Namibimydas psamminos, Dikow, T., 2012

Dikow, T., 2012, Review of Namibimydas Hesse, 1972 and Nothomydas Hesse, 1969 (Diptera: Mydidae: Syllegomydinae: Halterorchini) with the description of new species, African Invertebrates 53, pp. 79-111 : 89-92

Namibimydas psamminos sp.n.

Figs4-6, 17, 18, 43

ZooBank LSID:see Table1.

Etymology:From Greek psamminos (of sand),referring to the apparent distribution along the eastern edge of the Namib desert sand dunes.

Diagnosis:The species is distinguished from congeners by the short proboscis that does not extend beyond the fronto-clypeal suture,the short and sparse abdominal setation in both males and females(Figs17, 18),and its apparent distribution at the eastern edge of the Namib Desert sand dunes in Namibia(Fig.43).

Description:

Male.

Head:Black,in general grey pubescent;width distinctly greater than thorax,interocular distance on vertex larger than at ventral eye margin,vertex between compound eyes more-or-less horizontally straight,medially only slightly below dorsal eye margin,parafacial area about as wide as half the width of central facial gibbosity;facial gibbosity distinct,well-developed and discernible in lateral view;mystax white,covering entire facial gibbosity;frons entirely grey pubescent,vertex entirely grey pubescent,postgena apubescent;setation:vertex white or yellow,frons white or yellow,ocp setae white,pocl macrosetae yellow;ocellar triangle apubescent;proboscis brown,short,about half length of oral cavity;labellum small,as wide as prementum,about half length of prementum,unsclerotised laterally;maxillary palpus cylindrical,light brown,as long as pedicel.

Antenna:Brown,scape and pedicel white setose dorsally and ventrally;postpedicel cylindrical in proximal0.4,symmetrically bulbous in distal0.6,≥4.0 × as long as combined length of scape and pedicel;apical ‘seta-like’ sensory element situated apically in cavity on postpedicel.

Thorax:Brown,predominantly grey pubescent;scutum uniformly brown,surface entirely smooth,lightly grey pubescent,broad sublateral stripes(interrupted postsuturally)and narrow paramedial stripes(not reaching posterior margin)darker grey pubescent,scutal setation comprised of long white setae with distinct rows of long dorsocentral setae and dense lateral scutal setae;dc setae pre- and postsuturally white,acr setae present,lateral scutal setae white,npl setae0,spal setae0,pal setae0;postpronotal lobe light brown,grey pubescent;proepisternum,lateral postpronotum,and postpronotal lobe long white setose;scutellum grey pubescent,asetose,apical scutellar setae absent;mesopostnotum,anatergite,and katatergite grey pubescent,mesopostnotum asetose,anatergite long white setose,katatergite long white setose;katatergite more-or-less flat;anterior anepisternum asetose,supero-posterior anepisternum long white setose;posterior anepimeron long white setose,katepimeron long white setose;metanepisternum grey pubescent,asetose,metepimeron more-or-less flat,same colour as T1,grey pubescent,long white setose.

Leg:Light brown,setation predominantly white;pro,mes,and met coxa lightly grey pubescent,long white setose;met trochanter setose medially;femur light brown,met femur more-or-less cylindrical only slightly wider than pro and mes femur,in distal half macrosetose,1anteroventral and1posteroventral row of macrosetae,posteroventrally sparse long white,erect setose and setae arranged in distinct row;pro,mes,and met tibia straight,met tibia cylindrical,ventral keel absent,lateroposteriorly sparse long white,erect setose and setae arranged in distinct row;pro and mes tarsomere1longer than tarsomere2,but less than combined length of tarsomeres2-3,met tarsomere1as long as combined length of tarsomeres2-3;pulvillus well-developed,as long as well-developed claw,and as wide as base of claw;empodium absent.

Wing:Length 14.6-15.9mm;hyaline throughout,veins light yellow,microtrichia absent;cells r1,r4,r5,m3,and cup closed;C terminates at junction with R1;R4terminates in R1;R5terminates in R1;stump vein(R3)at base of R4present,short not reaching R2;R4and R5widest apart medially; r–m distinct,R4+5and M1apart,connected by crossvein;M1curves slightly anteriorly at r–m,M1(or M1+M2)terminates in R1;CuA1and CuA2split proximally to m–cu (cell m3narrow proximally);M3+CuA1do not terminate together in C;A1undulating,cell a1wide,A1and wing margin further apart proximally than distally;alula well-developed,very large and partly overlapping with scutellum medially;haltere light brown.

