Xenylla welchi is a scarce bluish species which reaches 1.0 mm in length. All the records are from English cultivated mushroom beds, glasshouses (growing cucumbers), and compost heaps. Thus it may be an old introduction rather than a native member of our Collembola fauna. The mucro is separate from the dens and bears a prominent lamella (Figs. 1 and 2). The tenaculum has 3+3 teeth (Fig. 3). Another useful character is the presence of only one clavate tenant seta on the outer side of the tibiotarsus of the first leg (leg1) which I have seen in all the specimens I have examined (Fig. 4). Legs2 (Fig. 5) and legs3 have two clavate tenant setae in this position. This helps to distinguish it from the similar Xenylla mucronata which has two clavate tenant setae on the outer side of the tibiotarsus of leg1. Also, the positions of setae p1 and p2 on th2 differ between the species. In the NHML collection, there are several specimens labelled Xenylla mucronata but these are all Xenylla welchi and are mapped as such here. There are no definite records of Xenylla mucronata from Britain and Ireland.
Fig. 1 (above): Ventral view of the furca of Xenylla welchi collected from cultivated mushrooms at Minehead, Somerset in July 1934 by F. Laing. The dens and mucro are clearly separate (*). man, manubrium.
Fig. 2 (above): Ventral view of the furca of Xenylla welchi shown in Fig. 1. The dens and mucro are clearly separate (*). The mucro has a prominent lamella and a 'notch' (n) at the tip.
Fig. 4 (above): Leg1 of the same specimen of Xenylla welchi shown in Fig. 1. There is only one clavate tenant seta (*) on the dorsal side of the tibiotarsus.
Fig. 3 (above): One side of the tenaculum of the same specimen of Xenylla welchi shown in Fig. 1. There are three teeth (*) on the side in focus.
Fig. 5 (above): Leg2 of the same specimen of Xenylla welchi shown in Fig. 1. There are two clavate tenant setae (*) on the dorsal side of the tibiotarsus.
