
  • Oocytes and spermatocytes are reproductive cells.
  • Sclerocytes secrete the mineralized spicules ("little spines") that form the skeletons of many sponges and in some species provide some defense against predators.
  • In addition to or instead of sclerocytes, demosponges have spongocytes that secrete a form of collagen that polymerizes into spongin, a thick fibrous material that stiffens the mesohyl.
  • Myocytes
    ("muscle cells") conduct signals and cause parts of the animal to contract.
  • "Grey cells" act as sponges' equivalent of an immune system.
  • totipotent
    , in other words, each is capable of transformation into any other type of cell. They also have important roles in feeding and in clearing debris that block the ostia.

Many larval sponges possess neuron-less eyes that are based on cryptochromes. They mediate phototaxic behavior.[28]

Glass sponges' syncytia

syncitium
and collar bodies showing interior

silica, form a scaffolding-like framework between whose rods the living tissue is suspended like a cobweb that contains most of the cell types.[21] This tissue is a syncytium that in some ways behaves like many cells that share a single external membrane, and in others like a single cell with multiple nuclei. The mesohyl is absent or minimal. The syncytium's cytoplasm, the soupy fluid that fills the interiors of cells, is organized into "rivers" that transport nuclei, organelles ("organs" within cells) and other substances.[30] Instead of choanocytes, they have further syncytia, known as choanosyncytia, which form bell-shaped chambers where water enters via perforations. The insides of these chambers are lined with "collar bodies", each consisting of a collar and flagellum but without a nucleus of its own. The motion of the flagella sucks water through passages in the "cobweb" and expels it via the open ends of the bell-shaped chambers.[21]

Some types of cells have a single nucleus and membrane each but are connected to other single-nucleus cells and to the main syncytium by "bridges" made of cytoplasm. The sclerocytes that build spicules have multiple nuclei, and in glass sponge larvae they are connected to other tissues by cytoplasm bridges; such connections between sclerocytes have not so far been found in adults, but this may simply reflect the difficulty of investigating such small-scale features. The bridges are controlled by "plugged junctions" that apparently permit some substances to pass while blocking others.[30]

Water flow and body structures

Asconoid
Syconoid
Leuconoid
    Mesohyl
    Water flow
Porifera body structures[31]

Most sponges work rather like chimneys: they take in water at the bottom and eject it from the osculum ("little mouth") at the top. Since ambient currents are faster at the top, the suction effect that they produce by Bernoulli's principle does some of the work for free. Sponges can control the water flow by various combinations of wholly or partially closing the osculum and ostia (the intake pores) and varying the beat of the flagella, and may shut it down if there is a lot of sand or silt in the water.[21]

Although the layers of

epithelia of more complex animals, they are not bound tightly by cell-to-cell connections or a basal lamina (thin fibrous sheet underneath). The flexibility of these layers and re-modeling of the mesohyl by lophocytes allow the animals to adjust their shapes throughout their lives to take maximum advantage of local water currents.[32]

The simplest body structure in sponges is a tube or vase shape known as "asconoid", but this severely limits the size of the animal. The body structure is characterized by a stalk-like spongocoel surrounded by a single layer of choanocytes. If it is simply scaled up, the ratio of its volume to surface area increases, because surface increases as the square of length or width while volume increases proportionally to the cube. The amount of tissue that needs food and oxygen is determined by the volume, but the pumping capacity that supplies food and oxygen depends on the area covered by choanocytes. Asconoid sponges seldom exceed 1 mm (0.039 in) in diameter.[21]

Diagram of a syconoid sponge

Some sponges overcome this limitation by adopting the "syconoid" structure, in which the body wall is pleated. The inner pockets of the pleats are lined with choanocytes, which connect to the outer pockets of the pleats by ostia. This increase in the number of choanocytes and hence in pumping capacity enables syconoid sponges to grow up to a few centimeters in diameter.

The "leuconoid" pattern boosts pumping capacity further by filling the interior almost completely with mesohyl that contains a network of chambers lined with choanocytes and connected to each other and to the water intakes and outlet by tubes. Leuconid sponges grow to over 1 m (3.3 ft) in diameter, and the fact that growth in any direction increases the number of choanocyte chambers enables them to take a wider range of forms, for example, "encrusting" sponges whose shapes follow those of the surfaces to which they attach. All freshwater and most shallow-water marine sponges have leuconid bodies. The networks of water passages in

glass sponges are similar to the leuconid structure.[21]
In all three types of structure the cross-section area of the choanocyte-lined regions is much greater than that of the intake and outlet channels. This makes the flow slower near the choanocytes and thus makes it easier for them to trap food particles.[21] For example, in Leuconia, a small leuconoid sponge about 10 centimetres (3.9 in) tall and 1 centimetre (0.39 in) in diameter, water enters each of more than 80,000 intake canals at 6 cm per minute. However, because Leuconia has more than 2 million flagellated chambers whose combined diameter is much greater than that of the canals, water flow through chambers slows to 3.6 cm per hour, making it easy for choanocytes to capture food. All the water is expelled through a single osculum at about 8.5 cm per second, fast enough to carry waste products some distance away.[33]

