(382AHpri) Arrhopalites principalis (Stach, 1945)

All members of the genus Arrhopalites have only one ocellus on each side of the head. Arrhopalites principalis is a scarce species found inside and outside caves. The empodium of the foot is slightly longer than the claw (Fig. 1) and the fourth antennal segment (ant4) is divided into six clearly defined subsegments (Fig. 2). Both the inner and outer edges of the mucro are serrated (Fig. 3).  The female sub-anal appendage is 'feather shaped' in Arrhopalites principalis (Fig. 4), and there are six thickened setae on each side of the dorsal region of the head (Fig. 5).

Arrhopalites cochlearifer can be mentioned here, as it is  very similar in appearance to Arrhopalites principalis but has only one confirmed UK record.  However, whereas there are only four thickened setae of the same size on each side of the dorsal region of the head of Arrhopalites cochlearifer (Fig. 6) compared to six on the head of Arrhopalites principalis (Fig. 5).  In addition,  the female sub-anal appendage is 'feather shaped' in Arrhopalites principalis (Fig. 4) but  'spoon shaped' at the tip in Arrhopalites cochlearifer. (fig. 7).

 

 

 

Fig. 1: Foot of the third leg of Arrhopalites principalis collected from Salen, Mull, Scotland in June 1970 by Peter Lawrence.

Fig. 2: Antenna of the same specimen of Arrhopalites principalis shown in Fig. 1. The fourth antennal segment (ant4) is clearly subdivided into six subsegments (1 to 6).

Fig. 3: Distal furca of the same specimen of Arrhopalites principalis shown in Fig. 1. Both the inner and outer edges of the mucro are serrated.

Fig. 4: Female sub-anal appendages (SAA) of the same specimen of Arrhopalites principalis shown in Fig. 1. The tip is 'feather' shaped.

Fig. 5: Dorsal region of the head of the same specimen of Arrhopalites principalis shown in Fig. 1. There are six thick setae (1 to 6) on each side of the head (only one side visible).

 

Fig. 6: Dorsal region of the head of Arrhopalites cochlearifer collected from Roudsea Wood, Lancashire in September 1962 by Peter Lawrence. The specimen is damaged but here are clearly only four thick setae (1 to 4) on each side of the head.

Fig. 7: Female subanal appendage (SAA) of the same specimen of Arrhopalites cochlearifer shown in Fig. 6. The tip is 'spoon' shaped and is clearly not feathered.

 
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