Scatellini Wirth and Stone

Zatwarnicki, Tadeusz & Mathis, Wayne N., 2024, Revision of the Nearctic Species of the Shore-Fly Genus Scatophila Becker (Diptera: Ephydridae), Zootaxa 5487 (1), pp. 1-100 : 6-8

Tribe Scatellini Wirth and Stone

Scatellini Wirth and Stone 1956: 466 . Type genus: Scatella Robineau-Desvoidy1830 .— Olafsson 1991: 55–68 [relationships among Palearctic genera].— Mathis & Zatwarnicki 1995: 254–288 [world catalog].

Diagnosis.—Specimens of Scatellini may be distinguished from other Ephydridae by the following combination of character states: Body length 0.80–5.00 mm; generally dark brown to cinereous (rarely yellow), microtomentose to shiny.

Head: Mesofrons subquadrate, slightly wider posteriorly, ranging from dull and densely microtomentose, to shiny with metallic luster; lacking interfrontal setae; usually 2 lateroclinate, fronto-orbital setae (most genera) or 1 ( Limnellia , Scatophila ). Antenna relatively short; arista essentially bare, macropubescent (most genera) or bearing long dorsal rays ( Philotelma ); pedicel with a row of setae along anterior margin, setae longer ventrally plus 1 proclinate and 1 vertical seta dorsally. Face protuberant, setulose to moderately densely pilose, marginal setae usually larger; dorsum of interfoveal hump usually similar to rest of face, dark colored in a few species, not shiny; eye bare, usually as long as high, nearly round to obliquely oval, generally oriented obliquely to plane of epistoma; gena short to high, usually bearing a genal seta (most genera) or lacking ( Haloscatella , Lamproscatella , Philotelma , Thinoscatella ); oral opening moderately large, gaping, usually concealing clypeus; maxillary palpus long and slender; mediproboscis with small sclerite laterally ( Scatella , Thinoscatella ); labellum not overlapping the mentum posteriorly.

Thorax: Dorsocentral setae 2–3 (0+2, 1+2), some setae sometimes weakly developed, the posteriormost seta displaced laterally from alignment of others; postpronotum sometimes with 1 long setae (Parascatella); row of small intra-alar setae present; intrapostalar seta small, weakly developed; presutural supra-alar seta present, variable, subequal or larger than anterior notopleural seta; postsutural supra-alar seta smaller than postalar seta or subequal in length (Parascatella); 2 notopleural setae, placement of posterior seta variable, usually at same level as anterior seta; proepisternum lacking setae but often with a few setulae (Parascatella); prosternum bare of setae or setulae; anepisternum bearing 1 large seta just dorsad of midheight along posterior margin, several smaller setulae may also be present; anepimeron, meron, and metapleuron bare of setae. Wing hyaline to conspicuously infuscate with or without white spots; costal vein extended to vein M 1 (most genera) or to vein R 4+5 ( Scatophila ); crossvein r-m just posteriorly to distinctly distal to subcostal break ( Haloscatella [species from New Zealand], Philotelma , Limnellia , Scatophila ) vein R 2+3 usually long, terminating at approximately same distance from vein R 4+5 as tip of M 1 vein is from vein R 4+5. Hindcoxal strap not setose; pulvilli normally developed; tarsal claws short, curved.

Abdomen: Male with 5 visible abdominal tergites; tergite 5 distinctly trapezoidal or triangular; sternites 5–6 well developed, very small or absent; female with 7 visible tergites; tergite 5 subtrapezoidal, not triangular. Male terminalia: surstylus usually fused with ventral margin of epandrium and not evident (most genera) or evident as lobes, perhaps secondarily developed; aedeagus usually a sclerotized structure, shoe-shaped (apparently the basiphallus) ( Amalopteryx Eaton , Haloscatella [other than New Zealand species], Lamproscatella , Limnellia , Scatella , Scatophila , Thinoscatella ) or with a sclerotized basiphallus and a membranous distiphallus invested with short, sharp scales or scale-like thorns (some Haloscatella [species from New Zealand], Philotelma ); ejaculatory apodeme lacking ( Amalopteryx , Haloscatella , Lamproscatella , Limnellia , Philotelma , Scatophila , Thinoscatella ) or present (as an L-shaped, dorsoventrally flattened structure or a crescent shaped, laterally flattened structure) (Apulvillus Malloch, Parascatella Cresson, Scatella Robineau-Desvoidy , Synhoplos Lamb, Teichomyza Macquart); phallapodeme rudimentary, as a laterally flattened bow ( Lamproscatella , Haloscatella [other than New Zealand species]) or rod-like, lacking a keel ( Amalopteryx , Haloscatella [ New Zealand species], Limnellia , Philotelma , Scatophila ) or greatly reduced or lacking (Apulvillus, Parascatella, Scatella , Synhoplos, Teichomyza); postgonites and hypandrium fused forming a single structure (“gonal arch”) ( Amalopteryx , Haloscatella , Lamproscatella , Thinoscatella , Apulvillus, Parascatella, Scatella , Synhoplos, Teichomyza, ground plan of Limnellia ) or separated into medial sclerite “hypandrium” and lateral structures representing postgonites ( Philotelma , New Zealand Haloscatella , most Scatophila ) or separated medioventrally into 2 lateral structures “gonites” (most Limnellia ) (2 separate postgonites are present also in some Scatophila (avida group), in which the “hypandrium” is reduced). Female Terminalia: sternite 7 as one rectangular sclerite or 2 lateral, small, circular to partially quadrate sclerites; sternite 8 divided into 2 sclerites; cerci bearing one prominent seta, strong or weak, inserted posteroventrally or without prominent setae; sternite 9/subanal plate without strong setae; operculum present or absent, when present Helmet-like or tubular shaped.