Archeocytes and other cells in mesohyl
  •   Mesohyl
  •   Spicules
  • Skeleton

    In zoology a

    silica or calcium carbonate, and vary in shape from simple rods to three-dimensional "stars" with up to six rays. Spicules are produced by sclerocyte cells,[21] and may be separate, connected by joints, or fused.[20]

    Some sponges also secrete

    sclerosponges ("hard sponges") have massive calcium carbonate exoskeletons over which the organic matter forms a thin layer with choanocyte chambers in pits in the mineral. These exoskeletons are secreted by the pinacocytes that form the animals' skins.[21]

    Vital functions

    Spongia officinalis, "the kitchen sponge", is dark grey when alive.

    Movement

    Although adult sponges are fundamentally

    sessile animals, some marine and freshwater species can move across the sea bed at speeds of 1–4 mm (0.039–0.157 in) per day, as a result of amoeba-like movements of pinacocytes and other cells. A few species can contract their whole bodies, and many can close their oscula and ostia. Juveniles drift or swim freely, while adults are stationary.[21]

    Respiration, feeding and excretion

    glass sponge
    known as "Venus' flower basket"

    Sponges do not have distinct

    vesicles from cells that directly digest food to those that do not. At least one species of sponge has internal fibers that function as tracks for use by nutrient-carrying archaeocytes,[21] and these tracks also move inert objects.[23]

    It used to be claimed that

    glass sponges could live on nutrients dissolved in sea water and were very averse to silt.[36] However, a study in 2007 found no evidence of this and concluded that they extract bacteria and other micro-organisms from water very efficiently (about 79%) and process suspended sediment grains to extract such prey.[37] Collar bodies digest food and distribute it wrapped in vesicles that are transported by dynein "motor" molecules along bundles of microtubules that run throughout the syncytium.[21]

    Sponges' cells absorb oxygen by diffusion from water into cells as water flows through body, into which carbon dioxide and other soluble waste products such as ammonia also diffuse. Archeocytes remove mineral particles that threaten to block the ostia, transport them through the mesohyl and generally dump them into the outgoing water current, although some species incorporate them into their skeletons.[21]

    Carnivorous sponges

    The carnivorous ping-pong tree sponge, Chondrocladia lampadiglobus[38]

    In waters where the supply of food particles is very poor, some species prey on

    filter-feeding sponges. The cave-dwelling predators capture crustaceans under 1 mm (0.039 in) long by entangling them with fine threads, digest them by enveloping them with further threads over the course of a few days, and then return to their normal shape; there is no evidence that they use venom.[42]

    Most known carnivorous sponges have completely lost the water flow system and choanocytes. However, the genus Chondrocladia uses a highly modified water flow system to inflate balloon-like structures that are used for capturing prey.[40][43]

    Endosymbionts

    Freshwater sponges often host

    silica conduct light into the mesohyl, where the photosynthesizing endosymbionts live.[44] Sponges that host photosynthesizing organisms are most common in waters with relatively poor supplies of food particles and often have leafy shapes that maximize the amount of sunlight they collect.[23]

    A recently discovered carnivorous sponge that lives near

    methane-eating bacteria and digests some of them.[23]

    "Immune" system

    Sponges do not have the complex

    grafts from other species but accept them from other members of their own species. In a few marine species, gray cells play the leading role in rejection of foreign material. When invaded, they produce a chemical that stops movement of other cells in the affected area, thus preventing the intruder from using the sponge's internal transport systems. If the intrusion persists, the grey cells concentrate in the area and release toxins that kill all cells in the area. The "immune" system can stay in this activated state for up to three weeks.[23]

    Reproduction

    Asexual

    The freshwater sponge Spongilla lacustris

    Sponges have three

    archeocytes to produce all the other cell types.[35] A very few species reproduce by budding.[46]

    Gemmules are "survival pods" which a few marine sponges and many freshwater species produce by the thousands when dying and which some, mainly freshwater species, regularly produce in autumn.

    archeocytes that are full of nutrients.[47] Freshwater gemmules may also include photosynthesizing symbionts.[48] The gemmules then become dormant, and in this state can survive cold, drying out, lack of oxygen and extreme variations in salinity.[21] Freshwater gemmules often do not revive until the temperature drops, stays cold for a few months and then reaches a near-"normal" level.[48] When a gemmule germinates, the archeocytes round the outside of the cluster transform into pinacocytes, a membrane over a pore in the shell bursts, the cluster of cells slowly emerges, and most of the remaining archeocytes transform into other cell types needed to make a functioning sponge. Gemmules from the same species but different individuals can join forces to form one sponge.[49] Some gemmules are retained within the parent sponge, and in spring it can be difficult to tell whether an old sponge has revived or been "recolonized" by its own gemmules.[48]

