(057/FRtru) Friesea truncata (Cassagnau, 1958)

Friesea truncata is a bluish-grey moderately common and widespread soil-dwelling species with three, occasionally four (Fig. 1), or five anal spines. It was formerly known as Friesea mirabilis var. reducta. The largest specimen I have seen is 1.2 mm in length. Friesea truncata does not possess clavate setae and a mucro is absent from the dens (Figs. 2, 3, 4; this is the main feature which separates it from Friesea mirabilis). In fact, several specimens labelled Friesea 'mirabilis' in the NHML collection are Friesea truncata which is obviously more common and widespread than has hitherto been realised. 

Some authors use chaetotaxy to separate Friesea mirabilis from Friesea truncata. Friesea mirabilis has been described as having seta a4 PRESENT on the dorsal side of the second thoracic segment (th2) whereas in Friesea truncata, seta a4 is ABSENT from th2. In Friesea mirabilis, seta A4 is supposed to be PRESENT on the tibiotarsi whereas in Friesea truncata seta A4 is ABSENT. However, these characters are not 100% reliable in UK/Eire material; asymmetry is frequent. The possibility still exists that Friesea truncata is simply a variety of Friesea mirabilis. 

Species of Friesea have 8+8 ocelli but no post-antennal organ (PAO absent) or empodium on the foot.

 

 

Map Friesea truncata
Anal spines of Friesea trucata

Fig. 1 : Anal spines (*) on the sixth abdominal segment (abd6) of Friesea trucata collected from Epping Forest in May 1951 by J.T. Salmon. There are three 'normal' anal spines (*) and an additional spine (*arrow). D, dorsal; V, ventral.

Furca of Friesea truncata

Fig. 2 : Furca of Friesea truncata collected from Tarlton, Glos. in April 1970 by Harold Gough. There is no mucro on the dens. Ant, anterior; man, manubrium; Post, posterior; ten, tenaculum.

Furca of Friesea truncata

Fig. 3 : Furca of Friesea truncata collected from Boreat, Northants. in February 1968 by Harold Gough. There is no mucro on the dens. Ant, anterior; man, manubrium; Post, posterior. The tenaculum is out of the plane of focus.

Furca of Friesea truncata

Fig. 4 (above): Furca of the same specimen of Friesea truncata shown in Fig. 1. There is no mucro on the dens. Ant, anterior; man, manubrium; Post, posterior; ten, tenaculum.

 
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