Sponge | Wikipedia audio article

Sponge | Wikipedia audio article


Sponges, the members of the phylum Porifera
(; meaning “pore bearer”), are a basal Metazoa (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. The branch of zoology that studies sponges
is known as spongiology. Sponges have unspecialized cells that can
transform into other types and that often migrate between the main cell layers and the
mesohyl in the process. Sponges do not have nervous, digestive or
circulatory systems. Instead, most rely on maintaining a constant
water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges were first to branch off the evolutionary
tree from the common ancestor of all animals, making them the sister group of all other
animals.==Etymology==
The term sponge derives from the Ancient Greek word σπόγγος (spóngos).==Overview==Sponges are similar to other animals in that
they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues
and organs. Some of them are radially symmetrical, but
most are asymmetrical. The shapes of their bodies are adapted for
maximal efficiency of water flow through the central cavity, where the water deposits nutrients
and then leaves through a hole called the osculum. Many sponges have internal skeletons of spongin
and/or spicules (skeletal-like fragments) of calcium carbonate or silicon dioxide. All sponges are sessile aquatic animals, meaning
that they attach to an underwater surface and remain fixed in place (i.e., do not travel). 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.Most species
use sexual reproduction, releasing sperm cells into the water to fertilize 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. Sponges are known for regenerating from fragments
that are broken off, although this only works if the fragments include the right types of
cells. A few 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.In most sponges, an internal gelatinous matrix called mesohyl
functions as an endoskeleton, and it is the only skeleton in soft sponges that encrust
such hard surfaces as rocks. More commonly, the mesohyl is stiffened by
mineral spicules, by spongin fibers, or both. Demosponges use spongin; many species have
silica spicules, whereas some species have calcium carbonate exoskeletons. Demosponges constitute about 90% of all known
sponge species, including all freshwater ones, and they have the widest range of habitats. Calcareous sponges, which have calcium carbonate
spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively
shallow marine waters where production of calcium carbonate is easiest. The fragile glass sponges, with “scaffolding”
of silica spicules, are restricted to polar regions and the ocean depths where predators
are rare. Fossils of all of these types have been found
in rocks dated from 580 million years ago. In addition Archaeocyathids, whose fossils
are common in rocks from 530 to 490 million years ago, are now regarded as a type of sponge. 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. Some studies have shown that sponges do not
form a monophyletic group, in other words do not include all and only the descendants
of a common ancestor. Recent phylogenetic analyses suggest that
comb jellies rather than sponges are the sister group to the rest of animals.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.==Distinguishing features==Sponges constitute the phylum Porifera, and
have been defined as sessile metazoans (multicelled immobile animals) that have water intake and
outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella. However, a few carnivorous sponges have lost
these water flow systems and the choanocytes. 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.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.Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike
all other known metazoans, sponges’ bodies consist of a non-living jelly-like mass (mesoglea)
sandwiched between two main layers of cells. 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”). Sponges have no nervous systems, 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.==Basic structure=====Cell types===A sponge’s body is hollow and is held in shape
by the mesohyl, a jelly-like substance made mainly of collagen and reinforced by a dense
network of fibers also made of collagen. The inner surface is covered with choanocytes,
cells with cylindrical or conical collars surrounding one flagellum per choanocyte. The wave-like motion of the whip-like flagella
drives water through the sponge’s body. All sponges have ostia, channels leading to
the interior through the mesohyl, and in most sponges these are controlled by tube-like
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, while
those at the base of the animal are responsible for anchoring it.Other types of cell live
and move within the mesohyl: 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. Archaeocytes (or amoebocytes) are amoeba-like
cells that are 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.===Glass sponges’ syncytia===Glass sponges present a distinctive variation
on this basic plan. Their spicules, which are made of silica,
form a scaffolding-like framework between whose rods the living tissue is suspended
like a cobweb that contains most of the cell types. 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. 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.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.===Water flow and body structures===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.Although the layers of pinacocytes and choanocytes resemble the 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.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. 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. 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. 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.===Skeleton===
In zoology a skeleton is any fairly rigid structure of an animal, irrespective of whether
it has joints and irrespective of whether it is biomineralized. The mesohyl functions as an endoskeleton in
most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such
as rocks. More commonly the mesohyl is stiffened by
mineral spicules, by spongin fibers or both. Spicules, which are present in most but not
all species, may be made of 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,
and may be separate, connected by joints, or fused.Some sponges also secrete exoskeletons