    Sexual

    Most sponges are

    ameboid form and carry the sperm through the mesohyl to eggs, which in most cases engulf the carrier and its cargo.[50]

    A few species release fertilized eggs into the water, but most retain the eggs until they hatch. There are four types of larvae, but all are balls of cells with an outer layer of cells whose

    cilia enable the larvae to move. After swimming for a few days the larvae sink and crawl until they find a place to settle. Most of the cells transform into archeocytes and then into the types appropriate for their locations in a miniature adult sponge.[50]

    syncitium draped around and between them and choanosyncytia with multiple collar bodies in the center. The larvae then leave their parents' bodies.[51]

    Meiosis

    The cytological progression of porifera oogenesis and spermatogenesis (gametogenesis) is very similar to that of other metazoa.[52] Most of the genes from the classic set of meiotic genes, including genes for DNA recombination and double-strand break repair, that are conserved in eukaryotes are expressed in the sponges (e.g. Geodia hentscheli and Geodia phlegraei).[52] Since porifera are considered to be the earliest divergent animals, these findings indicate that the basic toolkit of meiosis including capabilities for recombination and DNA repair were present early in eukaryote evolution.[52]

    Life cycle

    Sponges in

    temperate regions live for at most a few years, but some tropical species and perhaps some deep-ocean ones may live for 200 years or more. Some calcified demosponges grow by only 0.2 mm (0.0079 in) per year and, if that rate is constant, specimens 1 m (3.3 ft) wide must be about 5,000 years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old.[21]

    Coordination of activities

    Adult sponges lack

    Myocytes are thought to be responsible for closing the osculum and for transmitting signals between different parts of the body.[23]

    Sponges contain genes very similar to those that contain the "recipe" for the post-synaptic density, an important signal-receiving structure in the neurons of all other animals. However, in sponges these genes are only activated in "flask cells" that appear only in larvae and may provide some sensory capability while the larvae are swimming. This raises questions about whether flask cells represent the predecessors of true neurons or are evidence that sponges' ancestors had true neurons but lost them as they adapted to a sessile lifestyle.[54]

    Ecology

    Habitats

    glass sponge; seen here at a depth of 2,572 metres (8,438 ft) off the coast of California

    Sponges are worldwide in their distribution, living in a wide range of ocean habitats, from the polar regions to the tropics.[35] Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe.[36] The greatest numbers of sponges are usually found on firm surfaces such as rocks, but some sponges can attach themselves to soft sediment by means of a root-like base.[55]

    Sponges are more abundant but less diverse in temperate waters than in tropical waters, possibly because organisms that prey on sponges are more abundant in tropical waters.

    calcareous sponges are abundant and diverse in shallower non-polar waters.[57]

    The different classes of sponge live in different ranges of habitat:

    Class Water type[23] Depth[23] Type of surface[23]
    Calcarea
    Marine less than 100 m (330 ft) Hard
    Glass sponges
    Marine Deep Soft or firm sediment
    Demosponges Marine, brackish; and about 150 freshwater species[21] Inter-tidal to abyssal;[23] a carnivorous demosponge has been found at 8,840 m (5.49 mi)[42] Any

    As primary producers

    Sponges with photosynthesizing endosymbionts produce up to three times more oxygen than they consume, as well as more organic matter than they consume. Such contributions to their habitats' resources are significant along Australia's Great Barrier Reef but relatively minor in the Caribbean.[35]

    Defenses

    Mercenaria mercenaria, from North Carolina
    Close-up of the sponge boring Entobia in a modern oyster valve. Note the chambers which are connected by short tunnels.

    Many sponges shed

    sea squirts from growing on or near them, making sponges very effective competitors for living space. One of many examples includes ageliferin
    .

    A few species, the Caribbean fire sponge Tedania ignis, cause a severe rash in humans who handle them.[21] Turtles and some fish feed mainly on sponges. It is often said that sponges produce chemical defenses against such predators.[21] However, experiments have been unable to establish a relationship between the toxicity of chemicals produced by sponges and how they taste to fish, which would diminish the usefulness of chemical defenses as deterrents. Predation by fish may even help to spread sponges by detaching fragments.[23] However, some studies have shown fish showing a preference for non chemically defended sponges,[58] and another study found that high levels of coral predation did predict the presence of chemically defended species.[59]

    Glass sponges produce no toxic chemicals, and live in very deep water where predators are rare.[36]

    Predation

    Spongeflies, also known as spongillaflies (Neuroptera, Sisyridae), are specialist predators of freshwater sponges. The female lays her eggs on vegetation overhanging water. The larvae hatch and drop into the water where they seek out sponges to feed on. They use their elongated mouthparts to pierce the sponge and suck the fluids within. The larvae of some species cling to the surface of the sponge while others take refuge in the sponge's internal cavities. The fully grown larvae leave the water and spin a cocoon in which to pupate.[60]

