As soon as food receptors detect the approach of a suitable algal cell the maxillae are opened. Water with the cell is sucked into the chamber between the maxillae. When the chamber is closed the water is pressed out again. The algal cell is trapped between the bristles of the maxillae. Many Harpacticoida feed on algae or microbes that cover the substrate.
Some species live inside of macroalgae inducing the growth of galls in which their larvae develop.
On tidal flats many harpacticoid copepods graze on diatoms. Take a closer look at the head appendages of a harpacticoid copepod. Predators and Parasites Most predatory copepods can be found in the Calanoida and Cyclopoida. Parasitic copepods like the Siphonostomatoida and the Poecilostomatoida feed on skin particles of their hosts, others suck blood. The body of the adult stages of some species is extremely modified in adaptation to a parasitic life.