explain the distinguishing characteristics of chordates identify the derived character the craniates that sets castle apart from other chordates describe the developmental fate of the notochord in vertebrates

Vertebrates space members of the kingdom Animalia and the phylum Chordata (Figure (PageIndex1)). Recall that pets that possess bilateral symmetry can be split into two groups—protostomes and deuterostomes—based on their patterns of embryonic development. The deuterostomes, who name converts as “second mouth,” consist of two phyla: Chordata and Echinodermata. Echinoderms room invertebrate marine pets that have pentaradial symmetry and a spiny human body covering, a group that contains sea stars, sea urchins, and also sea cucumbers. The most conspicuous and also familiar members of Chordata are vertebrates, but this phylum additionally includes two groups of invertebrate chordates.

You are watching: Lancelets and tunicates are two groups of chordates

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Figure (PageIndex1): every chordates space deuterostomes own a notochord.

Characteristics that Chordata

Animals in the phylum Chordata re-publishing four vital features that show up at part stage during their development: a notochord, a dorsal hole nerve cord, pharyngeal slits, and also a post-anal tail (Figure (PageIndex2)). In some groups, some of these are current only throughout embryonic development.

The chordates are called for the notochord, i beg your pardon is a flexible, rod-shaped structure that is uncovered in the embryonic stage of every chordates and in the adult phase of some chordate species. That is located in between the cradle tube and the nerve cord, and provides skeletal assistance through the size of the body. In part chordates, the notochord acts together the primary axial support of the body throughout the animal’s lifetime. In vertebrates, the notochord is current during embryonic development, in ~ which time the induces the advancement of the neural tube and also serves together a assistance for the emerging embryonic body. The notochord, however, is not discovered in the postnatal stage of vertebrates; in ~ this point, it has actually been replaced by the vertebral tower (that is, the spine).


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Cephalochordata

Members of Cephalochordata own a notochord, dorsal hollow nerve cord, pharyngeal slits, and also a post-anal tail in the adult phase (Figure (PageIndex4)). The notochord extends right into the head, which gives the subphylum that is name. Die out members the this subphylum incorporate Pikaia, which is the oldest known cephalochordate. Pikaia fossils to be recovered indigenous the burgess shales of Canada and dated come the center of the Cambrian age, make them an ext than 500 million year old.

Extant members that Cephalochordata room the lancelets, called for your blade-like shape. Lancelets are just a few centimeters long and are commonly found hidden in sand at the bottom of warmth temperate and tropical seas. Like tunicates, they space suspension feeders.

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Figure (PageIndex4): The lancelet, choose all cephalochordates, has a head. Adult lancelets retain the four vital features the chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and also a post-anal tail. Water indigenous the mouth beginning the pharyngeal slits, i m sorry filter the end food particles. The filtered water climate collects in the atrium and exits with the atriopore.

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Craniata and Vertebrata

A cranium is a bony, cartilaginous, or fibrous structure bordering the brain, jaw, and also facial skeletal (Figure (PageIndex5)). Many bilaterally symmetrical pets have a head; the these, those that have actually a cranium write the clade Craniata. Craniata consists of the hagfishes (Myxini), which have actually a cranium but lack a backbone, and all of the organisms dubbed “vertebrates.”

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Figure (PageIndex5): Craniata, including this fish (Dunkleosteus sp.), are identified by the presence of a cranium, mandible, and also other facial bones. (credit: “Steveoc 86”/Wikimedia Commons)

Vertebrates room members the the clade Vertebrata. Vertebrates screen the four characteristic features of the chordates; however, members that this group likewise share derived qualities that distinguish them indigenous invertebrate chordates. Vertebrata is named for the vertebral column, created of vertebrae, a series of different bones joined with each other as a backbone (Figure (PageIndex6)). In adult vertebrates, the vertebral tower replaces the notochord, i m sorry is only seen in the embryonic stage.