http://www.collembola.org/publicat/dicyrt.htm - Last updated on 2018.03.16 by Frans Janssens
Checklist of the Collembola: Note on the shape of the dorsal abdominal patch in Dicyrtomina ornata (Dicyrtomidae)

Frans Janssens, Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium
Marie Louise Huskens, Opitterkiezel 223 bus 0.1, B-3960, Opitter, Belgium

Abstract

Dicyrtomina ornata (Nicolet, 1842) has a distinct abdominal dorsal posterior patch. The shape of the patch is quite variable.

Introduction

Fig.Do. Dicyrtomina ornata.
Posterior dorsal patch on abd.4+5
Huskens, M.L. © 2017.11.01
In adults of Dicyrtomidae, the 5th abdominal segment, which is the genital segment, is fused with the 4th abdominal segment and as such incorporated within the large globular abdomen (Betsch, 1980:14). On the large abdomen, short spinelike setae are the centers of long thin wax tubes secreted by their tormogene cells (Bretfeld 1999:128). In Dicyrtomina ornata (Nicolet, 1842) both abdominal segments are pigmented with a middorsal dark patch. The patch on the 5th abdominal segment is kind of square in shape and is rather stable in form. The patch on the 4th abdominal segment is more rectangular in shape, is rather variable in form, and it marks the dorsal area in which wax 'glands' are situated. Both patches are joined into one middorsal rectangular solid patch on the posterior part of the large abdomen (Fig.Do).

Material and methods

Specimens of Dicyrtomina ornata were collected from the garden of the second author in Opitter, Limburg, Belgium. The specimens were collected with their habitat material. Observations were performed indoors on a staged set-up. Photographs were made using a digital reflex camera Canon EOS 80D. A Canon MP-E 65mm lens was mounted on the camera using a set of Kenko extension tubes (12mm + 20mm + 36mm). Illumination was provided by a Canon Macro Ring Lite MR-14EX and a Falcon Eyes SLP-120LTV LED lamp.

Results

The middorsal posterior patch is rather variable in shape. It can be narrow (Fig.Do1), broad (Fig.Do2), short (Do9), long (Fig.Do7), irregular (Fig.Do3). It can also be bipartite (Fig.Do8,Do15). It can be free from the lateral abdominal pigmentation (Fig.Do1,Do4,Do7), or connected to the lateral pigmentation (Fig.Do2,Do3,Do5). It is often bicoloured (dark central area and more pale lateral areas) (Fig.Do1,Do3,Do7,Do13).

Some examples of patch shapes.

Fig.Do1. Dicyrtomina ornata.
Posterior dorsal patch
Huskens, M.L. © 2017.11.01
Fig.Do2. Dicyrtomina ornata.
Posterior dorsal patch
Huskens, M.L. © 2017.11.02
Fig.Do3. Dicyrtomina ornata.
Posterior dorsal patch
Huskens, M.L. © 2017.11.16
Fig.Do4. Dicyrtomina ornata.
Posterior dorsal patch
Huskens, M.L. © 2017.11.23
Fig.Do5. Dicyrtomina ornata.
Posterior dorsal patch
Huskens, M.L. © 2017.11.01
Fig.Do7. Dicyrtomina ornata.
Posterior dorsal patch
Huskens, M.L. © 2017.11.01
Fig.Do8. Dicyrtomina ornata.
Bipartite posterior dorsal patch
Huskens, M.L. © 2017.10.20
Fig.Do9. Dicyrtomina ornata.
Short posterior dorsal patch
Huskens, M.L. © 2017.10.11
Fig.Do13. Dicyrtomina ornata.
Bicolour posterior dorsal patch
Huskens, M.L. © 2017.11.05
Fig.Do14. Dicyrtomina ornata juvenile.
Pale posterior dorsal patch
Huskens, M.L. © 2017.11.05
Fig.Do15. Dicyrtomina ornata.
Bipartite posterior dorsal patch
Huskens, M.L. © 2018.01.27

The dorsal posterior patch is composed out of the patch of the 5th abdominal segment and the patch of the 4th abdominal segment. The patch of the 5th abdominal segment is always present. The patch on the 4th abdominal segment is optional (Fig.Do9) and if present, quite variable in shape. Given the 5th abdominal segment is fused with the large abdomen, we consider the segment border between the 5th and the 4th abdominal segment defined by the absence versus presence of the abdominal wax 'glands' : present on the 4th abdominal segment, absent on the 5th.

