Rotifer Resting Eggs In contrast to bdelloid (digonont) rotifers the monogonont rotifers produce several types of eggs. The first type (and most common) is the amictic egg. During the individual lifetime the females produce amictic eggs which are diploid and are not fertilized by any males. Out of these eggs amictic females hatch (parthenogenesis). The parthenogenesis is an effective way to colonise and exploit a new habitat. The population starts with few individuals; by parthenogenesis the population grows exponentially, food resources (e.g planctonic algae) can be exploited very fast. When the population density increases the chances to find a sexual partner increases, but food resources get low. If the environmental conditions get bad (low food, unsuitable temperature etc.) the females start producing two types of eggs: mictic eggs which are haploid, but look like the amictic eggs and male eggs (haploid), which are smaller. From the small male eggs the small male rotifers hatch, which lack the digestive tract including the mastax with the trophi. The males mate with the mictic females; their (haploid) sperms fertilize the mictic eggs, which are then diploid. These eggs are called resting eggs. The look different from the amictic eggs. They typically have a very solid shell, often with spines or a layer of bubble-like cells around the yolk in the center. The resting eggs can survive bad environmental conditions. If the environmetal conditions become suitable agiain new amictic females hatch from these resting eggs and the cycle starts again. The life cycle of monogonont rotifers Polyarthra vulgaris: specimen with parthenogenetic diploid amictic egg. The eyespot of the daughter can be recognized in the egg. Polyarthra vulgaris; specimen with male eggs (males hatch out of these eggs only ) which are obviously smaller than the amictic female eggs. Polyarthra vulgaris; the male has no eyespot and is very small. The arrowheads point to some of the sperm cells. Pe: penis; Ft: foot the conspicuous orange spot is a lipid droplet (DIC). Polyarthra dolichoptera carrying a resting egg . some resting eggs Filinia longiseta; resting egg Filinia longiseta; resting egg left image: Ptygura pilula ; resting egg right image: Polyarthra vulgaris Hexarthra mira ; resting egg Euchlanis triquetra ; resting egg Ascomorpha ecaudis ; resting egg Asplanchna girodi; resting egg Lecane bulla; while in many species the resting eggs are carried around by the femalesoutside of the body. In other species the resting eggs remain in the body of the mother until death. The lorica of the corpse may serve as a protection of the egg. If the lorica desintegrates the resting egg is set free.
freshwater life procaryota algae plants protists "worms" molluscs arthropods marine life mediterranean tropical misc impresssum plingfactory