    Bioerosion

    The Caribbean chicken-liver sponge

    mollusks.[21] Sponges may remove up to 1 m (3.3 ft) per year from reefs, creating visible notches just below low-tide level.[35]

    Diseases

    Caribbean sponges of the genus

    cyanobacterium, but it is unknown whether this organism actually causes the disease.[61][62]

    Collaboration with other organisms

    In addition to hosting photosynthesizing endosymbionts,[21] sponges are noted for their wide range of collaborations with other organisms. The relatively large encrusting sponge Lissodendoryx colombiensis is most common on rocky surfaces, but has extended its range into seagrass meadows by letting itself be surrounded or overgrown by seagrass sponges, which are distasteful to the local starfish and therefore protect Lissodendoryx against them; in return, the seagrass sponges get higher positions away from the sea-floor sediment.[63]

    loggerhead sponge, feeding off the larger particles that collect on the sponge as it filters the ocean to feed itself.[65] Other crustaceans such as hermit crabs commonly have a specific species of sponge, Pseudospongosorites, grow on them as both the sponge and crab occupy gastropod shells until the crab and sponge outgrow the shell, eventually resulting in the crab using the sponge's body as protection instead of the shell until the crab finds a suitable replacement shell.[66]

    Bathymetrical range of some sponge species.[67] Demosponge Samus anonymus (up to 50 m), hexactinellid Scleroplegma lanterna (~100–600 m), hexactinellid Aulocalyx irregularis (~550–915 m), lithistid demosponge Neoaulaxinia persicum (~500–1700 m)
    Generalised food web for sponge reefs[68]

    Sponge loop

    Most sponges are

    coral reef food webs by recycling detritus to higher trophic levels.[69]

    The hypothesis has been made that coral reef sponges facilitate the transfer of coral-derived organic matter to their associated detritivores via the production of sponge detritus, as shown in the diagram. Several sponge species are able to convert coral-derived DOM into sponge detritus,[70][71] and transfer organic matter produced by corals further up the reef food web. Corals release organic matter as both dissolved and particulate mucus,[72][73][74][75] as well as cellular material such as expelled Symbiodinium.[76][77][69]

    Organic matter could be transferred from corals to sponges by all these pathways, but DOM likely makes up the largest fraction, as the majority (56 to 80%) of coral mucus dissolves in the water column,[73] and coral loss of fixed carbon due to expulsion of Symbiodinium is typically negligible (0.01%)[76] compared with mucus release (up to ~40%).[78][79] Coral-derived organic matter could also be indirectly transferred to sponges via bacteria, which can also consume coral mucus.[80][81][82][69]

    dissolved organic matter (DOM), (2) sponges take up DOM, (3) sponges release detrital particulate organic matter (POM), (4) sponge detritus (POM) is taken up by sponge-associated and free-living detritivores.[69][83][84]
    , DIN: dissolved inorganic nitrogen)

    Sponge holobiont

    Besides a one to one

    symbiotic relationship, it is possible for a host to become symbiotic with a microbial consortium. Sponges are able to host a wide range of microbial communities that can also be very specific. The microbial communities that form a symbiotic relationship with the sponge can amount to as much as 35% of the biomass of its host.[86] The term for this specific symbiotic relationship, where a microbial consortia pairs with a host is called a holobiotic relationship. The sponge as well as the microbial community associated with it will produce a large range of secondary metabolites that help protect it against predators through mechanisms such as chemical defense.[87]

    Some of these relationships include endosymbionts within bacteriocyte cells, and cyanobacteria or microalgae found below the pinacoderm cell layer where they are able to receive the highest amount of light, used for phototrophy. They can host over 50 different microbial phyla and candidate phyla, including Alphaprotoebacteria,

    Systematics and evolutionary history

    Taxonomy

    Animalia.[89] They have been regarded as a paraphyletic phylum, from which the higher animals have evolved.[90] Other research indicates Porifera is monophyletic.[91]

    The phylum Porifera is further divided into classes mainly according to the composition of their skeletons:[20][35]

    In the 1970s, sponges with massive calcium carbonate skeletons were assigned to a separate class,

    Sclerospongiae, otherwise known as "coralline sponges".[92]
    However, in the 1980s it was found that these were all members of either the Calcarea or the Demospongiae.[93]

    So far scientific publications have identified about 9,000 poriferan species,[35] of which: about 400 are glass sponges; about 500 are calcareous species; and the rest are demosponges.[21] However, some types of habitat, vertical rock and cave walls and galleries in rock and coral boulders, have been investigated very little, even in shallow seas.[35]

    Classes

    Sponges were traditionally distributed in three classes: calcareous sponges (Calcarea), glass sponges (Hexactinellida) and demosponges (Demospongiae). However, studies have shown that the

