Marine Biology

Classification of Benthos-Based on size

Benthic organisms include both plants (phytobenthos) and animals (zoobenthos) and no vertebrates are represented as true benthos.

Based on size

Life in the benthic region is also classified based on size viz. macrobenthos, meiobenthos and microbenthos. Macrobenthos are organisms that are larger than one millimeter like oysters, starfish, lobsters, sea urchins, shrimp, crabs and coral.

 Meiobenthos are between one tenth and one millimeter in size. Organisms in this group include ciliates, annelids, kinorhynchs, copepods, etc., Microbenthos are very tiny organisms like bacteria and ciliates. They are smaller than one tenth of a millimeter.

Types of meiobenthos

Meiobenthos are also called as interstitial organisms (mainly fauna) which live in the spaces between the sand grains or particles of the substratum or live on the individual particles. However, meiofauna is the preferred term to refer to the organisms that live interstitially. Meiobenthos and meiofauna are synonymous terms to each other. These organisms include all animals that pass through a 0.5 mm screen but are retained on a 62 µm screen mesh. This term meiofauna is mainly based on size of the benthic organisms and it does not explain about the location of the organisms or their movements within their habitats. In order to indicate their location and to refine the classification of these forms, some other terms have been introduced as, endobenthic, mesobenthic and epibenthic.

Endobenthic organisms are the meiofaunal sized organisms which move within the sediment by displacing particles (i.e as they are the bigger than the interstitial spaces of the sediment(sand) particles). Mesobenthic organisms are the meiofaunal organisms living and moving within the interstitial spaces of the sand grains. Epibenthic organisms are those that living at the sediment-water interface.