Discussion.— Scatophila belongs to the Philotelma group of genera ( Zatwarnicki and Mathis 1994). Species of the Philotelma group (genera Philotelma , Tauromima , Limnellia , and Scatophila ) are very tiny to moderately small shore flies (body length 0.80–2.50 mm), males have a broken ventral gonal arch and the anterior portion of the epandrium is fused, forming a complete cavity around the cerci. The ventral gonal processes are all that remains of the hypandrium, which is fused anterodorsally to the postgonites ( Figs. 19 , 28 , 54 , 123 , 173 ). The fusion of postgonites and hypandrium was first described in the genus Dimecoenia Cresson ( Steyskal 1970) , and Olafsson (1991) assumed this condition to be characteristic of Ephydrinae . According to Zatwarnicki (2023), the subfamily Ephydrinae should be expanded to include the tribe Hyadinini , and as such, all included tribes within this subfamily have postgonites that are associated with the hypandrium. Three tribes of Ephydrinae have the central portion of the hypandrial arch narrowed and band-like. The medial portion of the hypandrium has been separated, and for this separated structure, we proposed the term neohypandrium ( Zatwarnicki and Mathis 1994). Zatwarnicki and Baéz (1991) were not entirely accurate in calling this structure the hypandrium, as it is only a portion of the latter. The division of the gonal arch and presence of a neohypandrium are synapomorphies that link the genera Scatophila and Philotelma . The lack of these structures in Limnellia and some Scatophila may have occurred secondarily, as is perhaps manifested by the medially separated gonal arch in these taxa.

Within the Philotelma group, the genus Philotelma has many autapomorphies: 1. postgonite without ventral process, 2. aedeagal sack present, 3. crossvein dm-m infuscate, 4. genal seta lacking, but the presence of dorsal aristal hairs distinguish this genus from the remaining genera, all of which have reduced aristal hairs or rays. The genus Tauromima has reduced wings and halteres and only one dorsocentral and subscutellar seta. The monophyly of Limnellia and Scatophila is confirmed by the (1) multicolored mesonotum and (2) modified, band-like or reduced neohypandrium.

The known species of Scatophila and Limnellia have a single fronto-orbital seta, and for that reason these two genera were treated as sister groups. We have discovered a Neotropical species group, the prainha group that have a shortened costa but have two fronto-orbital setae. Three explanations may account for this condition: (1) the loss of one fronto-orbital seta occurred independently in Scatophila and Limnellia ; (2) Limnellia is a specialized sublineage within Scatophila ; (3) the occurrence of two setae in a few South American species is a secondary development. Both Limnellia and Scatophila are characterized by synapomorphies that suggest their monophyly and independent evolution, i.e., one genus is not a sublineage of the other (alternative 2). Synapomorphies for Limnellia are: (1) presence of epandrial processes (surstyli, which are not homologous to dististyli) and (2) dark spots on the wings.

Our study of the South American species with two fronto-orbital setae has revealed other characters that are likely to represent generalized or primitive states. Assuming these primitive conditions are correlated with the presence of two setae, we suspect that alternative three is likewise untenable, leaving, thus, the first alternative as the most likely explanation.

Synapomorphies that characterize Scatophila (short costa, extended only to vein R 4+5, and narrow band-like neohypandrium) may not be universal to all congeners. Brachyptery in two species, for example, precluded confirmation of a short costa (character 8). Synapomorphies of the male genitalia are also not common to all species of Scatophila , with some species having the band-like neohypandrium reduced. The monophyly of the genus is thus confirmed by a suite of complex characters that are complementary to each other.

Figures

FIGURES 18–20. Male terminalia of Scatophila exilis Cresson. 18. Epandrium and cerci, posterior view. 19. Internal male terminalia (gonite, phallapodeme, aedeagus, neohypandrium), ventral view. 20. Same, lateral view. Scale bar = 0.1.

FIGURES 27–29. Male terminalia of Scatophila angusta sp. nov. 27. Epandrium and cerci, posterior view. 28. Internal male terminalia (gonite, phallapodeme, aedeagus, neohypandrium), ventral view. 29. Same, lateral view. Scale bar = 0.1 mm.

FIGURES 53–55. Male terminalia of Scatophila hesperia Sturtevant & Wheeler. 53. Epandrium and cerci, posterior view. 54. Internal male terminalia (gonite, phallapodeme, aedeagus, neohypandrium), ventral view. 55. Same, lateral view. Scale bar = 0.1 mm.

FIGURES 122–124. Male terminalia of Scatophila unicornis Czerny. 122. Epandrium and cerci, posterior view. 123. Internal male terminalia (gonite, phallapodeme, aedeagus, neohypandrium), ventral view. 124. Same, lateral view. Scale bar = 0.1 mm.

FIGURES 172–174. Male terminalia of Scatophila conifera Sturtevant & Wheeler. 172. Epandrium and cerci, posterior view. 173. Internal male terminalia (gonite, phallapodeme, aedeagus, neohypandrium), ventral view. 174. Same, lateral view. Scale bar = 0.1 mm.