ADW: Porifera: INFORMATION
Animal Diversity Web
http://animaldiversity.ummz.umich.edu/accounts/Porifera/
University of Michigan Museum
of Zoology
Porifera
sponges
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By Phil Myers
Sponges are a diverse group of sometimes common
types, with about 5000 species known across the world.
Sponges are primarily marine, but around 150 species
live in fresh water. Sponges have cellular-level
organization, meaning that that their cells are
specialized so that different cells perform different
functions, but similar cells are not organized into tissues
and bodies are a sort of loose aggregation of different
kinds of cells. This is the simplest kind of cellular
organization found among parazoans.
Other characteristics of sponges include a system of
pores (also called ostia) and canals, through which water
passes. Water movement is driven by the beating of
flagellae, which are located on specialized cells called
choanocytes (collar cells). Sponges are either radially
symmetrical or asymmetrical. They are supported by a
skeleton made up of the protein collagen and spicules,
which may be calcareous or siliceous, depending on the
group of sponges examined. Skeletal elements,
choanocytes, and other cells are imbedded in a
gelatinous matrix called mesohyl or mesoglea. Sponges
capture food (detritus particles, plankton, bacteria) that
is brought close by water currents created by the
choanocytes. Food items are taken into individual cells
by phagocytosis, and digestion occurs within individual
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Classification
Kingdom
Animalia
animals
Unspecified
Porifera
sponges
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ADW: Porifera: INFORMATION
http://animaldiversity.ummz.umich.edu/accounts/Porifera/
cells.
Reproduction by sponges is by both sexual and asexual
means. Asexual reproduction is by means of external
buds. Some species also form internal buds, called
gemmules, which can survive extremely unfavorable
conditions that cause the rest of the sponge to die. Sexual
reproduction takes place in the mesohyl. Male gametes
are released into the water by a sponge and taken into
the pore systems of its neighbors in the same way as food
items. Spermatozoa are "captured" by collar cells, which
then lose their collars and transform into specialized,
amoeba-like cells that carry the spermatozoa to the eggs.
Some sponges are monoecious; others are dioecious. In
most sponges for which developmental patterns are
known, the fertilized egg develops into a blastula, which
is released into the water (in some species, release takes
place right after fertilization; in others, it is delayed and
some development takes place within the parent). The
larvae may settle directly and transform into adult
sponges, or they may be planktonic for a time. Adult
sponges are generally assumed to be completely sessile,
but a few studies have shown that adult sponges in a
variety of species can crawl slowly (Bond and Harris
1988).
Sponges have three different types of body plans,
although these morphologies do not define taxonomic
groups. Asconoid sponges are shaped like a simple tube
perforated by pores. The open internal part of the tube is
called the spongocoel; it contains the collar cells. There
is a single opening to the outside, the osculum. Syconoid
sponges tend to be larger than asconoids and have a
tubular body with a single osculum. The synconoid body
wall is thicker and the pores that penetrate it are longer,
forming a system of simple canals. These canals are lined
by collar cells, the flagellae of which move water from
the outside, into the spongocoel and out the osculum.
The third category of body organization is leuconoid.
These are the largest and most complex sponges. These
sponges are made up of masses of tissue penetrated by
numerous canals. Canals lead to numerous small
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ADW: Porifera: INFORMATION
http://animaldiversity.ummz.umich.edu/accounts/Porifera/
chambers lined with flagellated cells. Water moves
through the canals, into these chambers, and out via a
central canal and osculum. Sponges in the class Calcarea,
considered to be the most primative group, and have
asconoid, synconoid and leuconoid members. The
Hexactinellida and Demospongiae groups have only
leuconoid forms.
Sponges are found in virtually all aquatic habitats,
although they are most common and diverse in the
marine environment. Many species contain toxic
substances, probably to discourage predators. Certain
other marine animals take advantage of this
characteristic of sponges by placing adult sponges on
their bodies, where the sponges attach and grow. The
chemicals also probably play a role in competition
among sponges and other organisms, as they are released
by sponges to insure themselves space in the marine
ecosystem. Some of these chemicals have been found to
have beneficial pharmaceutical effects for humans,
including compounds with respiratory, cardiovascular,
gastrointestinal, anti-inflammatory, antitumor, and
antibiotic activities. Sponges also provide a home for a
number of small marine plants, which live in and around
their pore systems. Symbiotic relationships with bacteria
and algae have also been reported, in which the sponge
provides its symbiont with support and protection and
the symbiont provides the sponge with food. Some
sponges (boring sponges) excavate the surface of corals
and molluscs, sometimes causing significant degradation
of reefs and death of the mollusc. The corals or molluscs
are not eaten; rather, the sponge is probably seeking
protection for itself by sinking into the hard structures it
erodes. Even this process has some beneficial effects,
however, in that it is an important part of the process by
which calcium is recycled.
Sources:
Brusca, R. C., and G. J. Brusca. Invertebrates. 1990. Sinauer
Associates, Sunderland, MA.
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ADW: Porifera: INFORMATION
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Bond, C. and A. K. Harris. 1988. Locomotion of sponges
and its physical mechanism. Journal of Experimental
Zoology volume 246, pages 271-284.
Hickman, C.P. and L. S. Roberts. 1994. Animal Diversity.
Wm. C. Brown, Dubuque, IA.
Pearse, V., J. Pearse, M. Buchsbaum, and R. Buchsbaum.
1987.
Living
Invertebrates.
Blackwell
Scientific
Publications, Palo Alto, Ca.
Porifera/*
Contributors
Phil Myers (author), Museum of Zoology, University of
Michigan-Ann Arbor.
To cite this page: Myers, P. 2001. "Porifera" (On-line), Animal Diversity Web. Accessed October 02,
2013 at http://animaldiversity.ummz.umich.edu/accounts/Porifera/
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