Middorsal patch on 5th abdominal segment.
Fig.Do12. Dicyrtomina ornata.
Basic patch on 5th abdominal segment
Huskens, M.L. © 2017.11.05
Fig.Do12a. Dicyrtomina ornata.
Basic patch on 5th abdominal segment
modelled as 2 overlapping biconvex areas
Huskens, M.L. © 2017.11.05
The patch on the 5th abdominal segment can be modelled as being formed by two overlapping biconvex areas (Fig.Do12,Do12a).

Middorsal patch on 4th abdominal segment.

Wax producing tormogene cells.
Fig.Dotc. Dicyrtomina ornata.
Wax producing tormogene cells around short spinelike setae
Huskens, M.L. © 2017.12.06
Typically in Dicyrtomidae, on the posterior dorsal part, wax producing cells are situated. Posterior short spinelike setae are centers of long and thin wax secretions that are produced by their tormogene cells (modified after Bretfeld, 1999:128) (Fig.Dotc). The wax is extruded by the tormogene cell around the central seta and forms as such a narrow wax tube.

Raster of wax producing tormogene cells.
Fig.Dortc. Dicyrtomina ornata.
Raster of wax producing tormogene cells
Huskens, M.L. © 2017.12.06
Fig.Dortc2. Dicyrtomina ornata.
Raster of wax producing tormogene cells
Contrast enhanced negative image
Huskens, M.L. © 2017.12.06
The middorsal wax producing tormogene cells are present on the 4th abdominal segment, but absent on the 5th abdominal segment (Fig.Do6,Do10). They are arranged in an equidistant raster of minimum 8 x 9 wax cells (Fig.Dortc,Dortc2).

Raster of wax producing tormogene cells involved in the posterior middorsal patch.
Fig.Do6. Dicyrtomina ornata.
Pattern of wax producing tormogene cells
Huskens, M.L. © 2017.11.01
Fig.Do10. Dicyrtomina ornata.
Pattern of wax producing tormogene cells
Huskens, M.L. © 2017.09.20
The middorsal patch is situated around 2 middorsal longitudinal columns of 6 tormogene wax producing cells (Fig.Do6,Do10).
Fig.Do11. Dicyrtomina ornata.
Wax producing tormogene cells enlarged during moulting
Huskens, M.L. © 2017.12.06
Fig.Wr1. Dicyrtomina ornata.
Groundplan raster of wax producing tormogene cells of the 4th abdominal segment
Janssens, F. © 2017.12.03
During the moulting phase, the wax producing tormogene cells are distinctly enlarged (Fig.Do11). The wax 'glands' that participate in the middorsal patch are organised in an equidistant raster of 6 horizontal rows and 4 vertical columns (Fig.Wr1). The 6 horizontal rows, from top to bottom, count respectively 2-4-4-4-2-2 glands, and are designated Wg1 to Wg6.

Basic rectangular shape of dorsal patch.
Fig.Do10. Dicyrtomina ornata.
Basic rectangular patch
Huskens, M.L. © 2017.09.20
Fig.Mp1. Dicyrtomina ornata.
Simplified schematic model of basic patch of 4th abdominal segment
Janssens, F. © 2017.12.03
The basic shape of patch is rectangular, with a short more narrow top and a longer more narrow base (Fig.Do10). In the simplified schematic model, the patch is represented by 11 horizontal dark lines (Fig.Mp1). The lines are constrained in length by the positions of the wax 'glands'.

Rectangular patch with constricted base.
Fig.Do11. Dicyrtomina ornata.
Rectangular patch with constricted base
Huskens, M.L. © 2017.11.05
Fig.Mp2. Dicyrtomina ornata.
Simplified schematic model of patch with constricted base
Janssens, F. © 2017.12.07
The rectangular patch is often constricted at the base (Fig.Do2,Do11,Do13), at the level of row Wg4. In the simplified model, this is represented by a shortened horizontal dark line of the 4th row of wax 'glands' (Fig.Mp2).

Rectangular patch with multiple constrictions.
Fig.Do3. Dicyrtomina ornata.
Rectangular patch with multiple conctrictions
Huskens, M.L. © 2017.11.16
Fig.Mp3. Dicyrtomina ornata.
Simplified schematic model of patch with multiple constrictions
Janssens, F. © 2017.12.22
Multiple constructions at the level of row Wg2, Wg3 and Wg4 may give the patch a biserrate appearance (Fig.Do3) (Fig.Mp3). It can be confused with the multibarred patch of Dicyrtomina saundersi (Lubbock, 1862). But in D. saundersi the transverse bars are not equal in length.

Discussion

To be provided.

Conclusion

To be provided.

Bibliography