Chordates derive their name from one of their synapomorphies, or derived features indicating their common ancestry. This is the notochord, a semi-flexible rod. Chordate, any member of the phylum Chordata, which includes the vertebrates (subphylum Vertebrata), the most highly evolved animals, as well as two other subphyla—the tunicates (subphylum Tunicata) and cephalochordates (subphylum Cephalochordata). The phylum Chordata contains. A chordate is an animal belonging to the phylum Chordata; chordates possess a notochord, . However, all tunicate larvae have the standard chordate features, including long, tadpole-like tails; they also have rudimentary brains, light sensors Phylum: Chordata; Haeckel,
|Published:||1 October 2017|
|PDF File Size:||13.4 Mb|
|ePub File Size:||24.18 Mb|
CHARACTERISTICS OF CHORDATES
The water current passes into the atrium and exits through the atrial opening. The difference is that the food consists of somewhat larger particles that have been deposited on the bottom chordate characteristicsand, instead of the feeding current being driven by cilia, the pharyngeal musculature pumps water and food particles across the gill slits.
The earliest fishes probably fed on detritus, and a sucking action is retained chordate characteristics their extant representatives lampreys and hagfishes.
With the development of jaws, it became possible chordate characteristics the vertebrates to capture and seize larger food items.
The lower digestive tract of the primitive chordate is a simple tube with a saclike stomach. There are chordate characteristics indications of the specialized areas and of glandlike structures, such as the liver and pancreas, that occur in vertebrates.
Excretion The excretion of wastes and the control of the chemical composition of the internal environment are largely effected by kidneys, although other parts of the body, including the gills, may play an important role.
Tunicates and cephalochordates have a salt content essentially the chordate characteristics as seawater, but vertebrates, even marine species, have body fluids of low salt content, with the exception of hagfishes.
A possible chordate characteristics is that the vertebrates evolved in fresh water, but it seems reasonable that hagfishes branched off while still marine and that the freshwater form evolved later. Respiration A primitive chordate gill is present in tunicates and cephalochordates, where it serves in both respiration and feeding.
The vertebrate gill may retain some role in feeding, although the current is chordate characteristics produced by the action of muscles, not cilia. The gills became reduced in number in various lineages, and they were strengthened by supporting elements, some of which evolved into jaws.
Lungs, already present in fishes, became the main respiratory organs of terrestrial vertebrates.
Characteristics of Phylum Chordata
Circulatory system The circulatory system in chordates has a characteristic pattern. In tunicates and vertebrates the blood chordate characteristics propelled by a distinct heart; in cephalochordates, by contraction of the chordate characteristics vessels.
Unoxygenated blood is driven forward via a vessel called the ventral aorta. It then passes through a series of branchial arteries in the gills, where gas exchange takes place, and the oxygenated blood flows chordate characteristics the body, much of it returning to its origin via a dorsal aorta.
The blood of vertebrates passes through the tissues via tiny vessels called capillaries. In tunicates and cephalochordates, capillaries are absent and the blood passes through spaces in the tissues instead.
Hormones In vertebrates, endocrine glands those of internal secretion produce hormones that regulate many physiological activities.
Characteristics of Phylum Chordata -
In tunicates and cephalochordates, organs have been identified that correspond in anatomical position to the pituitary gland of vertebrates, but which hormones, if any, they secrete is uncertain.
In vertebrates, the thyroid gland produces thyroxine, an iodine-containing hormone that helps regulate metabolism. The thyroid is a modified endostyle, as can be illustrated by larval lampreys in which the thyroid still secretes mucus for use in feeding.
The endostyles of lancelets take up iodine and form thyroxine, but the thyroxine formed may not function as a hormone in the lancelets themselves. Features of chordate characteristics and aggression Tunicates largely rely upon the passive defense afforded by their heavy tunic.
Lancelets move rapidly through the substrate, and their well-developed locomotory apparatus evolved chordate characteristics to provide a means of escaping predators. Chordate characteristics have ceased to feed on detritus brought to them by water currents.
Morphology of the Chordata
They chordate characteristics shifted to consuming larger foodstuffs and to actively locating, pursuing, and subduing what they eat. Evolution and paleontology Many scientists maintain that chordates originated sometime earlier than million years ago; that is, they chordate characteristics the fossil record.
Such early representatives were soft-bodied and therefore left a poor fossil record. The oldest known fossil chordate is Pikaia gracilens, a primitive cephalochordate dated to approximately million years ago.
There is disagreement over whether older animals—such as Yunnanozoon lividum chordate characteristics Haikouella both of which date to million years ago and possess several chordate features —should be considered chordates.