Dichaetophora ancora (Okada) Grimaldi, 2023

Grimaldi, David A., 2023, A remarkable species of drosophilid fly (Diptera) with “ mandibles ”, American Museum Novitates 2023 (4005), pp. 1-12 : 2-9

Dichaetophora ancora (Okada) , new combination

Drosophila (Psilodorha) ancora Okada, 1968: 334 .

Drosophila (Drosophila) ancora Okada : Yassin 2013 (synonymy of s.g. Psilodorha with s.g. Drosophila )

DIAGNOSIS: Distinguished from other species in the genus by frons and face broad, frons very short; facial carina well developed but short; prescutellar setae present; genal setae stout, sizes nearly equal to vibrissa; anterior reclinate orbital seta lateral to proclinate ( figs. 1 ; 3A, B ); wing with heavy costal spinules extended to tip of vein R 4+5; tip of male wing more pointed than in female (cf., fig. 2D, E ); aedeagus with two hornlike, preapical lateral spines pointed posteriad and one dorsomedial spine retrorse to axis of aedeagus ( fig. 3F, H ); male with labellar sclerites heavily sclerotized, dorsal portion extended into apically pointed lobes that form pair of “mandibles” ( figs. 1 ; 3A ; 4A, B ).

REDESCRIPTION: Coloration ( figs. 1 , 2 ): Head unicolorous dull, light brown; carina, flagellomere 1, oral margins slightly lighter; gena dark yellow; palps brown; eyes pale red; male labellar sclerites dark, shiny brown; all setae black. Notum dull brown, with pair of faint, incomplete, paramedian lighter stripes; notopleural area, anepisternum and katepisternum slightly darker than surrounding areas; halter knob cream colored; femora light brown, remaining leg segments yellowish; wing clear, no infuscation even around crossveins. Abdomen lighter than rest of body, dark yellowish, grading posteriorly to light brown.

HEAD ( fig. 3A, B ): Carina well developed, short, height carina/face 0.55; edge flattened but narrow; oral margin of face slightly swollen; frontal W-index 2.42. Frons short, FL/LFW 0.53, UFW/LFW 1.29; frontal triangle reaching ptilinal suture; frontal vittae narrow, dull, finely striate; fronto-orbital plates and frontal triangle slightly shiny. All setae robust, thick, black; anterior reclinate fronto-orbital seta relatively large, OR 2 /OR 1 0.77, lateral to proclinate, posterior reclinate is longest fronto-orbital, OR 1 /OR 3 0.62. Ocellar setae large, OC/POC 1.38, sockets within ocellar triangle; postocellars cruciate for ~0.25x their length. Verticals and postgenal setae robust, VT index 1.12. Antenna: pedicel and flagellomere 1 aligned ~30° outward from vertical; pedicel with five stout setae, several smaller ones, longest seta on ventromedial corner (length equal to flagellomere 1); microtrichia on flagellomere 1 short; arista with 6 or 7 dorsal, 2 or 3 ventral branches (exclusive of terminal fork). Vibrissa stout and long; genal setae on ventral margin of head are stout, sizes approximately equal to vibrissa, vibrissa index GS1/VL 1.10. Cheek very shallow, cheek/eye depth 0.07, gena deep, setose. Eye with dense ommatrichia, ED/EW 1.32; posteroventral margin flattened.

MOUTHPARTS ( fig. 4A, B, D ): Clypeus shallow, narrow. Cibarium very constricted closest to proximal end (shaped like a bowling pin); hypopharynx flared at proximal end (array of very fine muscle scars developed, broad and flat for most of distal end; dorsal keel present but barely sclerotized; long row of 23 or 24 short sensilla trichodea lateral to hypopharynx in middle, lateral to these a finely granular area; cibarium distally with row of 7 longer sensilla trichodea. Palp dorsoventrally asymmetrical but broad, with 2 large apical setae and 2 smaller ventral setae. Lacinia with distal arm very slender; proximal arms opposing each other 180°, one about twice the width of other. Prementum with ventral swelling. Labellum with each lobe having five pseudotracheae of equal diameters, proximally these converge in a pair of dark sclerites (“pseudotracheal sclerites”) at base of the labellum. Slender lateral labellar sclerite articulating with, apparently not fused to, the apical labellar sclerite; apical sclerites with broad ventral portion, in males there is a pair of dorsal, heavily sclerotized lobes with pointed apices, which in frontal view resemble biting mandibles. Female lacks the “mandibles” (pointed lobes of apical labellar sclerite).

