Review of Namibimydas Hesse, 1972 and Nothomydas Hesse, 1969 (Diptera: Mydidae: Syllegomydinae: Halterorchini) with the Description of New Species

ABSTRACT The Mydidae genera Namibimydas Hesse, 1972 and Nothomydas Hesse, 1969 are reviewed. Both genera were known from two species each occurring in southern Namibia and western South Africa and are here redescribed. Four new species, all from Namibia, are described herein: Namibimydas psamminos sp. n., Namibimydas stuckenbergi sp. n., Nothomydas aquilonius sp. n., and Nothomydas picketti sp. n. A dichotomous key to all species is presented and illustrations and photographs are provided to support the descriptions and future identification. Distribution, occurrence in biodiversity hotspots sensu Conservation International, and seasonal incidence are discussed for all species. Information of all four genera of Syllegomydinae: Halterorchini is summarised and photographs of all genera provided. A novel structure of the male terminalia, termed supra-hypandrial sclerite, is described and illustrated.


INTRODUCTION
The southern African Mydidae fauna is the most diverse world-wide both in terms of species numbers and generic diversity. A.J. Hesse's (1969) seminal work on the southern African mydids, in which he described no fewer than 108 new species (106 of which are still valid) and 12 new genera (11 of which are still valid), provided a comprehensive overview of this unique fauna. In a few publications following this extensive work (Hesse 1972(Hesse , 1974(Hesse , 1975, he added another 17 new species and 3 new genera. Earlier, Gerstaecker (1868) and Bezzi (1924) studied the then available region. Stuckenberg (1955Stuckenberg ( , 1966 added to the knowledge of southern African Mydidae by describing one of the largest species, Afroleptomydas omeri (Stuckenberg, 1955) (Syllegomydinae), and one of the most enigmatic species, Tongamya miranda Stuckenberg, 1966 (Megascelinae). The genus Tongamya Stuckenberg, 1966 was initially described in Apioceridae, the sister group of Mydidae (Yeates & Irwin 1996;Irwin & Wiegmann 2001;Dikow 2009), but transferred together with Megascelus Philippi, 1865 from Chile and Neorhaphiomidas Norris, 1936 from Australia to the Mydidae by Yeates & Irwin (1996).
This study reviews the genera Namibimydas Hesse, 1972 andNothomydas Hesse, 1969 placed in Syllegomydinae: Halterorchini, a tribal taxon established by Hesse (1972) who highlighted the morphological similarity of these two genera to Halterorchis Bezzi, 1924 andMimadelphus Hesse, 1972. These four genera are represented by few specimens in collections (see below) and new material from several collections, particularly the Namibian National Museum in Windhoek, makes this review, new distributional information of the two genera, and the description of four new species possible.
Namibimydas and Nothomydas. However, photographs of representatives of Halterorchis and Mimadelphus  are provided for reference.
It should be noted that the delimitation, phylogenetic relationships, and the monophyly of Halterorchini has not been tested to date. However, the author is currently preparing a morphological phylogeny of Mydidae world-wide and representatives of both Namibimydas and Nothomydas are included in this analysis (Dikow in prep.).

