Sponges of the New Caledonian lagoon - IRD

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34 Sponges of the New Caledonian Lagoon sperm fertilizes eggs retained in the female until they develop into ciliated larvae, at which stage they are freed from the parent by evacuation through the exhalant canals and oscules. Embryonic development ends when the larvae swim, using their flagellated external cells for locomotion. This mechanism for dispersal is probably severely limited, given that all known larvae are short-lived (from a few hours to a few days), and some are predominantly demersal (crawling) with a very brief swimming phase. Larvae have been observed swimming in a spiral course: they are polarised and rotate along their anteroposterior longitudinal axis. During this phase larvae may first swarm and then scatter with passive dispersal in the prevailing currents. Around the end of the swimming period larvae slow their movements and become completely demersal. They explore the seabed with their forward swimming pole before settling down and attaching to a suitable substratum. This metamorphosis phase is characterised by the transformation of a polarised, ciliated, mobile larva with no aquiferous system, to a fixed sponge with no anteroposterior axis but with a fully operational aquiferous system. This transformation takes only a few hours. The young, settled sponge is only about a millimetre in diameter, and subsequent growth and survival greatly depend on the particular hydrodynamic conditions operating at the time and other biotic factors, such as predatory grazing nudibranchs, or competition from other organisms competing for limited space. There are many known patterns and strategies of larval behaviour, and there are also many species for which no larvae have yet been recorded. Asexual modes of reproduction include internal or external budding and fragmentation. These strategies are ideal mechanisms for dispersal and recruitment in local populations, and in some habitats, such as HaJimeda beds and other soft substrates, they are thought to be predominant modes of reproduction. Thus, like corals, local populations may consist mostly of clones from single individuals.
How con you s identi fy sponge? o ponge identifications, to be accessible to the non-specialist, must be based on observable morphology, probably with recourse to a light microscope. Some morphological characters vary substantially between widely separated populations, or those living in different habitats, indicating no more than ecophenotypic variation within the species. Other features are much more consistent between individuals irrespective of their geographic distribution. unfortunately, we are still not completely sure which of these "variable characters" indicate population variability within a single species and which are consistent in the evolution of species, and thus are more important in sponge taxonomy. This variation and its relevance to species determinations must be assessed by specialists - who appraise a wide range of characters, biochemical, ultrastructural, ecological and reproductive - and incorporated into a classification which can be interpreted in accessible terms. Over recent years many advances have been made in sponge biology, providing new suites of non-morphological characters discovered from genetic, biochemical and ultrastructural studies. Some of these characters have been useful in supporting or refuting current ideas on morphological-based sponge taxonomy, but in other instances it is difficult to find any morphological characters that correspond to these new schemes: ultimately taxonomy must somehow be related to the morphology of the sponge to be of practical value. Consequently, most sponges are not easy to identify, even for experts, and require specialised techniques as well as an intimate knowledge of the morphological characters. Some of these techniques are outlined below, including the preferred methods for collection, documentation, histological preparation, and a brief explanation of many of the features used to identify sponges. Unfortunately there is, as yet, no taxonomic literature that provides a review or summary of all the morphological characters and all the major groups of sponges below the family level of classification, although such a reference work is in preparation. Knowledge of the vast specialist literature is still essential to effective sponge taxonomy. There are, however, three general books that provide useful insights to sponge classification (see Further Heading). 3S How can you identify o sponge?
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
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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: whiCh are always present irrespecti
Page 39 and 40: Soft parts of the sponge (photo J.
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Page 51 and 52: Anchorate isochela (pl,oto P.R. Ber
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
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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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List of general illustrations provi
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115 Mycale (Zygomycale) parishi (BO
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Sponges of the New Caledonian lagoon - IRD

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