that lie completely outside their organic components. For example, 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.==Vital functions=====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.===Respiration, feeding and excretion===
Sponges do not have distinct circulatory, respiratory, digestive, and excretory systems
– instead the water flow system supports all these functions. They filter food particles out of the water
flowing through them. Particles larger than 50 micrometers cannot
enter the ostia and pinacocytes consume them by phagocytosis (engulfing and internal digestion). Particles from 0.5 μm to 50 μm are trapped
in the ostia, which taper from the outer to inner ends. These particles are consumed by pinacocytes
or by archaeocytes which partially extrude themselves through the walls of the ostia. Bacteria-sized particles, below 0.5 micrometers,
pass through the ostia and are caught and consumed by choanocytes. Since the smallest particles are by far the
most common, choanocytes typically capture 80% of a sponge’s food supply. Archaeocytes transport food packaged in 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, and these
tracks also move inert objects. It used to be claimed that glass sponges could
live on nutrients dissolved in sea water and were very averse to silt. 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. 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.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.===Carnivorous sponges===
A few species that live in waters where the supply of food particles is very poor prey
on crustaceans and other small animals. So far only 137 species have been discovered. Most belong to the family Cladorhizidae, but
a few members of the Guitarridae and Esperiopsidae are also carnivores. In most cases little is known about how they
actually capture prey, although some species are thought to use either sticky threads or
hooked spicules. Most carnivorous sponges live in deep waters,
up to 8,840 m (5.49 mi), and the development of deep-ocean exploration techniques is expected
to lead to the discovery of several more. However, one species has been found in Mediterranean
caves at depths of 17–23 m (56–75 ft), alongside the more usual 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.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.===Endosymbionts===
Freshwater sponges often host green algae as endosymbionts within archaeocytes and other
cells, and benefit from nutrients produced by the algae. Many marine species host other photosynthesizing
organisms, most commonly cyanobacteria but in some cases dinoflagellates. Symbiotic cyanobacteria may form a third of
the total mass of living tissue in some sponges, and some sponges gain 48% to 80% of their
energy supply from these micro-organisms. In 2008 a University of Stuttgart team reported
that spicules made of silica conduct light into the mesohyl, where the photosynthesizing
endosymbionts live. 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.A recently discovered
carnivorous sponge that lives near hydrothermal vents hosts methane-eating bacteria, and digests
some of them.===”Immune” system===
Sponges do not have the complex immune systems of most other animals. However, they reject 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.===Reproduction=======Asexual====Sponges have three asexual methods of reproduction:
after fragmentation; by budding; and by producing gemmules. Fragments of sponges may be detached by currents
or waves. They use the mobility of their pinacocytes
and choanocytes and reshaping of the mesohyl to re-attach themselves to a suitable surface
and then rebuild themselves as small but functional sponges over the course of several days. The same capabilities enable sponges that
have been squeezed through a fine cloth to regenerate. A sponge fragment can only regenerate if it
contains both collencytes to produce mesohyl and archeocytes to produce all the other cell
types. A very few species reproduce by budding.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. Spongocytes make gemmules by wrapping shells
of spongin, often reinforced with spicules, round clusters of archeocytes that are full
of nutrients. Freshwater gemmules may also include phytosynthesizing
symbionts. The gemmules then become dormant, and in this
state can survive cold, drying out, lack of oxygen and extreme variations in salinity. Freshwater gemmules often do not revive until
the temperature drops, stays cold for a few months and then reaches a near-“normal” level. 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. 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.====Sexual====
Most sponges are hermaphrodites (function as both sexes simultaneously), although sponges
have no gonads (reproductive organs). Sperm are produced by choanocytes or entire
choanocyte chambers that sink into the mesohyl and form spermatic cysts while eggs are formed
by transformation of archeocytes, or of choanocytes in some species. Each egg generally acquires a yolk by consuming
“nurse cells”. During spawning, sperm burst out of their
cysts and are expelled via the osculum. If they contact another sponge of the same
species, the water flow carries them to choanocytes that engulf them but, instead of digesting
them, metamorphose to an ameboid form and carry the sperm through the mesohyl to eggs,
which in most cases engulf the carrier and its cargo.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 flagellae or 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.Glass
sponge embryos start by dividing into separate cells, but once 32 cells have formed they
rapidly transform into larvae that externally are ovoid with a band of cilia round the middle
that they use for movement, but internally have the typical glass sponge structure of
spicules with a cobweb-like main syncitium draped around and between them and choanosyncytia
with multiple collar bodies in the center. The larvae then leave their parents’ bodies.====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.===Coordination of activities===
Adult sponges lack neurons or any other kind of nervous tissue. However, most species have the ability to
perform movements that are coordinated all over their bodies, mainly contractions of
the pinacocytes, squeezing the water channels and thus expelling excess sediment and other
