Hydrozoans are members of the phylum Cnidaria. The class Hydrozoa contains about 3800 species, but they often receive little notice because of their small size and relative inconspicuousness. Individuals display either a polypoid or medusoid structure, and some species pass through both forms in their life cycle. The polyp stage usually consists of small branched colonies that can be found attached to various hard substrates, including both natural and artificial surfaces. The medusa, or jellyfish, stage is free-swimming and consists of a gelatinous bell with trailing tentacles. Many of the hydrozoans in NEMESIS have been introduced as part of the fouling community on commercial ships, recreational boats and aquaculture imports, but some have also been introduced through ballast water. The impacts of exotic hydrozoans are varied, with many having no reported impacts, but some species can be fouling pests or may alter planktonic food-webs through predation.

Species List

Amphinema sp.1
Bimeria vestita
Blackfordia virginica
Bougainvillia muscus
Cladonema pacificum
Cladonema radiatum
Clava multicornis
Climacocodon ikarii
Cordylophora caspia
Corymorpha sp. A
Craspedacusta sowerbii
Ectopleura crocea
Ectopleura viridis
Eudendrium carneum
Garveia franciscana
Gonionemus vertens
Laomedea calceolifera
Maeotias marginata
Moerisia lyonsi
Pennaria disticha
Turritopsis dohrnii
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