Marine sponges : forty-six sponges of northern New Zealand

Abstract

Sponges are invertebrates and form the only phylum, Porifera, in the subkingdom Parazoa. They are the most primitive of multicellular animals, having neither true tissues nor organs, with the cells showing considerable independence from one another. A sponge is composed of a variety of cells supported by a skeletal network. The skeleton can be composed of spicules and/or spongin. The various cell components perform different functions. The outer surface (pinacoderm) is formed of flattened polygonal cells called pinacocytes. The interior surface (choanoderm) is lined with flagellated collar cells (choanocytes); the flagella beat to provide a current through the sponge enabling oxygen and food particles to be drawn into the sponge and wastes to be expelled. Between the pinacoderm and the choanoderm is an area (the mesohyl) formed of gelatinous material. Cells found here are the basic archaeocytes which can form into any other specialised cell. The body form of sponges is very variable, being influenced by available space, current velocity, habitat, and the nature and slope of the substrate. Asconoid sponges have the simplest form - a tubular shape enclosing a central cavity which opens out through a single exhalent opening (osculum) with porocytes connecting directly from the pinacoderm to the choanoderm. Larger sponges require a more efficient filter system: this is achieved by folding which increases the internal surface area. Syconoid sponges are those with the first stages of body wall folding. Leuconoid sponges have the highest degree of folding, with the formation of flagellated chambers and a complex canal system, the filling in of the central cavity and numerous oscules. The majority of sponges fall into this category. Sponges seem to be unselective feeders: their diet reflects the composition of particles available in the water current, the only criteria being particles smaller than the sieve size of the inhalent openings. Reproduction can be by either sexual or asexual means. Some sponge species contain both male and female sex cells, other species can have different sexes on a permanent or temporary basis. In oviparous sponges eggs are extruded through the exhalent opening, or upon dissolution of the dermal membrane. Viviparous types expel tiny adult sponges or larvae. The larvae usually spend a short time as a free swimming form before settling on the substratum. Asexual forms of reproduction are by budding or splitting. In some species asexual bodies (gemmules) are formed. There are approximately 10,000 species of sponges recorded from around the world.