NAS logo - click to go to the NAS home page Coelenterates (Phylum Coelenterata or Cnidaria) include jellyfish, anemones, corals, and hydras. The phylum is characterized by a gelatinous body, tentacles, and stinging cells called nemadocysts. Most species are found in marine waters, but some occur in brackish or even fresh water. Coelenterates may be either sessile or free swimming, depending on the species and/or stage of the life-cycle. Standard methods of introduction include ship fouling or transportation in ballast water of ocean-going vessels. Potential impacts include competition with native species for suitable substrate or food, negative effects on organisms to which they attach, utilizing native species as a food source, and "swarming", where thousands of jellyfish mass in an area and can affect the local fauna. An example of an introduced coelenterate is the Black Sea jellyfish, Maeotias inexspectata. These small purple jellyfish were introduced via ballast water from Russian ships into San Francisco Bay in 1993. They under went a population explosion and infested tributaries of the bay. This outbreak caused considerable public alarm and inspired news headlines like "Jellyfish Jam the Petaluma River".
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Data Queries and Species Lists

Jellyfish Picture Data Queries
Species List of Nonindigenous Coelenterates
(links to species profiles and collection information)

Links to News and Other Information

General Information

Morphology of Cnidaria
Introduction to Cnidaria

Jellyfish and Hydroids (Scyphozoa and Hydrozoa)

Introduction to Scyphozoa
Introduction to the Hydrozoa

Corals (Anthozoa)

Introduction to the Anthozoa
Systematics of the Anthozoa


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [7/23/2024].

Contact us if you are using data from this site for a publication to make sure the data are being used appropriately and for potential co-authorship if warranted.

For general information and questions about the database, contact Wesley Daniel. For problems and technical issues, contact Matthew Neilson.