MATERIAL AND METHODS
Morphological terminology and abbreviations for setae follow McAlpine (1981), Stuckenberg (1999), Cumming &Wood (2009), andDikow (2009) except for the term 'aedeagal epimere', which is used as described by Hesse (1969). Abdominal tergites are abbreviated in the descriptions with 'T', and sternites are abbreviated with 'S.' The terms prothoracic, mesothoracic, and metathoracic are abbreviated 'pro', 'mes', and 'met', respectively. The term pubescence (adjective 'pubescent') refers to the short, the Torre-Bueno Glossary of Entomology (Nichols 1989). The species descriptions are based on composites of all specimens and not exclusively on the holotype and are compiled from a character matrix of 148 features assembled with Lucid Builder (version 3.5) and eventually exported as natural language descriptions. When available, species are fully described in the male sex while females are only described with those features that differ. The structure of the male terminalia and female genitalia is only described should be interpreted from the drawings. potassium hydroxide (KOH) at 55°C followed by neutralisation in acetic acid and ringlycerine and attached to the specimen's pin. The male terminalia of the holotype of Nothomydas aquilonius sp. n. had been macerated for too long several years ago and were stained in Chlorazol Black in order to darken the cuticle. Morphological features were illustrated using a 10×10 ocular grid on a Olympus SZ60 stereo microscope and later digitally converted to vector graphics using Adobe Illustrator software. The setation on male terminalia is not shown. Wing length was measured from the tegula to the distal tip of the wing. Photographs of pinned specimens were taken with a Olympus E-30 digital SLR, a 50 mm macro lens (equivalent of 100 mm focal length in 35 mm photography), and a 25 mm extension tube. The specimens were illuminated by a LED deposited in Morphbank::Biological Imaging and permanent links to the full-size imathe Encyclopedia of Life and available under the respective species page.
In recording data for type specimens as well as non-type specimens, information is given (where available) in a standard manner, i.e., locality, geographic co-ordinates, elevation, date of collection (month indicated in lower case Roman numerals where hyphens indicate missing entries for day, month, year), habitat information, sampling protocol (if other than hand netting), collector, and depository. Each specimen is listed with a unique AAM specimen number that will allow the re-investigation as well as distribution map with all localities plotted, for which co-ordinates were available, and the type locality is plotted with an open symbol. The specimen occurrence data are available on GBIF as data-set #14003 (persistent URL http://data.gbif.org/datasets/ resource/14003/ from Conservation International (2005; http://www.conservation.org/Documents/ cihotspotmap.pdf). The electronic key was deposited in the IdentifyLife archive and is also available at http://www.mydidae.tdvia.de/online_keys. All taxon names were registered in ZooBank (Pyle & Michel 2008; see Table 1).
Institutions providing specimens are listed below, together with the abbreviations used in the text when citing depositories, and the people who kindly assisted:

TAXONOMY
The 25 genera of southern African mydids cannot be distinguished reliably based studied representatives of all genera and I am working on a new key for the forthcoming Manual of Afrotropical Diptera (Dikow in prep.), the scope of this manuscript does not allow for inclusion of a key to separate the Halterorchini genera from others. All Halterorchini genera are illustrated with colour photographs in this article to allow future Namibimydas and Nothomydas share a number of unique characteristics, particularly the male terminalia are distinctive, which are not known from other Syllegomydinae to date. In addition to the generic diagnoses, the following features are present in males of both taxa (Figs 10, 32): (1) abdominal sternite 8 strongly sclerotised and pointing ventrally (perpendicular to antero-posterior axis), (2) abdominal tergite 8 laterally elongated, sometimes partly overlapping with gonocoxite-hypandrial complex, (3) gonocoxite-hypandrial complex antero-dorsally with a unique bilobed sclerite (ventral to subepandrial plate) here termed supra-hypandrial sclerite (see Discussion), and (4) aedeagus with two thin and elongate prongs.
Wing: Length 13.8-15.2 mm; hyaline throughout, veins light yellow, microtrichia absent; cells r 1 , r 4 , r 5 , m 3 , and cup closed; C terminates at junction with R 1 ; R 4 terminates in R 1 ; R 5 terminates in R 1 ; stump vein (R 3 ) at base of R 4 present, short not reaching R 2 ; R 4 and R 5 widest apart medially; r-m distinct, R 4+5 and M 1 apart, connected by crossvein; M 1 straight at r-m (not curving anteriorly), M 1 (or M 1 +M 2 ) terminates in R 1 ; CuA 1 and CuA 2 split proximally to m-cu (cell m 3 narrow proximally); M 3 +CuA 1 do not terminate together in C; A 1 undulating, cell a 1 wide, A 1 and wing margin further apart proximally than distally; alula well-developed, very large and partly overlapping with scutellum medially; haltere light brown.
Terminalia (Figs 1-3): Supra-hypandrial sclerite absent (see Remarks). Female. Thorax: Scutum predominantly grey pubescent, broad sublateral stripes (interrupted postsuturally) and narrow paramedial stripes (not reaching posterior margin) apubescent. Wing: Length 15.0-17.7 mm. Abdomen: Scattered white setose; T1 and anterior half of T2 long white setose, remaining T short white setose; bullae on T2 black, small and circular. Genitalia: 6-7 acanthophorite spines per plate. Type locality and distribution: Walvis Bay (22°57'27"S 14°30'19"E), Namibia (Fig. 43, GBIF resource #14003). Not known to occur in any biodiversity hotspot. Remarks: When Hesse (1972) studied the specimens from the SMNS on which he based the new species description, he apparently did not study the female from Sandwichhafen also deposited in the SMNS. This specimen was studied by myself in October 2010 during a visit to the SMNS. The absence of a supra-hypandrial sclerite in this species is quite surprising. It is possible that this sclerite has been fused with the dorso-lateral margin of the gonocoxite-hypandrial complex and therefore forming a "roof" closing this structure dorsally (Fig. 1).
The species was recently collected at the Swakop River mouth by myself and observed One specimen was collected resting on dead, grey vegetation low above the ground Namibimydas prinsi Hesse, 1974 Figs 10-12, 15, 16, 43 Namibimydas prinsi : Hesse 1974: 26. ZooBank LSID: see Table 1. Diagnosis: The species is distinguished from congeners by the lack of ventral macrosetae on the metathoracic femora, the short abdominal setation in females (Fig. 16), and its apparent distribution in coastal habitats in the far south-western Western Cape Province of South Africa (Fig. 43).

