Salp, clearly showing the muscle bands
Close-up of the opaque gut.
Photos Pierre Niehaus
A chain of salps
Photo Peter Southwood
Salps are tunicates, free-swimming relatives of the sea squirts. They are interesting in that they can occur as solitary individuals, or in groups. When in groups they often form long chains, linked whorls, and other configurations. Salps are active swimmers, and require to swim in order to get water flowing through their hollow bodies, allowing them to filter out any nutrients from the water. In order to swim they have bands of muscle around the cylindrical body, something which is clearly visible in the first photo. They contract the muscles rythmically from one end to the other, causing a compression wave, which propels them like a jet. Salps grow very fast, and some, as can be seen, can attain a fair size, although most are smaller.
See the 27 August 2005 News entry for more details of salps and heir habits and lifestyle, and the 17 July 2005 News entry for the interesting traveller found in the salp shown on the third image.
An introduction to the zooplankton of the Benguela current region, MJ Gibbons, 2005 (?)
Pacific coast pelagic invertebrates, D. Wrobel, C. Mills, 1998
Sealife, G. Walled, ed. 1996.