    Demospongiae, is actually phylogenetically well separated.[94] Therefore, they have recently been recognized as the fourth class of sponges.[95][96]

    Sponges are divided into classes mainly according to the composition of their skeletons:[23] These are arranged in evolutionary order as shown below in ascending order of their evolution from top to bottom:

    Class Type of cells[23] Spicules[23] Spongin fibers[23] Massive exoskeleton[35] Body form[23]
    Hexactinellida
    Mostly
    syncytia
    in all species
    Silica

    May be individual or fused
    Never Never Leuconoid
    Demospongiae
    Single nucleus, single external membrane Silica In many species In some species.
    Made of aragonite if present.[20][35]
    Leuconoid
    Calcarea
    Single nucleus, single external membrane Calcite
    May be individual or large masses
    Never Common.
    Made of calcite if present.
    Asconoid, syconoid, leuconoid or solenoid[97]
    Homoscleromorpha
    Single nucleus, single external membrane Silica In many species Never Sylleibid or leuconoid

    Fossil record

    Raphidonema faringdonense, a fossil sponge from the Cretaceous of England
    1
    2
    3
    4
    5
    6
    7
    1: Gap  2: Central cavity  3 Internal wall  4: Pore (all walls have pores)  5 Septum  6 Outer wall  7 Holdfast
    Archaeocyathid
    structure

    Although

    Chengjiang fauna, from 525 to 520 million years ago.[102] Fossils found in the Canadian Northwest Territories dating to 890 million years ago may be sponges; if this finding is confirmed, it suggests the first animals appeared before the Neoproterozoic oxygenation event.[103]

    Oxygen content of the atmosphere over the last billion years. If confirmed, the discovery of fossilized sponges dating to 890 million years ago would predate the Neoproterozoic Oxygenation Event.

    Freshwater sponges appear to be much younger, as the earliest known fossils date from the Mid-

    demosponges, fossilized remains of this type are less common than those of other types because their skeletons are composed of relatively soft spongin that does not fossilize well.[104]
    The earliest sponge symbionts are known from the

    A chemical tracer is 24-isopropylcholestane, which is a stable derivative of 24-isopropylcholesterol, which is said to be produced by demosponges but not by eumetazoans ("true animals", i.e. cnidarians and bilaterians). Since choanoflagellates are thought to be animals' closest single-celled relatives, a team of scientists examined the biochemistry and genes of one choanoflagellate species. They concluded that this species could not produce 24-isopropylcholesterol but that investigation of a wider range of choanoflagellates would be necessary in order to prove that the fossil 24-isopropylcholestane could only have been produced by demosponges.[106] Although a previous publication reported traces of the chemical 24-isopropylcholestane in ancient rocks dating to 1,800 million years ago,[107] recent research using a much more accurately dated rock series has revealed that these biomarkers only appear before the end of the Marinoan glaciation approximately 635 million years ago,[108] and that "Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, ~713 million years ago in Oman)". While it has been argued that this 'sponge biomarker' could have originated from marine algae, recent research suggests that the algae's ability to produce this biomarker evolved only in the Carboniferous; as such, the biomarker remains strongly supportive of the presence of demosponges in the Cryogenian.[109][110][111]

    Archaeocyathids, which some classify as a type of coralline sponge, are very common fossils in rocks from the Early Cambrian about 530 to 520 million years ago, but apparently died out by the end of the Cambrian 490 million years ago.[102]
    It has been suggested that they were produced by: sponges; cnidarians; algae; foraminiferans; a completely separate phylum of animals, Archaeocyatha; or even a completely separate kingdom of life, labeled Archaeata or Inferibionta. Since the 1990s archaeocyathids have been regarded as a distinctive group of sponges.[89]

    = skin
    = flesh
    Halkieriid sclerite structure[112]

    It is difficult to fit

    bilaterian animals that looked like slugs in chain mail and whose fossils are found in rocks from the very Early Cambrian to the Mid Cambrian. If this is correct, it would create a dilemma, as it is extremely unlikely that totally unrelated organisms could have developed such similar sclerites independently, but the huge difference in the structures of their bodies makes it hard to see how they could be closely related.[112]

    Relationships to other animal groups

    A choanoflagellate
    Simplified family tree showing
    calcareous sponges as closest to more complex animals[115]
     
    Opisthokonta
     

    Fungi

    Choanoflagellates

     
    Metazoa
     

    Glass sponges

    Demosponges

    Calcareous sponges

     Eumetazoa 

    Comb jellies

    Placozoa

    Cnidaria
    (jellyfish, etc.)

    other

    metazoans

    Simplified family tree showing
    Homoscleromorpha as closest to more complex animals[116]
     
