Giant sea spider

Educational value

• Sea spiders, or pycnogonids, are a group of marine animals only distantly related to terrestrial spiders despite their name and appearance. They are found in all seas including those of Australia and New Zealand and even the polar regions. While most inhabit shallow water there are many deep-sea species. Sea spiders are generally small with a leg span of 5-40 mm, although some huge deep-sea species commonly have a leg span of 50 cm or more.
• Most sea spiders feature long well-developed legs and reduced bodies. The legs of sea spiders are unique as they contain many of the essential organs associated with the digestive and reproductive systems, while their bodies are much reduced in size and function. Sea spiders lack a respiratory system, exchanging gases by diffusion through the body surface. Sea spiders have one, two or, rarely, four pairs of eyes. In some deep-sea species, the eyes are absent.
• Sea spiders are mostly carnivorous predators or scavengers, using a proboscis (long feeding tube) containing the mouth to suck nutrients from soft-bodied invertebrates such as hydroids, sponges, worms and sea anemones. They generally walk slowly along the sea floor to locate prey. Long-legged species are able to tread water (swim) and so can be carried along by currents and tides.
• Typically, sea spiders are a uniform orange-red colour in live specimens. It is thought that some take on the colouration of their surroundings, including that of the animals they feed upon, in order to blend in.
• 'Dodecalopoda mawsoni' is a deep-sea species, one of only two known species with 12 legs. 'Dodecalopoda mawsoni' is large, measuring about 50 cm from the tip of one leg to the other. The remarkably long thin legs of many giant species are probably adapted for gentle walking on the soft muddy substrate of the deep sea.
• Although 10-legged and 12-legged species have never been recorded in Australian waters, giant 8-legged species are among the many deep-sea animals collected by Museum Victoria off Australia's south-east coast since the 1980s. This challenging environment has been sampled using dredges, trawls and grabs from ships. A diverse collection of fish, crabs, lobsters, molluscs, corals and sponges have been collected, including many new species.

Year level

F; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12

Topics Invertebrates