Skeletons reveal New Zealand’s rich sponge biodiversity
Science Centres: Aquatic Biodiversity and Biosecurity
NIWA is investigating new uses for New Zealand’s huge diversity of sponges, including their potential use in a range of biotechnological, cosmetic, and nutraceutical applications. Here we describe the various parts that make up the skeletons of different sponges. This information is essential in selecting those sponge species with potential uses.
Sponges are often the first invertebrates you see when diving in coastal New Zealand waters or peering under ledges on the rocky shore. Some grow like trees from rock faces, others sit like pumpkins or emerge as tubes from the sandy bottom between seaweed-clad rocky reefs, while others encrust algal holdfasts and overhangs on the reef itself. Sponges filter-feed by using collared cells with whip-like tails that beat together to draw a current of water into the many channels in their body. The water is then pumped out again – minus food and oxygen.
One of the fascinating things about sponges is the diversity of their shapes and sizes, which are all largely determined by the nature of their internal skeletons. Some of the more bizarre sponges are found in New Zealand’s deep sea; recent seamount discoveries include a small palm-leaf sponge (Abyssocladia brunni), a tiny English bathing-tent sponge (Tentorium sp.), a hairy flying saucer sponge (Trichostemma irregularis), a minute feather sponge (Asbestopluma biserialis), and a tiny blue chalice sponge (Reidispongia caerulea).
The internal skeleton of a sponge provides structural support, which enables the sponge to inflate to prevent damage to itself in turbulent or abrasive conditions, and, in some cases, to deter predation. The skeleton has two parts: a mineral skeleton of silicon dioxide (silica) or calcium carbonate (calcite) crystals known as spicules, and an organic skeleton made of diverse forms of spongin (collagen) fibre. These features largely determine the sponge’s overall shape, size, and texture, and are fundamental to the way we classify sponges.
Eight skeleton combinations from New Zealand sponges are given below. These range from species with skeletons made up predominantly of silica spicules to species whose skeletons are mostly spongin fibre. Within each of the eight major types of skeleton there are many more variations at the species level. It is the detailed study of these skeletal differences, coupled with their colour, surface features, overall shape, and habitat preference that allows us to recognise new sponge species and to estimate the extent of New Zealand’s sponge diversity.
Which sponge is it?
Sponges are not easy to identify reliably in the field because they can often look the same, and their colour, shape, and texture may change in response to environmental conditions. With the exception of a few well known species, it is almost impossible to find a species name for your sponge without thinly slicing it and examining its skeleton under a microscope. However, it is possible to get some idea of the type of sponge you have by dissolving a small bit of the sponge in household bleach. If spicules are present they will dissolve out of the sponge cellular matrix and can be seen under the microscope. To see if a fibre skeleton is present, and how it is arranged, cut a section about 2 mm thick perpendicular to the sponge surface, and soak it in dilute bleach. This will gently dissolve the sponge cellular matrix away from the tough fibre. Examination of the dissolving section under a microscope, good hand lens, or magnifying glass will show the design of the skeleton, the presence of spicule or sand in the fibre, and any tiny collagen filaments that may be present in the sponge matrix. These skeletons can be stored indefinitely in a sterile saline solution or mounted permanently on a glass slide.
Solid silica (spicule) skeleton |
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Sponge in life 
Aciculites pulchra (Dendy, 1924). |
Skeleton  |
Genus name: Aciculites |
Spicule skeleton cemented by spongin fibre |
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Sponge in life 
Raspailia topsenti (Dendy, 1924). |
Skeleton  |
Genus name: Raspailia |
Spongin fibre skeleton with embedded spicules |
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Sponge in life 
Callyspongia ramosa (Gray, 1843). |
Skeleton  |
Genus name: Callyspongia |
Spongin fibre skeleton with embedded sand grains |
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Sponge in life 
Spongia manipulatus (Cook & Bergquist, 2002). |
Skeleton  |
Genus name: Spongia |
Spongin fibre skeleton with embedded sand grains and a sandy coat |
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Sponge in life 
Psammocinia hawere (Cook & Bergquist, 1998). |
Skeleton  |
Genus name: Psammocinia |
Spongin fibre with knobbed collagen filaments dispersed between fibres |
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Sponge in life 
Ircinia sp. (undescribed). |
Skeleton  |
Genus name: Ircinia |