    Eukaryotes
     

    Plants

    Fungi

     
    Metazoa
     

    Most demosponges

    Calcareous sponges

    Homoscleromorpha

     Eumetazoa 

    Cnidaria
    (jellyfish, etc.)

    other

    metazoans

    In the 1990s, sponges were widely regarded as a

    choanocytes – which would imply that most Metazoa evolved from very sponge-like ancestors and therefore that sponges may not be monophyletic, as the same sponge-like ancestors may have given rise both to modern sponges and to non-sponge members of Metazoa.[115]

    Analyses since 2001 have concluded that

    calcareous sponges (those with calcium carbonate spicules) than to other types of sponge.[115] In 2007, one analysis based on comparisons of RNA and another based mainly on comparison of spicules concluded that demosponges and glass sponges are more closely related to each other than either is to the calcareous sponges, which in turn are more closely related to Eumetazoa.[100][117]

    Other anatomical and biochemical evidence links the Eumetazoa with

    Homoscleromorpha, a sub-group of demosponges. A comparison in 2007 of nuclear DNA, excluding glass sponges and comb jellies
    , concluded that:

    The sperm of Homoscleromorpha share features with the sperm of Eumetazoa, that sperm of other sponges lack. In both Homoscleromorpha and Eumetazoa layers of cells are bound together by attachment to a carpet-like basal membrane composed mainly of "typ IV" collagen, a form of collagen not found in other sponges – although the spongin fibers that reinforce the mesohyl of all demosponges is similar to "type IV" collagen.[25]

    A comb jelly

    The analyses described above concluded that sponges are closest to the ancestors of all Metazoa, of all multi-celled animals including both sponges and more complex groups. However, another comparison in 2008 of 150 genes in each of 21 genera, ranging from fungi to humans but including only two species of sponge, suggested that comb jellies (ctenophora) are the most basal lineage of the Metazoa included in the sample.[118][119][120][121] If this is correct, either modern comb jellies developed their complex structures independently of other Metazoa, or sponges' ancestors were more complex and all known sponges are drastically simplified forms. The study recommended further analyses using a wider range of sponges and other simple Metazoa such as Placozoa.[118]

    However, reanalysis of the data showed that the computer algorithms used for analysis were misled by the presence of specific ctenophore genes that were markedly different from those of other species, leaving sponges as either the sister group to all other animals, or an ancestral paraphyletic grade.

    cnidarians form the sister group to the bilaterians.[124][125]

    A very large and internally consistent alignment of 1,719 proteins at the metazoan scale, published in 2017, showed that (i) sponges – represented by Homoscleromorpha, Calcarea, Hexactinellida, and Demospongiae – are monophyletic, (ii) sponges are sister-group to all other multicellular animals, (iii) ctenophores emerge as the second-earliest branching animal lineage, and (iv) 

    placozoans emerge as the third animal lineage, followed by cnidarians sister-group to bilaterians.[4]

    In March 2021, scientists from Dublin found additional evidence that sponges are the sister group to all other animals,[126] while in May 2023, Schultz et al. found patterns of irreversible change in genome synteny that provide strong evidence that ctenophores are the sister group to all other animals instead.[127]

    Notable spongiologists

    Use

    Spice Bazaar at Istanbul
    , Turkey)

    By dolphins

    A report in 1997 described use of sponges

    sea bottom.[128] The behavior, known as sponging, has only been observed in this bay and is almost exclusively shown by females. A study in 2005 concluded that mothers teach the behavior to their daughters and that all the sponge users are closely related, suggesting that it is a fairly recent innovation.[17]

    By humans

    Display of natural sponges for sale on Kalymnos in Greece

    Skeleton

    The

    contraceptives. However, by the mid-20th century, overfishing brought both the animals and the industry close to extinction.[130]

    Many objects with sponge-like textures are now made of substances not derived from poriferans. Synthetic sponges include personal and household

    cleaning tools, breast implants,[131] and contraceptive sponges.[132] Typical materials used are cellulose foam, polyurethane foam, and less frequently, silicone
    foam.

    The luffa "sponge", also spelled loofah, which is commonly sold for use in the kitchen or the shower, is not derived from an animal but mainly from the fibrous "skeleton" of the sponge gourd (Luffa aegyptiaca, Cucurbitaceae).[133]

    Antibiotic compounds

    Sponges have

    tumors and fungi.[134][135]

    Other biologically active compounds

    Halichondria produces the eribulin precursor halichondrin B

    Lacking any protective shell or means of escape, sponges have evolved to synthesize a variety of unusual compounds. One such class is the oxidized fatty acid derivatives called oxylipins. Members of this family have been found to have anti-cancer, anti-bacterial and anti-fungal properties. One example isolated from the Okinawan plakortis sponges, plakoridine A, has shown potential as a cytotoxin to murine lymphoma cells.[136][137]

