(355MGmin) Megalothorax minimus (Willem 1900)


*normani (Collinge & Shoebotham, 1909)

Megalothorax minimus is a very common and widespread blind species with a highly characteristic appearance (Figs. 1,2, and 3). Although it is tiny (maximum length 0.5 mm), careful examination of the underside of rotting wood and leaf litter with a hand lens will often reveal specimens walking along with a gait that reminds me of a tiny old man hunched in a baggy coat.
The empodium of the foot is about half as long as the claw (Fig. 4) and the third (ant3) and fourth (ant4) antennal segments are not clearly separate (Fig. 5). The edges of the mucro are smooth (Fig. 6), and the sensory field on the abdomen (Fig. 7) is bordered by five marginal setae (Fig. 8).

There is a single record for Megalothorax incertus, from the ECOTRON experiment at Silwood Park (Naeem et al.,1994). The source of the specimens was not stated, and there is some doubt as to whether Megalothorax incertus is a good species, or is simply a variety of Megalothorax minimus. Bretfeld (1999) reported Megalothorax incertus as being from the dsoutern regions of Europe, and that the characters used to separate the species are variable (extent of serration of the mucro and length of projection at the base of the empodium), as well as difficult to resolve in such tiny springtails (maximum length of 0.5 mm). Even if Megalothorax incertus is shown to be a good species, there is no compelling evidence for including it on the UK/Eire checklist.

 

 

Fig. 1: Megalothorax minimus (arrow) of 0.25 mm in length under the head of Pogonognathellus longicornis in Steve Hopkin's garden in Reading.

Fig. 2: Megalothorax minimus of 0.35 mm in length in a garden in Reading. The specimen appears to have been grazing on green algae. The four 'compartments' of the gut are clearly visible through the cuticle (cf. Fig. 3)

Fig. 3: Megalothorax minimus collected from Lamorna Cove, Cornwall in April 1955 by T. Clay. Note the four 'compartments' of the gut (arrows).

Fig. 4: Feet of the first and third legs of Megalothorax minimus collected from Parliament Hill Fields, London in December 1952 by D.S. Murphy.

Fig. 5: Terminal part of the antenna of Megalothorax minimus collected from Tringford Reservoir in February 1964 by Peter Lawrence.

Fig. 6: Furca of the same specimen of Megalothorax minimus shown in Fig. 5.

Fig. 7: Abdominal sensory organ (seen in profile) of the same specimen of Megalothorax minimus shown in Fig. 4).

Fig. 8: Abdominal sensory organ of the same specimen of Megalothorax minimus shown in Fig. 5. The sensory organ is surrounded by five setae (1 to 5).

 
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