Česká geologická služba
Virtual museum
Home  > Taxonomy > Animals > Metazoans > Chordates

Chordates

      Chordates (phylum Chordata) are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Chordata consists of three subphyla: Urochordata, represented by tunicates; Cephalochordata, represented by lancelets; and Craniata, which includes Vertebrata. The Hemichordata have been presented as a fourth chordate subphylum, but they are now usually treated as a separate phylum. Urochordate larvae have both a notochord and a nerve cord which are lost in adulthood. Cephalochordates have a notochord and a nerve cord (but no brain or specialist sensory organs) and a very simple circulatory system. Craniates are the only sub-phylum whose members have skulls. In all craniates except for hagfish, the dorsal hollow nerve cord is surrounded with cartilaginous or bony vertebrae and the notochord is generally reduced; hence, hagfish are not regarded as vertebrates. The chordates and three sister phyla, the Hemichordata, the Echinodermata and the Xenoturbellida, make up the deuterostomes, one of the two superphyla that encompass all fairly complex animals. Attempts to work out the evolutionary relationships of the chordates have produced several hypotheses. The current consensus is that chordates are monophyletic, meaning that Chordata contains all and only the descendants of a single common ancestor which is itself a chordate, and that craniates' nearest relatives are cephalochordates. All of the earliest chordate fossils have been found in the Early Cambrian Chengjiang fauna, and include two species that are regarded as fish, which implies that they are vertebrates. Because the fossil record of chordates is poor, only molecular phylogenetics offers a reasonable prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial. It has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce evolutionary "family trees" give results that differ from traditional classes because several of those classes are not monophyletic. As a result vertebrate classification is in a state of flux.

Source: http://en.wikipedia.org/wiki/Chordates


 

p6438
Ovis ammon p6438
p6134b
Palaeoniscus reussi p6134
p6134
Palaeoniscus reussi p6134
p6134a
Palaeoniscus reussi p6134
p6137
Paleoniscus angustus p6137
p6139
Paleoniscus luridus p6139
p6138
Paleoniscus obliquus p6138
p6135
Paleoniscus rohani p6135
p4890
Perca uraschista p4890
p4892
Perca uraschista p4892
p4891
Perca uraschista p4891
p224
Placodermi McCoy, 1848 p224
p6442
Sus scrofa Linnaeus, 1758 p6442
XB770
Teleostei indet. XB770
JS6
Triturus Rafinesque, 1815 JS6

In the Virtual Museum there are total 436 samples

Virtual museum of the Czech Geological Survey, www.geology.cz, (C) Czech Geological Survey, 2011, v.0.99 [13.12.2011]