An abnormally developed embryo of the pill millipede Glomeris marginata that lacks dorsal segmental derivatives

Intraspecific variation and phylogeography of the millipede model organism, the Black Pill Millipede Glomerismarginata (Villers, 1789) (Diplopoda, Glomerida, Glomeridae)

The Black Pill Millipede, Glomerismarginata, is the best studied millipede species and a model organism for Diplopoda. Glomerismarginata is widespread, with numerous colour morphs occurring across its range, especially in the south. This study investigates whether colour morphs might represent cryptic species as well as the haplotype diversity and biogeography of G.marginata. The results of the COI barcoding fragment analysis include 97 G.marginata, as well as 21 specimens from seven potentially related species: G.intermedia Latzel, 1884, G.klugii Brandt, 1833 (G.undulata C.L. Koch, 1844), G.connexa Koch, 1847, G.hexasticha Brandt, 1833, G.maerens Attems, 1927, G.annulata Brandt, 1833 and G.apuana Verhoeff, 1911. The majority of the barcoding data was obtained through the German Barcode of Life project (GBOL). Interspecifically, G.marginata is separated from its congeners by a minimum uncorrected genetic distance of 12.9 %, confirming its monophyly. Uncorrected intraspecific distances of G.marginata are comparable to those of other widespread Glomeris species, varying between 0–4.7%, with the largest genetic distances (>2.5 %) found at the Mediterranean coast. 97 sampled specimens of G.marginata yielded 47 different haplotypes, with identical haplotypes occurring at large distances from one another, and different haplotypes being present in populations occurring in close proximity. The highest number of haplotypes was found in the best-sampled area, western Germany. The English haplotype is identical to northern Spain; specimens from southern Spain are closer to French Mediterranean specimens. Analyses (CHAO1) show that approximately 400 different haplotypes can be expected in G.marginata. To cover all haplotypes, it is projected that up to 6,000 specimens would need to be sequenced, highlighting the impossibility of covering the whole genetic diversity in barcoding attempts of immobile soil arthropod species.

A curious abnormally developed embryo of the pill millipede Glomeris marginata (Villers, 1789)

This paper reports on an abnormally developed embryo (ADE) of the common pill millipede Glomeris marginata. This ADE represents a modified case of Duplicitas posterior, in which two posterior ends are present, but only one anterior end. While the major posterior germ band of the embryo appears almost normally developed, the minor posterior germ band is heavily malformed, has no clear correlation to the single head, little or no ventral tissue, and a minute amount of yolk. The anterior end of the minor germ band is fused to the ventral side of the major germ band between the first and second trunk segment. At least one appendage of the second trunk segment appears to be shared by the two germ bands. Morphology and position of the minor germ band suggest that the ADE may be the result of an incorrectly established single cumulus [the later posterior segment addition zone (SAZ)]. This differs from earlier reports on Duplicitas posterior type ADEs in Glomeris marginata that are likely the result of the early formation of two separate cumuli.

Developmental abnormalities in Glomeris marginata (Villers 1789) (Myriapoda: Diplopoda): implications for body axis determination in a myriapod

Abnormally developing embryos (ADEs) of the common pill millipede Glomeris marginata have been investigated by means of nuclear staining and mRNA in situ hybridization. It showed that all ADEs represent cases of Duplicitas posterior, which means that the posterior body pole is duplicated. The severity of the duplication ranges from duplicated posterior trunk segments in one specimen to an almost completely duplicated specimen that only shares the very anterior head region. Remarkably, none of the encountered ADEs represents a case of Duplicitas anterior (duplicated anterior pole) or a case of Duplicitas cruciata (cruciate duplication with two anterior and two posterior poles). This observation is discussed in the light of earlier reports on G. marginata ADEs that claim to have found these abnormalities. The lack of any other axial abnormality aside from D. posterior implies that early axis determination in G. marginata, and possibly myriapods in general, underlies the developmental mechanisms that prevent the formation of any other type of axial duplication. It is proposed that the formation of D. posterior-type embryos could be caused by the formation of two instead of only one posterior cumulus early during development.