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Batillipes - Males and Females

Okay, the marine tardigrades are difficult to spot and difficult to observe. But in one respect things are easier than with their terrestric relatives: Males and females can be told apart without problems. Remember, there are many terrestric species where males are rare, unknown, possibly even not existing.

With Batillipes the male/female individual count appears to be equilibrated and it is fairly easy to recognize males and females already at moderate magnifications under the dissecting microscope.

[ Marine tardigrade ]

Batillipes tardigrade on sand grain.

[ Batillipes female ]

Batillipes tardigrade female on sand grain. Ovary (white) above the stomach which is filled with green algae. Body length ca. 0.2 mm.

At the female's hind body the eggs can be seen in top view as well, sometimes to the left, sometimes to the right, but apparently never on both sides of the intestine. The pathway of the developing eggs can be seen here:

[ Batillipes female ]

Batillipes tardigrade female on sand grain. Ovarium (white) above the stomach which is filled with brow algae. A mature egg can be seen at the very end of the hind body. Body length ca. 0.2 mm.

The eggs (typically one or two) are positioned asymmetrically, always only on one side of the intestine. They look like grey spots in incident light.

[ Batillipes female ]

Batillipes tardigrade female as seen under incident light with the dissecting microscope. The egg appears as a grey roundish shape, hind side, to the right.

Now as we know where to look out for the eggs we are able to spot them in transmitted light as well.

[ Batillipes female]

Batillipes mirus tardigrade female. Transmitted light. The egg appears as a greyish sphere near the anatomically left hind leg, here on the right side.

[ Batillipes female ]

Batillipes tardigrade female. Transmitted light. Same situation, detail of hind body as seen at slightly stronger magnification.

And how about the males? Are they just females lacking eggs?
No. There are characteristic anatomical details. The symmetrical ending of the intestine indicates symmetrical anatomy, according to literature found only in the case of Batillipes males.

[ Batillipes male ]

Batillipes male. Transmitted light.

Though somewhat difficult to photograph you might see the pinpoint heads of the sperm cells - at highest resolution.

[ Batillipes male, detail ]

Batillipes tardigrade male. Detail of hind body. Transmitted light.

In the meanwhile we have been able to detect freely deposited Batillipes eggs. But this will be subject of a later issue.


Hartmut Greven: Die Bärtierchen. p. 44. Neue Brehm-Bücherei, vol. 537, Lutherstadt Wittenberg 1980 [last revised edition].

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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