Redescription:
Male. Head: Black, in general densely grey pubescent; width distinctly greater than thorax, interocular distance on vertex larger than at ventral eye margin, vertex between com-pound eyes more-or-less horizontally straight, medially only slightly below dorsal eye margin, parafacial area more than half 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 lightly grey pubescent; setation: vertex white, frons white, ocp setae white, pocl macrosetae light brown; ocellar triangle apubescent; proboscis brown, long, projecting well-beyond fronto-clypeal suture, reaching half length of postpedicel; labellum small, as wide as prementum, about quarter length of prementum, unsclerotised laterally; maxillary palpus cylindrical, light brown, as long as pedicel.
Terminalia (10-12): Supra-hypandrial sclerite present. Female. Head: Pocl macrosetae yellow; labellum about 0.2 length of prementum. Antenna: Leg: met femur posteroventrally sparse long white, erect setose and setae arranged in distinct row; met tibia lateroposteriorly sparse long white, erect setose and setae arranged in distinct row; met tarsomere 1 less than combined length of tarsomeres 2-3. Wing: Length 12.3-12.7 mm; M1 straight at r-m (not curving anteriorly). Abdomen: Setation dense, very short white setose; T1-7 brown; T1 and antero-lateral corners of T2-3 long white setose, remaining T short white setose; S1-7 predominantly asetose; bullae on T2 black, oval. Genitalia: 6-7 acanthophorite spines per plate.  Namibimydas psamminos sp. n. 17,18, 43 ZooBank LSID: see Table 1. 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 (Figs 17,18), 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.
Terminalia : Supra-hypandrial sclerite present. 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 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, Morphbank, #704386 the Namib-Skeleton Coast National Park (24°27'28"S 15°46'37"E, habitat in Fig. 45) estimate that I only caught every fourth specimen I saw often after a prolonged chase a female, which were observed to rest close to the base of the plants in the shade, were not encountered on a similarly vegetated dune some 18.5 km further SW along the road to Sossusvlei (24°36'17"S 15°40'10"E, 780 m) that was visited shortly after a series of specimens had been collected at Elim Dune.
Namibimydas stuckenbergi sp. n. 19,20,43 ZooBank LSID: see Table 1. Etymology: The species is named after and dedicated to the memory of Diptera systematist and taxonomist Brian Roy Stuckenberg, who contributed in many great ways to Afrotropical dipterology (Kirk-Spriggs 2012). Diagnosis: The species is distinguished from congeners by the long proboscis that extends beyond the fronto-clypeal suture, but does not reach the tip of the postpedicel (Fig. 20), the entirely white mystax (Figs 19, 20), the long abdominal setation in both males and females, and its apparent distribution in coastal (or near coastal) habitats around Lüderitz in Namibia (Fig. 43). Description:

Male.
Head: Black, in general densely 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 less than 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 lightly grey pubescent; setation: vertex white, frons white, ocp setae white, pocl macrosetae yellow; ocellar triangle apubescent; proboscis brown, long, projecting well-beyond fronto-clypeal suture, reaching half of length of postpedicel; labellum small, as wide as prementum, about quarter length of prementum, unsclerotised laterally; maxillary palpus cylindrical, light brown, as long as pedicel.

