Skip to main content
Select Source:

Heterostraci

Heterostraci (Pteraspida; heterostracans; superclass Agnatha) Oldest known vertebrate order of jawless, heavily armoured fish-like forms, ranging from the Upper Cambrian to the Devonian. The dermal plates of the body lacked true bone cells and no internal skeleton has been preserved, so this presumably was cartilaginous. The anterior part of the body was covered by large dorsal and ventral plates, with smaller plates to the side. There was a single lateral gill opening, eyes at the sides of the head, and the impression of paired nasal sacs on the inner surface of the rostral shield (which protruded in front of the mouth). The rest of the body was covered by scales; the tail was hypocercal (tilted downwards). Heterostracans were usually only a few centimetres long, although some species reached 1.5m. The body in typical forms, such as the Devonian Pteraspis, was rounded, but the group included dorsoventrally flattened, bottom-dwelling forms such as Drepanaspis.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Heterostraci." A Dictionary of Earth Sciences. . Encyclopedia.com. 18 Dec. 2018 <https://www.encyclopedia.com>.

"Heterostraci." A Dictionary of Earth Sciences. . Encyclopedia.com. (December 18, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/heterostraci

"Heterostraci." A Dictionary of Earth Sciences. . Retrieved December 18, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/heterostraci

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Heterostraci

Heterostraci Alternative name for Pteraspida, an order of fossil jawless vertebrates. See PTERASPIDOMORPHA.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Heterostraci." A Dictionary of Zoology. . Encyclopedia.com. 18 Dec. 2018 <https://www.encyclopedia.com>.

"Heterostraci." A Dictionary of Zoology. . Encyclopedia.com. (December 18, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/heterostraci-0

"Heterostraci." A Dictionary of Zoology. . Retrieved December 18, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/heterostraci-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.