HYDROIDS · SVALBARD · PROJECT
Hydroid is the name of the polypoid stage, the asexual generation
in the class Hydrozoa.
Most of the hydrozoan species undergo indirect development, in which benthic,
asexual hydroid stages alternate with free-swimming, sexually reproductive medusae.
In half of the species medusa stage is suppressed. In these cases, the medusa does not
leave the hydroid colony but is maintained at different stages of development on the polyp
as a sporosac (fixed gonophore).
The class Hydrozoa is a monophyletic group of about 3 500 described species in the phylum Cnidaria.
Hydrozoans are mostly marine, but they can also live in brackish and freshwater systems. In the seas
they inhabit all latitudes and all depths. The class comprises two monophyletic subclasses; this
division is supported by molecular phylogenetic analyses. Hydroidolina, the first subclass, includes
three orders (Leptothecata, Anthoathecata and Siphonophorae). There are about 3 220 valid species that
are highly diversified in hydroid and medusa morphologies and in life cycles. Trachylina, the second
subclass, comprises roughly 150 valid species that are classified into four orders: Limnomedusae,
Trachymedusae, Narcomedusae, and Actinulidae. The subclass Trachylina is characterized by the absence
of the polyp stage in most of its species. A very reduced and modified polyp stage can appear only in
the order Limnomedusae.
Classification:
Svalbard is a Norwegian archipelago located between 74o and 81oN and between 10o and 35oE. It comprises
about 150 small islands and a few larger ones (Spitsbergen, Nordaustlandet, Edgeoya, Prins Karls
Forland and Barentsoya). The archipelago is located on the western edge of the Barents Sea shelf. The
west coast of Spitsbergen is under the influence of the relatively warm West Spitsbergen Current that
carries saline, Atlantic water (T>2°C, S>34.7 PSU). The eastern and northern parts of archipelago are
affected by the colder Arctic water (T<0°C, S=34.3-34.8 PSU). About 60% of the Svalbard land mass is
covered by glaciers.
The main aim of the project is to present a hydroids diversity in the Arctic waters of Svalbard Archipelago.
Special effort is undertaken to describe and picture each species in the way that may be helpful to marine
biologist without taxonomical training to identify taxa to the lowest level possible.
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