Pandinus imperator (C. L. Koch, 1841)

Farley, Roger D., 2011, Pectine development in scorpion embryos and first and second instars, Euscorpius 120 (120), pp. 1-47 : 7-8

Pandinus imperator ( Scorpionidae )

For the embryo of Figure 28, the outer wall of the appendix was opened, and the embryo was removed. The embryonic membrane was absent or dissected away so the embryo surface could be examined with the SEM. As in embryos of Hadogenes paucidens (Figs. 18, 20), the mesosoma is large and developed compared to the prosoma and metasoma. When early embryos are removed from the diverticulum and examined with the dissecting microscope, the digestive tract can be seen extending posteriorly from the mouth before any other organs and appendages appear. An appendix forms very early; its proximal end leads directly to the anterior end of the digestive tract when the embryo is only an elongate tube of cells with a digestive tract inside ( Mathew, 1956). That basic and early structure is still evident in Figure 28 except that the mesosomal segments have large dorso-lateral processes.

No segments can be discerned in the prosoma and metasoma of Figure 28, but the mesosomal segments are distinct with the large dorso-lateral lobes on each segment. No prominent limb buds are evident on the ventral surface of the mesosoma, though some small wrinkles or lobes may be indicative of limb buds. There is no apparent indication of pectinal formation.

The embryo of Figure 29 was removed from the diverticulum and is more advanced than the embryo in Figure 28. Some prosomal appendages are evident in Figure 29, but there is still no indication of chelicerae or pectines. Apparently, the chelicerae will differentiate from the lobe of tissue (Lo) in the anterior part of the prosoma. There are no prominent limb buds in the ventral mesosoma, though there are some small lobes that may be indicative of limb buds (Fig. 30). Collapsed dorso-lateral processes are present on the mesosomal segments, and some faint indications of segments can be discerned in the metasoma. As in the embryo of Figure 28, the appendix leads directly to the prosoma where there is apparently a mouth and anterior digestive tract.

The ventral mesosoma of the embryo of Figure 29 is shown at higher magnification in Figure 30. The genital operculum and pectines will eventually form just posterior to the fourth leg (Fig. 32), but the tissues in this region in Figure 30 still show little indication of the structures that will form. Some small lobes are labeled in the ventral mesoma as possible traces of limb buds (LB).

Figure 31 shows mesosomal segments 6 and 7 of an embryo more advanced than those in Figures 28 − 30. The features in Figure 31 look much like those at a similar stage in embryos of Hadogenes paucidens (Figs. 23 − 25) where spiracles and sternites are starting to appear on the ventral surface. The prominent setae (bristles, B) in Figure 31 appear to precede the formation of the sternites. They are in a pattern that outlines the flap-like form of the sternites before the sternites appear. The asterisks indicate setae just inside the initial creases (Ste) that are the first indication of sternite formation. The setae in Figure 31 are about 130 µm in length while those of H. paucidens are about 80 µm in Figure 25.

The initial steps in formation of the genital operculum and pectines were not seen in this species, but these structures are evident in a more advanced stage in Figure 32. The setae (bristles, B) at this stage appear to be deteriorating. They are much less prominent than in Figure 31, although the flap-like sternites are more distinct on the ventral surface of the mesosomal segments. The pectines are attached only at their proximal ends, and they have distinct anterior and posterior regions with a row of teeth at the posterior edge. Some invaginations that appear to be primordial spiracles are labeled in the figure.