(242ACmeg) Archisotoma megalops (Bagnall, 1939)

*subbrucei Delamare Deboutteville 1954

Archisotoma megalops is a scarce littoral species, up to 2.5mm  (note the much larger size compared to Archisotoma besselsi), with an apparent northerly and eastern bias to its distribution. However, it may have been overlooked elsewhere. The body is blue/black to greyish in colour, a PAO is present and the eyes each have eight ocelli. Thibaud & Palacios-Vargas (2001) sunk Archisotoma subbrucei Delamare Deboutteville 1954 as a junior synonym of Archisotoma megalops. The definitive feature for identification is the structure of the maxilla (Fig. 1: compare this photo with Fig. 347 in Gisin (1960) of 'Archisotoma subbrucei' = Archisotoma megalops). The presence of an inner tooth on the claw is not a defining character as it is not reliably present (e.g. Fig. 2).

The mucro of Archisotoma is very distinctive with three large teeth (Figs. 3, 4).

 

 

 

Fig. 1: Maxilla (max) of Archisotoma megalops collected from Seaford in June 1946 by Bagnall.

Fig. 2: Foot of leg 3 of Archisotoma megalops from Boston, Lincolnshire collected in August 1952 (identity of collector unknown).

Figs. 3: (See also fig. 4) Two levels of focus of mucros of the same specimen of Archisotoma megalops shown in Fig. 2). The mucro has three large teeth.

Fig. 4: (see also fig. 3). Two levels of focus of mucros of the same specimen of Archisotoma megalops shown in Fig. 2). The mucro has three large teeth.

 
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