Araneidae; Cyclosa Menge, 1866. Cyclosa sp. I have been unable to find any pictures of spiders exactly like this one, but there are some specimens shown on the internet which have a similarly shaped abdomen. I have some photos of other spiders which were easier to identify as Cyclosa spp. simply because their webs were adorned with trash. The final clue which gave me some confidence in calling this one Cyclosa sp. was this comment, describing spiders of the Cyclosa Genus in South Africa: "This is a small 5-11mm spider with an elongated abdomen ending in one to four tubercles." http://biodiversityexplorer.info/arachni... Of course, I am assuming that the "bumps" at the posterior end of the abdomen on my specimen are indeed "tubercles"
From Wikipedia: Pollicipes pollicipes grows in groups on rocks, as well as on the hulls of shipwrecks and on driftwood. It is a filter feeder, living on particles that it can glean from the water passing over its extended cirri; these possess a complex assortment of setae, enabling P. pollicipes to have a varied diet, including diatoms, detritus, large crustaceans, copepods, shrimp and molluscs. The larvae pass through seven free-swimming stages (six nauplii and one cypris) over the course of at least a month. After this time, they settle into the adult, sessile form. P. pollicipes is harvested for consumption in many parts of its range, mostly for the Spanish market, where it may sell for as much as €90 per kilogram. As a result, the species is thought to be in decline. It is harvested manually, and archaeological evidence suggests that the species has been harvested in this way for over 10,000 years.