Abdomen:Brown and light brown;setation comprised of dense short white setose,surface entirely smooth;T1brown,yellow posterior margin,T2-3light brown,anteriorly brown and posteriorly with yellow margin,T4-7light brown with yellow posterior margin;T1and anterior half of T2long white setose,remaining T short white setose;T1apubescent,T2-7grey pubescent;S1-7light brown;S1asetose,S2-7sparsely white setose;S predominantly apubescent;T2-4parallel-sided and not constricted waist-like;bullae on T2black,oval,surface entirely smooth,T2surface anterior to bullae smooth.

Terminalia(Figs4-6):Supra-hypandrial sclerite present.

Female.

Head:Brown,vertex and frons white setose.Antenna:Postpedicel≥5.0 × as long as combined length of scape and pedicel.Wing:Length 15.5-17.1mm.Abdomen:T1brown,T2-7brown with yellow posterior margin.Genitalia:5-6acanthophorite spines per plate.

Holotype:♂ NAMIBIA: Hardap: Namib-Skeleton Coast National Park,Sesriem, Elim Dune , 24°27'28"S 15°46'37"E, 826m,vegetated dune,resting on dead vegetation+sand, 9.ii.2012, T.Dikow (AAM-007360, NMNW) .

Paratypes: NAMIBIA: Erongo: 1♂ Homeb, 16km ESE Gobabeb (23), 23°38'12"S 15°10'55"E, 23-25.i.1972, BMNH Southern Africa Expedition (AAM-000867, BMNH) . Hardap: 1♀ Sesriem 137, 24°29'00"S 15°48'00"E, 5-8.iv.1972 (AAM-003056, NMNW) ; 2♂ 2♀ Namib-Skeleton Coast National Park , Sesriem, Elim Dune , 24°27'28"S 15°46'37"E, 826m,vegetated dune,resting on dead vegetation+sand, T.Dikow, 9.ii.2012 (AAM-007361-AAM-007364, NMNW, USNM) ; 1♂ Namib-Skeleton Coast National Park , Sesriem, Elim Dune , 24°27'35"S 15°46'21"E, 839m,vegetated dune,resting on dead vegetation+sand, 10.ii.2012, T.Dikow (AAM-007365, USNM) .

Type locality and distribution:Namib-Skeleton Coast National Park,Elim Dune near Sesriem(24°27'28"S 15°46'37"E),Namibia(Fig.43,GBIF resource#14003).Not known to occur in any biodiversity hotspot.

Remarks:This species has been labelled previously as a new species and as a holotype by J.Bowden(unpublished)who named it Mesomydas syncrasis based on the male from Homeb deposited in the BMNH (see image at Morphbank#704382,note:♂terminalia previously removed).Since neither the generic nor the specific name have ever been published,they have no standing in nomenclature.Bowden was apparently unaware that the specimen he studied was congeneric with Namibimydas ,which might be because this species,in contrast to all other known Namibimydas species,has a short proboscis and Hesse(1972)in describing the genus highlighted the fact that the proboscis is long.

At the start of this project only two specimens of this new species were known,i.e.,the Homeb specimen referred to above and the Sesriem♀ paratype (see image at Morphbank,#704386).Througheld work conducted by myself in February2012,eight specimens(six listed above plus one male preserved in95%ethanol and one male in Kahle’s)were collected on the partly vegetated sand dune named Elim Dune in the Namib-Skeleton Coast National Park(24°27'28"S 15°46'37"E,habitat in Fig.45)near Sesriem.Theflies were flying very fast during the period between9:00a.m.to1:00p.m.(I did not visit this same dune in the afternoon)and were difficult to catch.I estimate that I only caught every fourth specimen I saw often after a prolonged chase with the fly very seldom interrupting its flightpath.The males were more active and appeared to fly from one vegetated hummock to another one in search for females.When a female,which were observed to rest close to the base of the plants in the shade,were encountered by the males both of themflew high into the air and could not be followed anymore.The flight behaviour of the males was very similar to aculeate Hymenoptera who often have a sustained,meandering flight low above the surface.The species was not encountered on a similarly vegetated dune some 18.5km further SW along the road to Sossusvlei(24°36'17"S 15°40'10"E, 780m)that was visited shortly after a series of specimens had been collected at Elim Dune.