(243.5ACthe) Archisotoma theae (Fjellberg, 1980)

Archisotoma theae is a tiny (0.5 mm) rare littoral species described by Fjellberg in 1980. While examining slides labelled 'Archisotoma' in the NHML slide material, Steve Hopkin found a single specimen of Archisotoma theae collected by Peter Lawrence from Studland Heath, Dorset in November 1963. It has probably been overlooked elsewhere. The body is greyish-brown in colour, a PAO is present and the eyes each have eight ocelli. Like Archisotoma besselsi, Archisotoma theae has a thick spur-like seta above the claw on the tibiotarsus of leg 3.
Diagnostic characters include ventral tube with 4+4 setae (Fig. 1) and dens with six dorsal setae (Fig. 2) and four ventral setae (Fig. 3).

 

 

 

Fig. 1: Ventral tube (VT) of Archisotoma theae collected from Studland Heath, Dorset in November 1963 by Peter Lawrence. There are four lateral setae (*) (visible on one side only).

Fig. 2: (See also Fig. 3) Two levels of focus of the furca of the same specimen of Archisotoma theae shown in Fig. 1. The dorsal side of the dens (Fig. 2: above left) has six setae (*) and the ventral side (Fig. 3: above right) has four setae (*).man, manubrium.

Fig. 3: Two levels of focus of the furca of the same specimen of Archisotoma theae shown in Fig. 1. The dorsal side of the dens (Fig. 2: above left) has six setae (*) and the ventral side (Fig. 3: above right) has four setae (*).man, manubrium.

 
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