    See also

    References

    1. .
    2. ^ .
    3. .
    4. ^ .
    5. .
    6. .
    7. ^ .
    8. ^ "Henry George Liddell, Robert Scott, A Greek-English Lexicon, Σ ς, , σπλαχρός: , σπόγγος". www.perseus.tufts.edu.
    9. ^ a b Hooper, John (2018). "Structure of Sponges". Queensland Museum. Archived from the original on 26 September 2019. Retrieved 27 September 2019.
    10. PMID 25276334
      .
    11. ^ Vacelet & Duport 2004, pp. 179–190.
    12. ^ Bergquist 1978, pp. 183–185.
    13. ^ Bergquist 1978, pp. 120–127.
    14. ^ Bergquist 1978, p. 179.
    15. .
    16. .
    17. ^ .
    18. ^ Bergquist 1978, p. 29.
    19. ^ Bergquist 1978, p. 39.
    20. ^ .
    21. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae Ruppert, Fox & Barnes 2004, pp. 76–97
    22. PMID 30002868
      .
    23. ^ .
    24. ^ .
    25. ^ .
    26. .
    27. .
    28. .
    29. ^ Ruppert, Fox & Barnes 2004, p. 83, Fig. 5-7.
    30. ^
      PMID 21680406
      .
    31. .
    32. ^ Ruppert, Fox & Barnes 2004, p. 83.
    33. .
    34. ^ "Marine Species Identification Portal: Halisarca dujardini". species-identification.org. Archived from the original on 2020-10-17. Retrieved 2019-08-02.
    35. ^ .
    36. ^ a b c Krautter M (1998). "Ecology of siliceous sponges: Application to the environmental interpretation of the Upper Jurassic sponge facies (Oxfordian) from Spain" (PDF). Cuadernos de Geología Ibérica. 24: 223–239. Archived from the original (PDF) on March 19, 2009. Retrieved 2008-10-10.
    37. S2CID 86297053
      .
    38. .
    39. ^ "4 new species of 'killer' sponges discovered off Pacific coast". CBC News. April 19, 2014. Archived from the original on April 19, 2014. Retrieved 2014-09-04.
    40. ^ (PDF) from the original on 2008-09-06. Retrieved 2008-10-31.
    41. .
    42. ^ .
    43. .
    44. .
    45. ^ Ruppert, Fox & Barnes 2004, p. 239.
    46. ^ Ruppert, Fox & Barnes 2004, pp. 90–94.
    47. ^ Ruppert, Fox & Barnes 2004, pp. 87–88.
    48. ^ .
    49. ^ Ruppert, Fox & Barnes 2004, pp. 89–90.
    50. ^ a b Ruppert, Fox & Barnes 2004, p. 77.
    51. PMID 21672727
      .
    52. ^ a b c Koutsouveli V, Cárdenas P, Santodomingo N, Marina A, Morato E, Rapp HT, Riesgo A. The Molecular Machinery of Gametogenesis in Geodia Demosponges (Porifera): Evolutionary Origins of a Conserved Toolkit across Animals. Mol Biol Evol. 2020 Dec 16;37(12):3485-3506. doi: 10.1093/molbev/msaa183. PMID: 32929503; PMCID: PMC7743902
    53. PMID 15579547
      .
    54. .
    55. .
    56. S2CID 1495896. Archived from the original
      (PDF) on 2008-10-06.
    57. ^ Gage & Tyler 1996, pp. 91–93
    58. S2CID 84799900
      .
    59. .
    60. ^ Piper 2007, p. 148.
    61. ^ a b Gochfeld DJ, Easson CG, Slattery M, Thacker RW, Olson JB (2012). Steller D, Lobel L (eds.). "Population Dynamics of a Sponge Disease on Caribbean Reefs". Diving for Science 2012. Proceedings of the American Academy of Underwater Sciences 31st Symposium. Archived from the original on 2015-09-04. Retrieved 2013-11-17.{{cite journal}}: CS1 maint: unfit URL (link)
    62. PMID 16956064
      .
    63. .
    64. .
    65. ^ Murphy 2002, p. 51.
    66. (PDF) from the original on 2018-07-19. Retrieved 2022-01-24.
    67. .
    68. ISSN 2296-7745. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
      .
    69. ^
      doi:10.3354/meps12443. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
      .
    70. ^ Rix L, de Goeij JM, Mueller CE, Struck U and others (2016) "Coral mucus fuels the sponge loop in warm- and coldwater coral reef ecosystems". Sci Rep, 6: 18715.
    71. ^ Rix L, de Goeij JM, van Oevelen D, Struck U, Al-Horani FA, Wild C, Naumann MS (2017) "Differential recycling of coral and algal dissolved organic matter via the sponge loop". Funct Ecol 31: 778−789.
    72. ^ Crossland CJ (1987) In situ release of mucus and DOC-lipid from the corals Acropora variabilis and Stylophora pistillata in different light regimes. Coral Reefs 6: 35−42
