Halanych, Kenneth M. Department of Biological Sciences, Auburn University, Auburn, Alabama.
Cannon, Johanna T. Department of Biological Sciences, Auburn University, Auburn, Alabama.
Benito, Jesús Department of Animal Biology I-Zoology of Invertebrates, University Complutense, Madrid, Spain.
Last reviewed:January 2021
- Reproduction and development
- Related Primary Literature
- Additional Reading
A group of sessile hemichordates that is colonial with small individuals, or zooids, typically 3–6 mm (0.12–0.24 in.) in length. The group Pterobranchia is allied with acorn worms, or enteropneust hemichordates, and there is some question as to whether pterobranchs evolved from within acorn worms. Pterobranchs are suspension feeders that typically live in high-flow regions and feed on algal particles and suspended organic matter. Most species occur in deep cold water, but shallow tropical species are known. Possibly allied to the extinct graptolites, there are approximately 24 living species, divided into two genera. Most of these species live in the Southern Hemisphere. Members of the genus Rhabdopleura (6 species) are distinguished by each individual being housed in its own erect coenecium, a nonchitinous tube secreted by the cephalic shield (Fig. 1). Inside the creeping tube, a tissue process (stolon) forms and connects all the zooids of the colony by budding. In contrast, members of the genus Cephalodiscus (18 species) live in a more open tube, with clusters of individuals sharing a common disklike structure at the end of a flexible trunk (Fig. 2). Some colonies can obtain large sizes [40 cm (16 in.)] while maintaining a series of more open tubes. The cluster consists of several asexually budded individuals that can move as a unit or, presumably, undergo fission to continue asexual reproduction. For both genera, the tube structure, or coenecium, can vary in shape from species to species; it also shows variation in relation to environmental conditions. See also: Enteropneusta; Graptolithina; Hemichordata
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 10,000 highly qualified scientists and 46 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information