substances that may cause blockages. Some species can contract the osculum independently
of the rest of the body. Sponges may also contract in order to reduce
the area that is vulnerable to attack by predators. In cases where two sponges are fused, for
example if there is a large but still unseparated bud, these contraction waves slowly become
coordinated in both of the “Siamese twins”. The coordinating mechanism is unknown, but
may involve chemicals similar to neurotransmitters. However, glass sponges rapidly transmit electrical
impulses through all parts of the syncytium, and use this to halt the motion of their flagella
if the incoming water contains toxins or excessive sediment. Myocytes are thought to be responsible for
closing the osculum and for transmitting signals between different parts of the body.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.==Ecology=====Habitats===Sponges are worldwide in their distribution,
living in a wide range of ocean habitats, from the polar regions to the tropics. 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. 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.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. Glass sponges are the most common in polar
waters and in the depths of temperate and tropical seas, as their very porous construction
enables them to extract food from these resource-poor waters with the minimum of effort. Demosponges and calcareous sponges are abundant
and diverse in shallower non-polar waters.The different classes of sponge live in different
ranges of habitat:===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.===Defenses===Many sponges shed spicules, forming a dense
carpet several meters deep that keeps away echinoderms which would otherwise prey on
the sponges. They also produce toxins that prevent other
sessile organisms such as bryozoans or 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. Turtles and some fish feed mainly on sponges. It is often said that sponges produce chemical
defenses against such predators. 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. However, some studies have shown fish showing
a preference for non chemically defended sponges, and another study found that high levels of
coral predation did predict the presence of chemically defended species.Glass sponges
produce no toxic chemicals, and live in very deep water where predators are rare.===Predation===
Sponge flies, also known as spongilla-flies (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.===Bioerosion===
The Caribbean chicken-liver sponge Chondrilla nucula secretes toxins that kill coral polyps,
allowing the sponges to grow over the coral skeletons. Others, especially in the family Clionaidae,
use corrosive substances secreted by their archeocytes to tunnel into rocks, corals and
the shells of dead mollusks. Sponges may remove up to 1 m (3.3 ft) per
year from reefs, creating visible notches just below low-tide level.===Diseases===
Caribbean sponges of the genus Aplysina suffer from Aplysina red band syndrome. This causes Aplysina to develop one or more
rust-colored bands, sometimes with adjacent bands of necrotic tissue. These lesions may completely encircle branches
of the sponge. The disease appears to be contagious and impacts
approximately 10 percent of A. cauliformis on Bahamian reefs. The rust-colored bands are caused by a cyanobacterium,
but it is unknown whether this organism actually causes the disease.===Collaboration with other organisms===
In addition to hosting photosynthesizing endosymbionts, 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.Shrimps of the
genus Synalpheus form colonies in sponges, and each shrimp species inhabits a different
sponge species, making Synalpheus one of the most diverse crustacean genera. Specifically, Synalpheus regalis utilizes
the sponge not only as a food source, but also as a defense against other shrimp and
predators. As many as 16,000 individuals inhabit a single
loggerhead sponge, feeding off the larger particles that collect on the sponge as it
filters the ocean to feed itself.==Systematics and evolutionary history=====Taxonomy===
Linnaeus, who classified most kinds of sessile animals as belonging to the order Zoophyta
in the class Vermes, mistakenly identified the genus Spongia as plants in the order Algae. For a long time thereafter sponges were assigned
to a separate subkingdom, Parazoa (“beside the animals”), separate from the Eumetazoa
which formed the rest of the kingdom Animalia. They have been regarded as a paraphyletic
phylum, from which the higher animals have evolved. Other research indicates Porifera is monophyletic.The
phylum Porifera is further divided into classes mainly according to the composition of their
skeletons: Hexactinellida (glass sponges) have silicate
spicules, the largest of which have six rays and may be individual or fused. The main components of their bodies are syncytia
in which large numbers of cell share a single external membrane. Calcarea have skeletons made of calcite, a
form of calcium carbonate, which may form separate spicules or large masses. All the cells have a single nucleus and membrane. Most Demospongiae have silicate spicules or
spongin fibers or both within their soft tissues. However, a few also have massive external
skeletons made of aragonite, another form of calcium carbonate. All the cells have a single nucleus and membrane. Archeocyatha are known only as fossils from
the Cambrian period.In the 1970s, sponges with massive calcium carbonate skeletons were
assigned to a separate class, Sclerospongiae, otherwise known as “coralline sponges”. However, in the 1980s it was found that these
were all members of either the Calcarea or the Demospongiae.So far scientific publications
have identified about 9,000 poriferan species, of which: about 400 are glass sponges; about
500 are calcareous species; and the rest are demosponges. 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.===Classes===
Sponges were traditionally distributed in three classes: calcareous sponges (Calcarea),
glass sponges (Hexactinellida) and demosponges (Demospongiae). However, studies have shown that the Homoscleromorpha,
a group thought to belong to the Demospongiae, is actually phylogenetically well separated. Therefore, they have recently been recognized
as the fourth class of sponges.Sponges are divided into classes mainly according to the
composition of their skeletons:===Fossil record===Although molecular clocks and biomarkers suggest
