Sea-spider (Nymphon gracile)
|Size||Body length: up to 10 mm (2)|
Common and widespread (2).
The sea-spiders, or pycogonids, are an unusual group of marine arthropods, which are completely unrelated to terrestrial spiders, despite superficially resembling them (3). The body is slender, segmented, and divided into two regions, the head and the trunk (2). The head features a number of pairs of appendages, including two pairs of feeding appendages (chelifores) with pincers at the tips, a proboscis with the mouth at the end, and both sexes have a pair of egg-carrying 'legs' (2). The trunk bears four pairs of long, spindly legs, and has a small projection at the rear called the abdomen (2).
Found on the shores of north-west Europe, and common around British coasts (2).
This species can be found on the middle and lower shore underneath stones and seaweeds (2). It is able to swim, and also lives in shallow water (2).
This sea-spider feeds on a variety of animals, such as small marine worms, sea-anemones and whelk egg-capsules (2). Individuals migrate to the sublittoral zone during the winter breeding season.
The sexes are separate, and males and females cling together during fertilisation. The eggs are released from openings at the base of the female's legs, and are fertilised externally (2). The male carries the eggs around on the special egg-carrying appendages. The larvae are similar in appearance to the adults, and undergo a series of moults before reaching the adult stage after five months. The average life-span is thought to be around one year (2).
Not currently threatened.
Specific conservation action has not been targeted at this species.
For more on this species see A student's guide to the seashore, Fish, J. D. & Fish, S. (1996) (Cambridge University Press).
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- Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Proboscis: a tubular protrusion from the anterior of an animal (e.g. the trunk of an elephant).
- Sublittoral: a marine zone between the littoral zone (the shallow zone where light reaches the bed, subject to submersion and exposure by tides) and depths of around 200m.
- National Biodiversity Network Species Dictionary (January 2003):. http://www.nhm.ac.uk/nbn/
- Fish, J. D. & Fish, S. (1996) A student's guide to the seashore. Second Edition. Cambridge University Press, Cambridge.
- Burnie, D (2001) Animal. Dorling Kindersley, London.