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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.