    73. ^ a b Wild C, Huettel M, Klueter A, Kremb S, Rasheed M, Jorgensen B (2004) Coral mucus functions as an energy carrier and particle trap in the reef ecosystem. Nature 428: 66−70
    74. ^ Tanaka Y, Miyajima T, Umezawa Y, Hayashibara T, Ogawa H, Koike I (2009) Net release of dissolved organic matter by the scleractinian coral Acropora pulchra. J Exp Mar Biol Ecol 377: 101−106
    75. ^ Naumann M, Haas A, Struck U, Mayr C, El-Zibdah M, Wild C (2010) Organic matter release by dominant hermatypic corals of the Northern Red Sea. Coral Reefs 29: 649−659
    76. ^ a b Hoegh-Guldberg O, McCloskey LR, Muscatine L (1987) Expulsion of zooxanthellae by symbiotic cnidarians from the Red Sea. Coral Reefs 5: 201−204
    77. ^ Baghdasarian G, Muscatine L (2000) "Preferential expulsion of dividing algal cells as a mechanism for regulating algal-cnidarian symbiosis". Biol Bull, 199: 278−286
    78. ^ Crossland CJ, Barnes DJ, Borowitzka MA (1980) "Diurnal lipid and mucus production in the staghorn coral Acropora acuminata". Mar Biol, 60: 81−90.
    79. .
    80. .
    81. .
    82. .
    83. ^ Rix L, de Goeij JM, van Oevelen D, Struck U, Al-Horani FA, Wild C and Naumann MS (2017) "Differential recycling of coral and algal dissolved organic matter via the sponge loop". Funct Ecol, 31: 778−789.
    84. ^ de Goeij JM, van Oevelen D, Vermeij MJA, Osinga R, Middelburg JJ, de Goeij AFPM and Admiraal W (2013) "Surviving in a marine desert: the sponge loop retains resources within coral reefs". Science, 342: 108−110.
    85. doi:10.1186/s40168-018-0428-1. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
      .
    86. .
    87. ^ .
    88. ^ "Spongia Linnaeus, 1759". World Register of Marine Species. Retrieved 2012-07-18.
    89. ^
      JSTOR 1307076
      .
    90. S2CID 34175521. Archived from the original
      (PDF) on May 9, 2009. Retrieved 2012-08-22.
    91. .
    92. ^ Hartman WD, Goreau TF (1970). "Jamaican coralline sponges: Their morphology, ecology and fossil relatives". Symposium of the Zoological Society of London. 25: 205–243. (cited by MGG.rsmas.miami.edu). Archived 2018-08-18 at the Wayback Machine
    93. .
    94. ^ Bergquist 1978, pp. 153–154.
    95. PMID 21179486
      .
    96. .
    97. .
    98. .
    99. ^ Reitner J, Wörheide G (2002). "Non-lithistid fossil Demospongiae – origins of their palaeobiodiversity and highlights in history of preservation". In Hooper JN, Van Soest RW (eds.). Systema Porifera: A Guide to the Classification of Sponges (PDF). New York, NY: Kluwer Academic Plenum. Archived (PDF) from the original on 2008-12-16. Retrieved November 4, 2008.
    100. ^ .
    101. ^ McMenamin MA (2008). "Early Cambrian sponge spicules from the Cerro Clemente and Cerro Rajón, Sonora, México". Geologica Acta. 6 (4): 363–367.
    102. ^
      S2CID 38837724
      .
    103. .
    104. ^ "Demospongia". University of California Museum of Paleontology. Berkeley, CA: U.C. Berkeley. Archived from the original on October 18, 2013. Retrieved 2008-11-27.
    105. . Retrieved 2015-06-18.
    106. .
    107. .
    108. S2CID 4314662. Archived from the original
      (PDF) on 2018-07-24. Retrieved 2019-08-01.
    109. .
    110. .
    111. .
    112. ^ .
    113. .
    114. S2CID 129127213. free text at Janussen D (2002). "(full text without images)". Journal of Paleontology. Archived from the original
      on December 10, 2008. Retrieved 2008-08-04.
    115. ^ .
    116. ^
      S2CID 34175521. Archived from the original
      (PDF) on May 9, 2009. Retrieved 2008-11-04.
    117. .
    118. ^ .
    119. .
    120. .
    121. .
    122. .
    123. ^ Berwald, Juli (2017). Spineless: the science of jellyfish and the art of growing a backbone. Riverhead Books.[page needed]
    124. PMID 19175291
      .
    125. .
    126. .
    127. .
    128. .
    129. ^ Bergquist 1978, p. 88.
    130. .
    131. .
    132. ^ "Sponges". Cervical Barrier Advancement Society. 2004. Archived from the original on January 14, 2009. Retrieved 2006-09-17.
    133. S2CID 27313678
      .
    134. .
    135. .
    136. .
    137. .

    Bibliography

    External links