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A combination of experimental work and combing through the scientific literature revealed that most of the animal groups that sit between Platynereis and chordates on the evolutionary tree also have a similar, muscle-based structure in the same position.
Cameron said: "Work from my lab has shown that enteropneusts filter feed using a pharynx perforated with gill slits, just like the invertebrate chordates.
Another characteristic of chordates are myomeres, blocks of muscle tissue often arranged in a zig-zag pattern.
As fossils show, representatives of animal phyla still alive today developed then: mollusks, arthropods, worms of all kinds, and chordates.
The major body plans found in most modern animal groups, such as arthropods and chordates, were established by the Cambrian.
They are now convinced the 2in-long Florida lancelet anchovy, which has hardly changed in more than 500million years, is descended from the earliest chordates, the group from which we are all descended.
ENTEROCOELE the body cavity formed from an outpocketing of the archenteron (a primitive digestive cavity), especially typical of echinoderms and chordates [RHD].
Ascidians are marine invertebrate chordates, some of which are classic model organisms for the study of development and evolution (Conklin 1905; Berrill 1932; Satoh 1994; Corbo et al.
It is estimated that 5 to 8 million insect species have not been identified or discovered (Figure 2), while only 5,000 to 10,000 species of Chordates may await discovery and description (UNEP 1995).
Biodiversity of species resides probably more in tropical rain forests and cloud forests than any other habitat, whereas diversity of phyla (echinoderms, chordates, cnidaria, mollusks, ctenophores) is greatest on the coral reef.
But I would have to base that denial not on the essentiality to animals of their membership in the kingdom Animalia, but on the essentiality to chordates of their membership in the phylum Chordata.
The series will devote hour-long programs to eight of the major body plans--sponges, cnidarians (jellyfish and kin), flatworms, mollusks, annelids (earthworms) arthropods (insects, spiders, lobsters), echinoderms (starfish, sea urchins) and chordates (fish, birds, humans).
For their climate reconstruction, Bucher and his colleagues analyzed the composition of the oxygen isotopes in conodonts, the remains of chordates that once lived in the sea.
Before the lab, 58% of the students named only chordates and 44% named only angiosperms.
These are candidates for genes specific to chordates," says Rokhsar.