(358 BOarv) Bourletiella arvalis (Fitch, 1863)

*lutea (Lubbock, 1867)

Bourletiella arvalis is a widespread and common species. It is yellowish in colour. The empodium of the foot is shorter than the claw and bears a separate filament. The subanal appendages of the female are paddle-shaped when viewed from above. In the males, the thick setae on the sixth abdominal segment (abd6) all point in a posterior direction (Fig. 1) (cf. Bourletiella hortensis in which these thick setae point in opposite directions). Almost all the records for Bourletiella arvalis have been under the name Bourletiella lutea which is now regarded as a junior synonym of Bourletiella arvalis.

This is very close to Bourletiella viridescens, a more montane species whose occurrence in the UK is likely but remains unproven. In male Bourletiella viridescens, the thick setae in the abdominal organ (on abd6) are of different sizes (anterior pair longer than posterior pair) whereas they are all of similar size in Bourletiella arvalis (Fig. 1). In female Bourletiella viridescens, the subanal appendages are supposed to be broader in comparison to their length than in Bourletiella arvalis.

 

 

 

Fig. 1: Sixth abdominal segment (abd6) of a male specimen of Bourletiella arvalis collected from Jeallotts Hill, Berkshire in July 1967 by Peter Lawrence. The thick setae are of similar size and all point towards the posterior.

 
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