Rützler, Klaus Invertebrate Zoology Department, Smithsonian Institution, National Museum of Natural History, Washington, DC.
Hartman, Willard D. Peabody Museum of Natural History, Yale University, New Haven, Connecticut.
Last reviewed:June 2019
Show previous versions
- Biology and morphology
- Fibrous skeletal elements
- Related Primary Literature
- Additional Reading
A class of the phylum Porifera, including sponges with a skeleton of one- to four-rayed siliceous spicules or of spongin fibers, or both. Four taxonomic classes comprise the phylum Porifera—Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha. Demospongiae is the most abundant and diverse of these classes and is distinguished by three subclasses—Heteroscleromorpha, Keratosa, and Verongimorpha. Several genera lack a skeleton, and it is through a study of these seemingly primitive forms that the complicated structure of most adult members of the Demospongiae (demosponges) may be understood. In general, demosponges (Fig. 1) constitute the most populous and widely distributed group of sponges, occurring in the sea from the tidal zone down to abyssal depths [at least to 5500 m (18,000 ft)]. They contain at least 7500 accepted species (>80% of all sponges) in more than 20 well-defined orders. Most demosponge families are marine, but a few have invaded freshwater habitats. The species vary in size from thin encrustations that are several centimeters in diameter to huge cake-shaped forms that may measure 2 m (6.6 ft) in diameter. Other common shapes are tubular, columnar, arborescent (treelike), cuplike, flabellate (fan-shaped), and excavating (living in galleries bored in limestone). The shallow-water species tend to be more plastic in form than the deep-water species, which usually exhibit little intraspecific variation in shape. See also: Calcarea; Hexactinellida; Porifera
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 9000 highly qualified scientists and 43 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