Bdelloid Rotifer Anatomy.

Bdelloid Rotifers: Intro

Philodina

  Philodina.

Philodina is one of the first rotifers to have been described in detail. Here is an early account of its feeding behaviour given by Henry Baker in a letter to the president of the Royal Society in 1745:

"A Couple of Circular Bodies, armed with small Teeth like those of the Balance-wheel of a Watch, appear projecting forwards beyond the Head, and extending sideways somewhat wider than the Diameter thereof. They have very much the Similitude of Wheels, and seem to turn round with a considerable Degree of Velocity, by which means a pretty rapid Current of Water is brought from a great distance to the very Mouth of the Creature, who is thereby supplied with very many little Animalcules and various Particles of Matter that the Waters are furnished with... "

It is also one of the most frequently encountered of rotifers. It is large and transparent with easily observed internal organs, and is not easily put off going about its normal business -- making it ideal for examination at high magnification.

	Two extended Philodina rotifers with active coronas feed in a field traversed by filaments of algae. The yellow body is the loricate alga Trachelomonas, and a nearly developed egg of the rotifer Lecane is seen in the upper left of the picture. Darkfield, 200X.
	A single Philodina from the same pond water sample as the pair above. It is viewed in ventral aspect, and the ciliated oesophagus can be seen tapering from the buccal cavity between the lobes of the corona to the trophi (jaws) and muscular bulb of the mastax (the surrounding muscular body which actuates the jaws). Darkfield, 200X.
	A single Philodina browsing in a field of filamentous algae and flocculent organic matter. Darkfield, 200X.
	Philodina feeding amongst filaments of algae. Darkfield, 300X.
	Philodina feeding amongst filaments of algae. Darkfield, 200X.
	A rotifer graveyard. Philodina which die and sink to the bottom of the pond or specimen jar decay, leaving their jaws (trophi), the only solid part of their bodies, as their sole mortal remains. This picture shows three sets of Philodina trophi in an amorphous organic mass containing numerous algal cells. Darkfield, 1000X.
	Three Philodina gregaria rotifers browse in a field of clumped organic matter. They are native to the Antarctic, and apart from the unusual bright red colouring of their bodies, are representative of bdelloid rotifers as a whole. Their anatomy is described in more detail in the group of micrographs below. Rheinberg, 100X.

  Philodina gregaria.

Philodina gregaria is native to the Antarctic, where during the summer season, it can be found in such large numbers as to colour the bottoms of lakes and pools a rusty red. The well-known ability of rotifers, particularly the bdelloids, to survive long periods in the frozen state is clearly a survival necessity for P. gregaria, and the specimens in these pictures may be many years or even decades in age -- there is no way of telling.

The brightfield pictures were shot using a Leitz x100/1.2NA water immersion achromatic objective (designed for fluorescence work) and the low-power portion of a Watson Holos achromatic/aplanatic condenser at about 0.4NA. Electronic flash was used for all pictures.

Captions read anticlockwise from the upper left.


More notes on rotifer anatomy are in preparation and will be uploaded soon. Until then, here is a link to some excellently concise notes on the anatomy and behaviour of rotifers using Philodina as an example species.
... and another link to a first-hand account of a dried rotifer cyst taking up water and resulting in an active rotifer (looks like a Philodina) resuming normal behaviour.