Rotifer
Keratella quadrata
Keratella quadrata is a common species of rotifer found in freshwater environments globally. It features a rigid shell called a lorica, often equipped with spines to deter predators. Movement and feeding are facilitated by a ciliated corona at the anterior end. This species is an essential component of the zooplankton, acting as a link between primary producers and higher trophic levels.
Details
Identification
Rigid lorica with six anterior spines, usually two posterior spines, and a characteristic hexagonal pattern on the dorsal surface.
Social behavior
Solitary organisms, though they often occur in high population densities within the plankton.
Diet
Feeds on phytoplankton, bacteria, and organic detritus.
Hunting strategy
Filter feeder; uses the ciliated corona to create a water current that directs food particles to the mouth.
Spawning substrate
Eggs are often carried on the body or released into the open water.
Overwintering
Production of resting eggs that survive unfavorable conditions in the sediment.
Ecology
Ecological role
Primary consumer; converts energy from algae into biomass accessible to fish and larger invertebrates.
Natural predators
Larval fish, predatory zooplankton (e.g., Asplanchna), water fleas.
Competitor species
Other rotifers and cladocerans (water fleas).
Ecosystem service
Food source for fish larvae; contributes to the biological self-purification of water bodies.
Threats
Eutrophication (indirectly), pesticides, acidification of water bodies.
Scientific profile
Profile
Distinguishing features
Six anterior spines, with the median ones being the longest and often curved outwards. Two posterior spines of highly variable length (cyclomorphosis). The central row of facets on the dorsal lorica usually consists of three to four hexagonal fields. Distinguished from K. cochlearis by the presence of two posterior spines and the specific pattern of the facets.
Reproduction
Heterogony: Predominantly parthenogenetic reproduction by amictic females; under stress conditions (density, food shortage), mictic females appear, producing haploid eggs (males) or, after fertilization, resting eggs.
Role in food web
Important primary consumer and link between the microbial loop (bacteria/detritus) and higher trophic levels (fish).
Protection & threats
Status not on standard scale
Main threats
No immediate threats known; the species is widespread and often benefits from anthropogenic eutrophication.