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Bell Pettigrew Museum
of Natural History
Interpretative Panels
Text: Dr Iain Matthews
Design: Steve Smart & Cavan Convery
A University of St Andrews Development Fund Project
School of Biology
http://biology.st-andrews.ac.uk
3:1 Porifera
P hy l u m
Porifera
S u b p hy l u m
Super class
Body Plan:
• Asymmetrical
• Diploblastic (however the two
layers may not correspond to
those of other animal phyla)
• No enclosed body cavity
• No true gut
Class
Sponges are the most inanimate of animals, they
differ from the typical animal form in that they:
1. show no system of symmetry and therefore
have no dorsal or ventral surface and no
anterior or posterior polarity.
2. lack any nervous or muscular cells.
3. are not composed of tissue and organs,
but are constructed of individual cells.
Poriferans can therefore be considered as being animals
organised at the cellular level. In essence the sponge
body is a bag or cylinder closed at one end and open
at the other. The body is supported by an internal
matrix, the mesohyl, which contains a skeletal system
composed of collagen, spicules of calcium carbonate
or silicon dioxide and fibres of spongin.
Water flows through the cylinder wall, often moved
by the beating of the flagella of specialised choanocyte
cells. The water enters the central cavity or spongocoel
and leaves the body through the osculum.
Surrounding each choanocyte flagellum is a collar
of microvilli which filter food from the passing water.
Describing sponges as possessing only cellular level
organisation is not meant to imply a failure to evolve
multicellularity. The sponges are highly adapted to
their life style. In a sponge the environment is moved
relative to the animal rather than the more normal
reverse situation.
Gut
Endoderm
Ectoderm
The amount of food that can be filtered is dependant
upon the surface area of the layer of choanocytes,
and the most obvious way to increase the area, is to
fold it. The simplest species have remained as simple
‘test tube’ like cylinders (the asconoid form). However
many species possess walls folded in complex patterns
so that the choanocytes lie in channels (syconoid
form [ e.g. Leucandra
] ) or pouches (leuconoid
form [ e.g. Halichondria,
] ).
Being entirely sessile, sponges may appear to be easy
targets for predators. However they are protected by
distasteful or poisonous chemicals and have a biomass
made primarily of rubbery collagen and sharp spicules.
Classification
within
Porifera
Class: Calcarea
Class: Demospongiae
Order: Clathrinida
Order: Homosclerophorida
Order: Leucettida
Order: Choristida
Order: Leucosoleniida
Order: Spirophorida
Order: Sycettida
Order: Lithistida
Order: Inozoida
Order: Hadromerida
Order: Sphinctozoida
Order: Axinellida
Order: Agelasida
Order: Halichondrida
Class: Sclerospongiae
Order: Poecilosclerida
Order: Ceratoporellida
Order: Petrosiida
Order: Tabulospongida
Order: Haplosclerida
Order: Verongiida
Class: Hexactinellida
Order: Dictyocertida
Order: Amphidiscosida
Order: Dendroceratida
Order: Hexactinosida
Order: Lychniscosida
Order: Lyssacinosida
See specimen.
Sponges
Sponges may appear to be very vulnerable to
predation. However much of the animal is made up
of sharp particles of calcium or silica called spicules.
Differences in the shape of these spicules help
scientists to classify the Porifera.
Natural bath sponges
were commonly used for
many purposes. However their collection has now
declined as they are replaced by more sustainable
synthetic alternatives.
Venus’ flower basket is a magnificent sponge from
the seas of Japan and the Philippines. The people
of these countries consider it a symbol of marital
fidelity and it is the local custom to give a bride and
bridegroom a section of this sponge to wish them a
long and happy marriage.