Female.
Wing: Length 12.5-15.2 mm. Abdomen: Setation dense short white setose, T1 and anterior half of T2 long white setose, remaining T short white setose; bullae on T2 black, small and circular. Genitalia: 9 acanthophorite spines per plate.  ZooBank LSID: see Table 1. Diagnosis: The genus is distinguished from other Syllegomydinae by its small size with a wing length of 5.5-8.9 mm, the long proboscis that extends beyond the tip of the postpedicel, the entirely transparent wings, the slender legs, the anteriorly directed setae on abdominal tergites 4-8 in females, and structures of the male terminalia. Description:

Male.
Head: Black, in general densely 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 medially apubescent, laterally grey pubescent, vertex apubescent, postgena apubescent; setation: vertex white or yellow, frons white, ocp setae white or yellow, pocl macrosetae absent; ocellar triangle apubescent; proboscis brown, long, projecting well-beyond fronto-clypeal suture and beyond tip of postpedicel; labellum small, as wide as prementum, about quarter length of prementum, unsclerotised laterally; maxillary palpus cylindrical, brown, minute.

Supra-hypandrial sclerite in males
Species of Namibimydas (except N. gaerdesi, see below) and Nothomydas are unique in that the male terminalia possess an additional sclerite not found in other Syllegomydinae or even Mydidae. The supra-hypandrial sclerite (Figs 4,7,10,23,26,29,32) is a sclerite positioned dorsal to the proximal hypandrium and ventral to the subepandrial sclerite and is generally visible without dissection of the male terminalia in Nothomydas, but hidden by the epandrium in Namibimydas (sometimes visible in a posterior view). Hesse mentioned several unique features of the male terminalia for both Namibimydas and Nothomydas, but because he did not clear the hypopygia, he mistook the supra-hypandrial sclerite as the aedeagal epimere of Namibimydas prinsi Nothomydas gariepinus KOH it becomes apparent that the aedeagi in both genera are well-hidden within the gonocoxite-hypandrial complex and that the two prongs are thin and elongate (Figs 4,29). The supra-hypandrial sclerite is always bilobed apically and serrated and toothed The absence of an apparent supra-hypandrial sclerite in Namibimydas gaerdesi is quite surprising. It is possible that this sclerite has been fused with the dorso-lateral margin of the gonocoxite-hypandrial complex and therefore forms a "roof" closing this entire structure dorsally (Fig. 1).
The supra-hypandrial sclerite should not be confused with the subepandrial sclerite, which is situated immediately dorsal to it, is always weakly slcerotised and plate-like without any bifurcated tip, which continues distally into the hypoproct. There are other structures morphologically similar to the supra-hypandrial sclerite in the Oriental genus Cacatuopyga Papavero & Wilcox, 1974 (Cacatuopyginae) and the New World Mydinae. Papavero & Wilcox (1974: 14) mention a "grooved crest-like process" dorsally on the aedeagus of a Cacatuopyga Gauromydas mystaceus (Wiedemann, 1830) showing a process-like structure attached to the dorsoproximal aedeagal sheath, which is also visible in other Mydinae species illustrated by D'Andretta. The structures illustrated in these Cacatuopyginae and Mydinae might be visible when examining the uncleared male terminalia in lateral view and since they are directed dorsoposteriorly and approximate the subepandrial sclerite could be confused with the supra-hypandrial sclerite. However, these process-like structures are always attached to the aedeagus and neither to the hypandrium nor the gonocoxite. The Namibimydas and Nothomydas is attached dorsolaterally to the fused gonocoxite-hypandrial complex.

Seasonal incidence
All four species of Namibimydas have primarily been collected during January-February, during the Southern Hemisphere summer, while Na. psamminos sp. n. has also been collected in April (late summer) and Na. stuckenbergi sp. n. also in November (early summer). Species of Nothomydas have been collected from September-November, spring and early summer, with No. picketti sp. n. only occurring in September, No. gariepinus and No. namaquensis only in October, and No. aquilonius sp. n. only in November.

Biodiversity hotspots
The biodiversity hotspots sensu Conservation International (Myers et al. 2000) are areas of high plant endemism in which the habitat has been destroyed to a considerable extant and which are under threat of more destruction. Evaluating the presence/absence of Diptera species in these priority areas earmarked for conservation can de-