sponges existed well before the Cambrian explosion of life, silica spicules like those of demosponges
are absent from the fossil record until the Cambrian. One unsubstantiated report exists of spicules
in rocks dated around 750 million years ago. Well-preserved fossil sponges from about 580
million years ago in the Ediacaran period have been found in the Doushantuo Formation. These fossils, which include spicules, pinacocytes,
porocytes, archeocytes, sclerocytes and the internal cavity, have been classified as demosponges. Fossils of glass sponges have been found from
around 540 million years ago in rocks in Australia, China and Mongolia. Early Cambrian sponges from Mexico belonging
to the genus Kiwetinokia show evidence of fusion of several smaller spicules to form
a single large spicule. Calcium carbonate spicules of calcareous sponges
have been found in Early Cambrian rocks from about 530 to 523 million years ago in Australia. Other probable demosponges have been found
in the Early Cambrian Chengjiang fauna, from 525 to 520 million years ago. Freshwater sponges appear to be much younger,
as the earliest known fossils date from the Mid-Eocene period about 48 to 40 million years
ago. Although about 90% of modern sponges are 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. Earliest sponge symbionts are known from the
early Silurian.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. Although a previous publication reported traces
of the chemical 24-isopropylcholestane in ancient rocks dating to 1,800 million years
ago, 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, 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.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. 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. It is difficult to fit chancelloriids into
classifications of sponges or more complex animals. An analysis in 1996 concluded that they were
closely related to sponges on the grounds that the detailed structure of chancellorid
sclerites (“armor plates”) is similar to that of fibers of spongin, a collagen protein,
in modern keratose (horny) demosponges such as Darwinella. However, another analysis in 2002 concluded
that chancelloriids are not sponges and may be intermediate between sponges and more complex
animals, among other reasons because their skins were thicker and more tightly connected
than those of sponges. In 2008 a detailed analysis of chancelloriids’
sclerites concluded that they were very similar to those of halkieriids, mobile 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.===Relationships to other animal groups===In the 1990s sponges were widely regarded
as a monophyletic group, all of them having descended from a common ancestor that was
itself a sponge, and as the “sister-group” to all other metazoans (multi-celled animals),
which themselves form a monophyletic group. On the other hand, some 1990s analyses also
revived the idea that animals’ nearest evolutionary relatives are choanoflagellates, single-celled
organisms very similar to sponges’ 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.Analyses since 2001 have concluded that Eumetazoa (more complex than
sponges) are more closely related to particular groups of sponges than to the rest of the
sponges. Such conclusions imply that sponges are not
monophyletic, because the last common ancestor of all sponges would also be a direct ancestor
of the Eumetazoa, which are not sponges. A study in 2001 based on comparisons of ribosome
DNA concluded that the most fundamental division within sponges was between glass sponges and
the rest, and that Eumetazoa are more closely related to calcareous sponges, those with
calcium carbonate spicules, than to other types of sponge. 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 calcareous sponges,
which in turn are more closely related to Eumetazoa.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: Homoscleromorpha are most closely related
to Eumetazoa; calcareous sponges are the next closest; the other demosponges are evolutionary
“aunts” of these groups; and the chancelloriids, bag-like animals whose fossils are found in
Cambrian rocks, may be sponges. The sperm of Homoscleromorpha share with those
of Eumetazoa features that those 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 “type 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. 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. 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. The results of such an analysis, published
in 2009, suggest that a return to the previous view may be warranted. ‘Family trees’ constructed using a combination
of all available data – morphological, developmental and molecular – concluded that the sponges
are in fact a monophyletic group, and with the cnidarians form the sister group to the
bilaterians.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.==Notable spongiologists====
Use=====
By dolphins===A report in 1997 described use of sponges
as a tool by bottlenose dolphins in Shark Bay in Western Australia. A dolphin will attach a marine sponge to its
rostrum, which is presumably then used to protect it when searching for food in the
sandy sea bottom. 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.===By humans=======Skeleton====The calcium carbonate or silica spicules of
most sponge genera make them too rough for most uses, but two genera, Hippospongia and
Spongia, have soft, entirely fibrous skeletons. Early Europeans used soft sponges for many
purposes, including padding for helmets, portable drinking utensils and municipal water filters. Until the invention of synthetic sponges,
they were used as cleaning tools, applicators for paints and ceramic glazes and discreet
contraceptives. However, by the mid-20th century, over-fishing
brought both the animals and the industry close to extinction. See also sponge diving. 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, and contraceptive sponges. 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).====Antibiotic compounds====
Sponges have medicinal potential due to the presence in sponges themselves or their microbial
symbionts of chemicals that may be used to control viruses, bacteria, tumors and fungi.====Other biologically active compounds====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.==See also==Sponge Reef Project

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