A salp is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body. The most abundant concentrations of salps are in the Southern Ocean (near Antarctica), where they sometimes form enormous swarms, often in deep water, and are sometimes even more abundant than krill...You learn something every day.
When food is plentiful, salps can quickly bud off clones, which graze the phytoplankton and can grow at a rate which is probably faster than that of any other multicellular animal, quickly stripping the phytoplankton from the sea. But if the phytoplankton is too dense, the salps can clog and sink to the bottom. During these blooms, beaches can become slimy with mats of salp bodies...
Although salps appear similar to jellyfish because of their simple body form and planktonic behavior, they are chordates: animals with dorsal nerve cords, related to vertebrates, animals with backbones.
Image via Boredom Therapy, where there are more photos.
Fascinating. I wonder how far back the natural history of salps goes. Specifically, are they among the first chordates?
ReplyDeleteIf they are then they'd be among the first to branch off the evolutionary tree while cnidarians went another direction.
Your knowledge of the animal tree and grasp of tree thinking is a bit off. Tunicates (the group including salps) and their sister taxon, Craniates (us), both go back to the Early Cambrian, arising at the same time as each other. Both are more closely related to each other than either is to Cephalochordates (lancelets), which also go back to the Early Cambrian. These make up the Chordata, which are related to the hemichordates (acorn worms) and echinoderms (sea urchins and such). All of these are in Deuterostomia, which is in turn sister to Proterostomia (almost all other animals except a couple small "worm" clades and extinct worm-like groups). These all form the Bilateria, which are sister to Cnidaria. So there's quite a few major splits before you get to jellyfish and their kin. Outside that pairing are the placozoans, ctenophores, and sponges, in turn.
DeleteThere are very few fossil tunicates, but there is an extinct salp from the Mississippian. http://www-personal.umich.edu/~wstoddar/salp.html
Keep in mind, though, that that does not mean living salps are relics of the past, living fossils, or anything of the sort. It's a large group same as tetrapods (including us). There's no such thing as a living fossil. It's a horrible term. The bane of my existence as a paleontologist.
Thank you for the corrections and clarifications. And I will never use the term "living fossil" ever again.
ReplyDeleteHurrah, thanks! ^_^
Delete(although David Attenborough used the term on a recent episode of Blue Planet II...)
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