Sponges of the New Caledonian lagoon - IRD

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42 Sponges of the New Caledonian Lagoan Skeletal structure Structurally the sponge may be divided into two maiar skeletal regions: - The outer surface of the sponge lectosome, dermis or cortex) bounded by a single layer of epithelial cells on the external surface. In same groups there may be a specialised skeleton on the surface [the ectosomal skeleton!, composed of bath or either spongin fibres and spicules. -The inner region of the sponge (choanosomel includes all organic partians of the sponge inside the epithelial cells (mesohyl, comparable to the mesenchyme of higher multicellular animals!, including the water current system. Bath spicules and spongin fibres may be present in the chaanosome, although one or bath may be lost in same groups. Traditionally the chaanosamal region near the periphery is called the subeetosome. The patterns in which the organic and inorganic skeletons grow are informative at all levels of sponge taxonomy and generally useful in their identification. A special terminology has been produced to define this range of skeletal structures, with several categories of Reticulate spicule skeleton and perforate ectO$ome (photo P.R. Bergquist) skeletal architecture recognised lalthaugh combinations and intermediate farms of these may also occur!. I Branching and rejoining network Ireticulate!, producing regular triangular meshes [isodictyal rericulatel or quadrangular meshes (myxillid rericulatel 2. Repeatedly branching but not rejoining (dendriricl 3. Diverging, expanding, but not branching [plumosel. 4. Diverging, simply concentric (radial). S. Disorganised criss-crossed spicule [halichondroidj Perforated ostial surface of ectosame, with renieraid (isodicryal) tangential surface spicule skeleran (photo P. R. Bergquist) ThiCk sponge cortex. with spherasters embedded in ectasame (photo J. N. A. Hooper)
44 Sponges of the New Caledonian Lagoon Spongin fibres and filaments In several orders of sponges the mineral skeleton has been last completely, and lar these groups fibre characteristics are importont in their classification. In other groups, where there is both spongin fibres and spicules, the latter may be portiallyor fully contained inside the former, and thus the skeletal architecture is predominontly dictated by the form of the organic skeleton. In some groups (e.g. some Hoplosclerida) there ore no fibres but spicules ore cemented together with granular collagen. Mostly, though, spongin fibres are useful in identification. Spongin fibres vary both in o hierarchy of size and construction. Three size categories of fibres are generolly recognised [primory, secondory, tertiory fibres!. sometimes differentiated by both size, construction, and the moteriol contoined within eoch type of fibre. In addition to these fibres some groups hove collagen filaments (eg Ircinio!. which are long, thin, convoluted, terminally swollen collagenous structures dispersed within the mesahyl. Several other classes of fibre construction are recognised, based an the amount of spongin protein deposited when the fibre was secreted, and whether or not this spongin was deposited evenly Ihomogeneous fibres) or periodically Istrotilied fibresl Sponges with heavy spongin fibres, often termed 'horny' or 'kerotose' sponges, belong to the orders Dictyocerotido, Dendrocerotido ond Verongido. The most simple fi bres are homogeneous in cross section without o centrol core [or visible pithlle.g. Spongia!. whereas the most'complex' fibres are stratified in cross section, composed of concentric rings of protein I'bork'!, with on optically diffuse pith in the centre of eoch libre le.g. Aplysinal. Intermediate forms are also common, such os Iaund in species of Thorec/a with slightly stratified [laminated) fi bres Inot bark-like!. with 0 granular pith. Mineral skeleton The inorganic or mineral skeleton is traditionally the most important feature for identifying sponges. Th is skeleton moy consist of a fused, coral-like basal skeleton and/or individual components called spicules o Basal skeleton Some groups of sponges secrete 0 secondory, colcareous Ihypercolcified!. spicular bosol skeleton, in addition to free siliceous or calcitic spicules. This feature was once considered diagnostic for a class of sponges known as "sclerosponges", but is now interpreted as a grade of construction lound within both Calcarea ond Demospongiae. The species concerned le.g. As/roscleral usually live in coral reefs and their calcareous skeletons contribute in a minor way to the overall accretion of these reefs. o Spicules These are classified according to five major criteria: 1 Chemical composition These may be silicate or calcitic, indicating division between the classes Demospongioe ond Calcarea. 2. Spicule size - larger spicules, called megosderes, contribute to the skeletal fromework within the sponge, whereas smaller ones, microscleres, are packed between tracts of megoscleres, supporting the soft parts. Spicule sizes are essentiol criterio in defining species, in some examples providing the only easy clues to distinguishing related species, whereas absolute spicule dimensions are less important at higher taxonom ic levels. 3. Spicule fusion - Most spicules ore free within the mesohyl or bound together by the orgonic skeleton, whereas some are characteristically fused together, producing an interlocking or articuloted skeleton. These spicules consist of rigid monospicular skeletons composed of Hypercalcified I)asal ('sclerosponge') skeleton (photo J.N.A. Hooper)
Page 5 and 6: Claude Levi Ed itor Pierre Laboute,
Page 8 and 9: 8 Cel ouurage est le resu/lat d'une
Page 11: This work is the result of a long s
Page 15 and 16: Author profiles Chris Battershill i
Page 17: Clive WiIkinson is Principal Resear
Page 20 and 21: 18 Sponges of the New Caledonian La
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Page 25 and 26: Sponges are fascinating. Each spong
Page 29 and 30: a What IS sponge .- Cll0anocytes in
Page 31 and 32: Sponge structure s ponge adults are
Page 33 and 34: ., Matrix cyanobacleria (photo J. V
Page 35 and 36: whiCh are always present irrespecti
Page 37 and 38: How con you s identi fy sponge? o p
Page 39 and 40: Soft parts of the sponge (photo J.
Page 42: 40 Sponges of the New Coledonian La
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Page 51 and 52: Anchorate isochela (pl,oto P.R. Ber
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Page 57 and 58: The role of sponges In carol reefs
Page 59 and 60: the production of much coral rubble
Page 61 and 62: food material of plant and animal o
Page 63 and 64: The fascinating world of sponge che
Page 65 and 66: It was originally assumed that spec
Page 67 and 68: Sponge diversity, distribution and
Page 69 and 70: predators. Nor do many have adequat
Page 71 and 72: where its life forms were capable o
Page 73: Actual proportions of endemic speci
Page 86: Order Astrophorida 84 I SteJlerro (
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104 Sponges of the New Caledonian L
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Further reading Brien (P.), Levi (C
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Glossary Acantho- Addition of spine
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incorrectly interchanged with the t
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Clathrate Interwoven tubular constr
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Ectosome Peripheral region of the s
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198 Sponges of the New Coledonion L
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202 Sponges of the New Caledonian l
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List of general illustrations provi
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115 Mycale (Zygomycale) parishi (BO
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212 Sponges of the New Caledonion L
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Sponges of the New Caledonian lagoon - IRD

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