Rev: 11/19/2019

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Trischistoma Cobb, 1913


Tripylina Brzeski, 1963 is considered an invalid synonym

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Morphology and Anatomy:

In Trischistoma, the females are monovarial, prodelphic and the whorls of six outer labial and four cephalic setae are well separated (Andrassy, 2007; Cid del Prado et al., 2010; and Cid del Prado et al., 2016).

In the genus Tripylina Brzeski, 1963 (family Trischostomatidae), the outer labial and cephalic whorls of six and four setae are close together, almost in a single whorl (Tsalolikhin 1983; Zullini 2006; Cid del Prado-Vera et al. 2010; 2012).



Cuticle smooth, sometimes with setae.

Three conical lips, each with 2 papillae, not set off from body contour.

Outer labial and cephalic setae in two whorls, separated from each other, 6 in the first and four in the second.

Stoma narrow with dorsal tooth and small stomal denticles; can open wide to ingest prey.

Trischistoma has a single gonad, a smooth cuticle, small stomal denticles  and the whorls of setae separated; and DEGO at tip of buccal tooth.

Esophagus cylindrical with three glands overlapping intestine.

Monovarial, prodelphic, with or without post-uterine sac.

Caudal glands open through spinneret at tail tip.




Rare.  Supplements anterior to cloaca.

Occur in some species.

Body size range for the species of this genus in the database - Click:

Key to Trischistoma species (from Cid del Prado et al., 2016)

1. Body a tight spiral shape after death.T. helicoformis n. sp.

    Body not spiral-shaped after death..2

2. Post-uterine sac present......................3

    Post-uterine sac absent....................7

3. Body length > 2.0 mm......4

    Body length < 2.0 mm....5

4. Body length 2.9-3.2 mm; tail length 220-242 µm.T. subtillissimum Andr�ssy, 2011

    Body length 4.0-4.1 mm; tail length 250-260 µm...T. tenuissimum  Andr�ssy, 2011

5. Male absent; V = 75%; tail length 81-98 µm.. T. otaika Zhao, 2011

    Male present; body length 1.0-1.9 mm.�6

6. Body length 1.4-1.9 mm; a = 45-77; female tail length 115-150 µm, spicules 25-35 µm long; male tail with one supplement. T. monohystera (de Man, 1880) Schuurmans-Stekhoven, 1951

    Body length 1.4-1.6 mm; a = 38-44; V = 81-83%; female tail length 80-96 µm;  spicules 40-44 µm long; male tail with 2-3 supplementsT. equatoriale Andr�ssy, 2006

    Body length 1.0-1.3 mm; a = 41-54; female tail length 63-104 long; spicules 29-34 µm long� T. veracruzense Cid del Prado-Vera, Ferris & Nadler, 2010

    Body length 1.0-1.1 mm; a = 49-53; c = 12-13, female tail length 82-86 µm; spicules 25-32 µm long� T. gracile Andr�ssy, 1985

7. Body length < 1.0 mm.....8

    Body length > 1.0 mm..10

8. Body length 0.4-0.6 mm; female tail length 40-50 µm�T. minor Tahseen & Nusrat, 2010

    Body length 0.6 -0.9 mm; V = 73-80%......9

9. Cervical setae absent; pharynx length 155 µm; tail length 50-60 µm; b = 4.4-4.8�T. pellucidum Cobb, 1913

    Single latero-ventral cervical setapresent; pharynx length 171-198 µm; tail length 50-64 µm �T. waiotama Zhao, 2011

    Paired lateral cervical setae present; pharynx length 137-219 µm; tail length 44-72 µm. T. triregius Zhao, 2011

10. Body length 0.80-1.2 mm; a = 34-45; V = 67-73%; female tail length 51-84 µm.....     . T. corticulensis n. sp.

    Body length 1.0-1.1 mm; a = 39-59; female tail length 34-92 µm...11

11. a = 45-59; c = 17-29; b = 4.1-4.8; V = 67-73%; female tail length 34-57 µm� T. ripariana n. sp.

    a = 39-47; c = 11-15; b = 3.8-4.1; V = 72-76%; female tail length 75-92 µm � T. tukorehe Zhao, 2011



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Moist soils with organic material and on tree and rock surfaces associated with mosses and lichens..

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Predators of small organisms, including nematodes (Yeates et al., 1993; Cid et al., 2010).

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Biology and Ecology:


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Life Cycle:

For Ecophysiological Parameters for this genus, click 
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Ecosystem Functions and Services:

Predation and population regulation of prey species.

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Copyright © 1999 by Howard Ferris.
Revised: November 19, 2019.