The Rotifer Jaw

by Mike Morgan, UK. February 1998

The following may be of interest, whilst observing a sample of pond water, I found a good example of the jaws of a rotifer (Brachionus). The mouth of the rotifer leads to the pharynx which contains the jaws or trophi. The jaws consist of seven, hard cuticularized parts, which retain their shape after death or compression, though not necessarily their relative positions.

The basic constituents of the jaw are one fulcrum, and a pair each of unci, rami and manubria. There are several jaw types: malleate, incudate, virgate, uncinate, ramate and malleoramate. The type of jaw observed forms the basis for division into families.

F fulcrum; M manubrium; R ramus; U uncus.

The easiest jaw type to recognize, and shown here, is the malleate type, which is characteristic of the Brachionidae. All parts of the jaw are well developed and strong. The fulcrum is short and the rami broad. The unci have ridges across the surface terminating in teeth at the inner edge. The action of the jaw is to cut and chew, between the teeth, particles collected.

Comments to the author
Mike Morgan welcomed.

Image notes:
Ventral View, in both videoed image and diagram are the jaws of Brachionus calyciflorus.


Life in a Drop of Pond Water (The Rotifera) Mike Morgan

With thanks to Rosalind Pontin for permission to use text and illustration from her book 'A Key to British Freshwater Planktonic Rotifera'.

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