The present work summarizes the progress attained in the study of sponge larval ecology since the state-of-the-art reviews performed in the 1970s and stresses the major weaknesses in our current understanding. Most available information on this subject comes from laboratory studies, with just occasional field observations or experiments. The data are also strongly biased because they are mostly derived from just one larval type out the eight types known in the phylum Porifera. Descriptive studies on larval histology are relatively abundant, but investigations directed at unravelling the cytological basis of the main larval behaviors are scarce. Most aspects of basic larval metabolism and sensing processes remain largely not investigated. Modelling of larval ecology is virtually lacking, with no serious attempt to investigate how the major features of larval ecology affect the structure and dynamics of sponge populations. In summary, the ecology of the sponge larva needs further research attention if we are to achieve a global understanding of the biology of the phylum Porifera.
The Porifera (sponges) are often regarded as the oldest, extant metazoan phylum, also bearing the ancestral stage for most features occurring in higher animals. The absence of chitin in sponges, except for the wall of peculiar resistance bodies produced by a highly derived fresh-water group, is puzzling, since it points out chitin to be an autapomorphy for a particular sponge family rather than the ancestral condition within the metazoan lineage. By investigating the internal proteinaceous (spongin) skeleton of two demosponges (Aplysina sp. and Verongula gigantea) using a wide array of techniques (Fourier transform infrared (FTIR), Raman, X-ray, Calcofluor White Staining, Immunolabeling, and chitinase test), we show that chitin is a component of the outermost layer (cuticle) of the skeletal fibers of these demosponges. FTIR and Raman spectra, as well as X-ray difractograms consistently revealed that sponge chitin is much closer to the alpha-chitin known from other animals than to beta-chitin. These findings support the view that the occurrence of a chitin-producing system is the ancestral condition in Metazoa, and that the alpha-chitin is the primitive form in animals.
This chapter reviews the major known monospecific and multispecific sponge aggregations in the world's oceans. They are shown to occur from the intertidal to abyssal depths, in tropical, temperate, and high latitudes and sometimes to create
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