Aquatic ecology and Biodiversity

7.3.1. protozoan zooplanktons

Unit 7- Biotic communities
Chaetognaths

Chaetognaths are commonly known as arrow worm or glass worms. They are exclusively holoplanktonic, present in all oceans, live at all depths, however, no one species is found in all latitudes and at all depths. Chaetognaths serve as reliable indicator species as they occur characteristically in warm waters. They are voracious predators, some feed on freshly hatched fish larvae nearly as large as themselves.
Nine genera and about 42 species are recognized. Most species belong to the genus Sagitta, Eukrohnia,Pterosagitta, Spadella etc.. The important forms present in Indian Ocean are Sagitta bombayensis, S. setosa, S. enflata, S. robusta. Spadella sp is the only benthic species present in marine waters.
Planktonic polychaetes

Tomopterus sp

Plank tonic polychaetes are annelids , resembles Neries sp, true holoplanktonic and have wide distribution. Families such as tomopteridae, typooloscolcidae, atciopidae are present in marine waters. Tomopterus sp are the most conspicuous forms of polychaetes present in plankton samples.
Planktonic molluscs
The palnktonic molluscs are represented by pteropods which have wing like extensions of the foot. The holoplanktonic pteropods include two groups, Gymnosomata (Clione sp) without shell and Thecosomata (Cavolinia) with shell. The genera creseis and cavolina are important in marine waters. Besides, among the gastropod molluscs few are pelagic such as, Creseis acicula, Cavolinia tridentate, Janthina roseola etc.

Urochordates
Urochordates are notochordates, gelatinous, holoplanktonic tunicates. Among the protochordiates appendicularians and thaliaceans are important groups. Appendicularians are represented by Oikopleura dioica, Fritillaria venusta and the Thaliaceans by Pyrosoma, Dolioletta gogenbauri, Salpa cylindrica; Salpa fusiformis; Salpa maxima; Salpa thompsoni , Salpa tilsicostata, Thalia democratica etc.They are mostly warm water forms, common in equatorial, temperate and cold seas at the surface. They feed on plankton and forms food for fishes.