Arrow worms are small, marine, planktonic animals of the phylum Chaetognatha that are found in tropical seas. Most of the 50 species belong to the genus Sagitta. Arrow worms have a head with eyes,
an elongated body—roughly the shape of an arrow— with two pairs of lateral fins and a tail fin. They use hook-like spines on their jaws to prey on smaller planktonic animals and larvae. Arrow worms are cross-fertilizing hermaphrodites; sperm from one individual is received by another in a sperm pouch, which later fertilizes the maturing eggs in the ovary.
Arrow worms are thought to be distantly related to the phylum Chordata (which includes the vertebrates), but they lack many important chordate characteristics. Nevertheless, arrow worms do have a coelom (a fluid-filled body cavity), which is a characteristic of chordates and the phylum Protochordata. In arrow worms it forms as an out-pocket of the larval intestine. A similar organ is also found in the phylum Echinodermata and the subphylum Cephalochordata (Amphioxus) of the phylum Chordata. However, most chordates have a coelom that arises in a different way—by splitting tissue to form the cavity.
"Arrow worms." The Gale Encyclopedia of Science. . Encyclopedia.com. (October 19, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/arrow-worms
"Arrow worms." The Gale Encyclopedia of Science. . Retrieved October 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/arrow-worms
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
The Chicago Manual of Style
American Psychological Association
- 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.