Aquatic ecology and Biodiversity

Unit 7- Biotic communities

7.3. Protozoan zooplankton
Dinoflagellates
Heterotrophic relatives to the phototrophic Dinophyceae; naked and thecate forms. Noctiluca miliaris
Zooflagellates
Heterotrophic nanoflagellates protozoans are foraminiferans, radiolarians and tintinnids.
Foraminiferids and Radiolarians

Foraminifera are single celled protozoans with shells. About 4,000 living species of foraminiferids live in the world's oceans. Of these, 40 species are planktonic. Foraminiferans are protozoans, exclusively marine, few species present in plankton in all oceans. The commonest genus among plankton foraminifera is Globigerina. Species like Orbulina, Globorotalia found in Indian ocean.In contrast to foraminifera, radiolarians are benthic; exclusively pelagic found in all oceans. Radiolarians are spherical, amoeboid cells with silica capsule; 50 µm to several mm; also live in cold water and deep-sea. Shells are siliceous except Acantharia sp. which posses skeleton of strontium. Important genera Acanthometron sp.Thalassiocolla sp. etc.
Ciliates

Ciliates are mostly marine organisms commonly called as tintinids. Tintinids have cosmopoliton distribution and restricted to surface waters and sediments. Important genera found in Indian Ocean are Tintinopsis, Favella, Codonellopsis, Rhabdonella, Eutintinnus etc. They form important food for copepods, euphassids, cladocerans, salpids, chaetognaths, fish larvae etc.
Coelenterates
The coelenterate are gelatinous zooplankton commonly called as jelly fishes, predominated in the zooplankton, solitary, measures few mm. to several meters. They are highly carnivores, do not support good fishery. They often cause nuisance to fishermen using nets and swimmers. Coelenterates characterized by primitive structural organization. Medusae of coelenterates are conspicuous elements of macroplankton having bell shaped or saucer shaped body are meroplanktonic and may occur in large numbers in the coastal waters. Importaent hydrozoans such as Obelia, Bougainvillia, Leukartiara sp. Bougainillia sp, Aequorea sp,. Cosmetira sp., Phillidium sp., Obelia sp, Liriope sp, Aegina sp etc. Important siphonophores are Diphyes sp., Lensia sp., Muggieae, Physalia, Porpita, Velella, etc. The scyphozoans include larger jelly fishes such as Aurelia, Cyanea, Pelagia and Rhizostoma present in the pelagic zone.

Ctenophores

The ctenophores are holoplanktonic, largely present in the plankton samples. They are voracious predators among the plankton found distributed in marine waters. Species of Pleurobranchia sp and Beroe sp are some of the common ctenophores present in the Indian seas.