Class: Pycnogonida (sea spiders)
> Kingdom: Metazoa (animals) > Phylum: Arthropoda
> Subphylum: Cheliceriformes
Pycnogonids bear a superficial resemblance to terrestrial
spiders (Araneae) and are found in the sea, hence their common name 'sea
spiders'. They are strange-looking animals because they have long legs in
relation to the body. Over 1000 species in nearly 100 genera have been named
worldwide and evidently there are many more species still to be described.
Sixty-four species are known from the seas round South Africa (Adie et al. 2005).
are found from intertidal regions down to a depth of nearly 7000 metres and our
found in oceans worldwide. They range in size from a leg span of only 2 mm
through to deep sea species in the genus Colossendeis that have leg spans
of up to 60 cm.
The defining characters of the pycnogonids are as follows:
- unique pre-oral proboscis (no proboscis in other
- ovigers, which are specialised leg-like
appendages between the pedipalps and first pair of walking legs (absent in
females of some species). They can be used in a number of ways but in males
are used for brooding batches of eggs that are obtained from the female (see
Life Cycle below).
- opisthosoma reduced or absent (reproductive
systems extend into the legs so the legs help in storing organs that would
normally take up space in the opisthosoma).
- walking legs nine-segmented (up to 7-segmented
in other cheliceriformes [check]).
- multiple pairs of gonopores, located on some or
all legs (1 pair in other cheliceriformes).
Most species are predators of hydroids, nudibranchs,
polychaetes and other small invertebrates. These species feed by using three
cuticular teeth at the end of the proboscis to pierce their prey and they then
suck out the contents of their prey through the proboscis. In addition to the
predators, there are some species that feed on algae and others that scavenge.
- Legs of females are usually swollen in the femur to
provide space for storing unfertilised eggs.
- Legs with eggs have gonopores at their base through
which the eggs are laid.
- The male fertilizes the eggs as they are laid by the
female - he either hangs beneath her or is over her back.
- The male gathers up the eggs and glues them to his
ovigers using a sticky solution from special femoral glands.
- After the eggs have been looked after by the male for
some time, they typically hatch out as unique protonymphon larvae but in
some species they hatch out as juveniles that are miniature versions of the
- The protonymphon larvae live symbiotically with
cnidarians, molluscs or echinoderms. This relationship appears to be
parasitic in some cases and commensal in others.
- The larva passes through a series of moults in which
segments and appendages are added on to produce a juvenile.
- The juvenile becomes free-living (?)
Adie, H., Wethered, R., Herbert, D. &
Lewis, F. 2005. The state of the nature of South African biosystematics
study. Final Report. Institute of Natural Resources, Scottsville,
Pietermaritzburg Investigational Report No. 254.
Arnaud, F & Child, C.A. 1988. The South
African Museum's Meiring Naude cruises. Part 17. Pycnogonida. Annals of
the South African Museum 98: 121-187.
Brusca, R.C. & Brusca, G.J. 2003. Invertebrates
- 2nd Edition. Sinauer Associates, Sunderland, Massachusetts.
Stock, J.H. 1962. Second list of Pycnogonida
of the University of Cape Town ecological survey. Transactions of the
Royal Society of South Africa 36: 273-286.
Stock, J.H. 1963. South African deep-sea
Pycnogonida, with descriptions of five new species. Annals of the South
African Museum 46: 321-340.