Mesofauna – Enchytraeidae
Morphology
Enchytraeidae are also known as ‘pot worms’ and owe their name to first being discovered in flower pots (from the Greek enchytraeon meaning ‘in the pot’). Each body segment bears four bundles of bristles (setae), two located on the ventral side and two occupying lateral or dorsolateral positions. Numbers of setae per bundle vary between 1 and 16. However, two, three or four are most common, although in some species they are totally absent. Setae are resistant structures, made of chitin, that allow the animal to anchor itself to substrate. Like earthworms and leeches, they are hermaphrodites, as they have reproductive organs normally associated with both male and female sexes. They develop a ‘clitellum’, a glandular modification of the epidermis (the sheet of cells that covers the body of all animals) which secretes a cocoon where the eggs are deposited; however, some species can reproduce through parthenogenesis or asexually by fragmentation.
Taxonomy
The Enchytraeidae are a family of Annelida (class Oligochaeta), resembling small white earthworms (1 – 30 mm in length) that include both terrestrial and aquatic species. Enchytraeids are identified when alive, since the taxonomy uses external and internal structures, which can be clearly seen only through the living transparent body. A single sample generally contains about 1 – 15 (rarely more) species. New species are often found; most subtropical and tropical species are still undescribed.
Microhabitat
Enchytraeids are concentrated in the uppermost soil layers (0 – 5 cm), where organic matter accumulates. Most studies regard them as microbial-feeders, frequently grazing on bacteria and fungal mycelia, although they are also saprovores, consuming dead organic matter.
Diversity, abundance and biomass
About 700 valid species of enchytraeids have been described. Although they are distributed globally, they are more abundant in non-wooded habitats. In particular, cold and wet organic-rich environments, such as moorlands, contain high numbers (ranging from 12 000 to 311 000 individuals per m2), and here enchytraeids are the dominant soil fauna (in terms of live biomass). Seasonal climatic fluctuations have a strong influence on their population dynamics, and extreme weather conditions, such as summer droughts and severely cold winters, can lead to high mortality rates. Although some species can migrate to deeper soil layers to avoid these adverse environmental conditions, this seems to be a short-term survival strategy due to a lack of food in these more humified horizons. Feeding and burrowing activities influence soil structure and turnover of soil organic matter, thus making them ‘ecosystem engineers’, like termites, ants and earthworms.
Ref: A Global Atlas of Soil Biodiversity p 50
