Brachionus Labeled – Rotifer Diagram From Corona to Toes

All 14 parts on the diagram

Show the list

Rotifer 14

Corona (wheel organ) The ciliated disc at the front of the head. Its beating cilia look like a turning wheel.
Cilia Fine hairs that fringe the corona. They pull the animal through the water and sweep food to the mouth.
Mouth The opening in the corona that takes in food. A short tube leads back from it to the mastax.
Mastax The round, muscular pharynx behind the mouth. Its jaws grind the food.
Trophi (jaws) The hard jaws inside the mastax. A forked middle piece works against a hammer on each side.
Lorica The stiff, glassy shell around the trunk. It is a thickened part of the cuticle.
Spines Sharp points that the lorica is drawn out into. Six stand along the front edge of this one.
Stomach The large sac where food is digested. Its wall is made of very large cells.
Gastric glands Two glands joined to the front end of the stomach. They make digestive juices.
Intestine The short gut behind the stomach. Waste leaves by an opening on the back, above the foot.
Bladder A small sac that collects waste fluid. It squeezes shut again and again to empty itself.
Eyespot A small spot of pigment on the brain. It senses light.
Foot The slender, ringed tail end of the body. Glands inside it make a sticky cement.
Toes Two small pointed tips at the end of the foot. They steer in swimming and hold on when the animal stops.

How this list was compiled: Every name was checked on 2026-10-03 in at least two of five sources, for facts only and with nothing copied. T. J. Parker and W. A. Haswell, A Text-book of Zoology, volume 1 (1910, public domain), the example of the class, Brachionus rubens, https://archive.org/details/textbookofzoolog00park. H. B. Ward and G. C. Whipple, Fresh-Water Biology (1918, public domain), the chapter on the wheel animalcules, https://archive.org/details/freshwaterbiolog00ward. Wikipedia, Rotifer and Brachionus, https://en.wikipedia.org/wiki/Rotifer. R. W. Hegner, College Zoology (1912, public domain), Rotifera, https://archive.org/details/collegezoology00hegn. FAO Fisheries Technical Paper 361, Manual on the Production and Use of Live Food for Aquaculture (1996), chapter 3, Rotifers, https://www.fao.org/4/w3732e/w3732e0d.htm. Unofficial study material, not affiliated with any textbook, course or exam; check your own course material. Licence: own work

The drawing: Drawn for this site on 2026-10-03 from plain geometry; nothing traced. Licence: own work

How it works

Here is Brachionus labeled: a common pond rotifer seen from above, as a microscope shows it through the clear shell. The names run from the corona at the front to the two toes at the end of the foot.

Read the full guide

The head and the shell

Start at the top. The corona is the disc fringed with cilia, and the mouth sits in the middle of it. The round mastax lies just behind, with the hard trophi inside it. The lorica is the stiff shell around the trunk, with spines on its front edge.

Inside the shell, then the foot

The stomach is the large sac in the middle, with a gastric gland on each side of its front end. The intestine and the bladder lie behind it. The ringed foot leaves the back of the shell and ends in two toes. Press Quiz me to find each part.

Questions and answers

What is the corona of a rotifer?

A disc at the front of the head, fringed with cilia. Their beating pulls the animal through the water and sweeps food to the mouth. The moving cilia look like a turning wheel, which gave rotifers the name wheel animalcules.

What is the lorica of Brachionus?

A stiff, glassy shell around the trunk, made by a thickening of the cuticle. In Brachionus it is thick and hard and often carries spines.

What is the mastax of a rotifer?

A round, muscular pharynx just behind the mouth. It holds hard jaws called trophi, which grind the food before it passes on to the stomach.

Where does Brachionus live?

In fresh water such as ponds and ditches, and some kinds in salty water. It swims freely as part of the plankton.

How many toes does a rotifer have?

Brachionus has two, at the end of the foot. Across the rotifers the foot ends in one to four toes, and in many swimming kinds the foot is small or missing.