THORAX ( figs. 1A , 2A , 3C ): Mean length 1.28 mm; relatively broad and short in dorsal view, width 0.77× its length (including scutellum). Postpronotal lobe with two setae of nearly equal size, h-index 1.19. Acrostichals not arranged in even rows, increasing in size from anterior to posterior; transverse row of three or four acrostichals anterior to transverse suture are slightly enlarged. Two large pairs of dorsoventrals present, DC-index 0.66, posterior pair slightly convergent, anterior pair slightly divergent; anterior to each are two smaller dorsoventrals; pair of prescutellar setae present, 0.45× the length of posterior dorsocentral. Scutellum without setulae; anterior and posterior scutellar setae approximately equal in length, scut-index 0.90, posterior pair crossing for about 0.2× their length. Scutum extended considerably ventrolaterally; notopleural suture near middle of depth of thorax. Anepisternum relatively large; katepisternum relatively small, with large anterior and posterior setae (nearly equal in size, S-index 0.89), small middle seta less than half the length of others, ~10 setulae on ventral portion of katepisternum. Hind leg: mesal surface of basitarsomere with row of nine combs of fine setulae, each comb with 5–7 setulae, the combs oblique to axis of tarsomere (2 or 3 smaller combs on adjacent tarsomeres); row or seam of ~30 cuneiform setulae along entire ventral margin of basitarsomere ( fig. 2C ).

WING ( fig. 2D, E ): Mean length 2.73 mm; clear, no markings; shape slightly dimorphic: tip of male wing pointed, that of female more rounded. C-index 1.77; costal spinules black, crowded, extend to tip of wing (R 4+5) (hb-index 1.0), vein C ends at apex of vein M 1+2. Sc break deeply incised. 4-V index 1.86; 5-X index 1.13.

Abdomen: Tergites mostly dark yellow, grading gradually to light brown posteriad.

MALE TERMINALIA ( fig. 3D–H ): Epandrium tall, narrow, fully covered with microtrichia; small cluster of ~10 setulae on short ventral lobe, setulae lacking on most of epandrium. Remnants of tergite 7 very small. Cercus relatively simple (no ventral lobes or spines), fully covered with microtrichia, without broad lateral connection to epandrium. Surstylus relatively broad, bare except a few sparse microtrichia, mesal row of six small, stout, pointed prensisetae; with narrow dorsal connections to cercus and bridge to other surstylus. Subepandrial sclerite broad, with pair of rounded lobes. Genitalia relatively simple; hypandrium without microtrichia, having pair of deeply incised postgonite lobes, each with large lateral setula and two small trichodea on mesal margin. Aedeagus nearly straight, apex with pair of lateral hornlike, sclerotized lobes/spines pointed apicad, plus median point having very fine papillae on dorsal surface; dorsally with a preapical, median, sclerotized spine pointing anteriad. Aedeagal apodeme short, straight, length 0.4× that of aedeagus. Ejaculatory apodeme relatively large, lightly sclerotized; surface against ejaculatory bulb is concave. Ejaculatory bulb without diverticula.

FEMALE TERMINALIA ( fig. 4E, F ): Tergite 7 mostly covered in microtrichia, no setulae; posteroventral portion declivous. Epi- and hypoproct apically narrow; covered with microtrichia and setulae. Oviscapt well developed: in ventral view anterior end broad, posterior end narrow; posteriorly with apical pair of fanglike lobes that curve outward, base of each with fine setula; laterally with two small pegs, each on short tubercle; two additional small, preapical pegs dorsally. Ventrally with irregular row of 19 or 20 very small, spiculelike pegs near mesal margin of each valve. Scales of oviprovector membrane very fine. Spermathecal capsule small, dome shaped, with introvert extended about halfway into capsule.

SPECIMENS: VIETNAM: Quang Nam, 25 km SW Tam Ky, 15°11′39″ N, 108°2′37″ E, 940 m, 12–17/IV/1999, D. Grimaldi, coll. 1 male, in American Museum of Natural History ( AMNH). Not dissected. Ninh Binh Prov. Cuc Phuong Nat. Park, 390 m, 20°21′103″ N, 105°35′36″ E [12-9], SD Gaimari, M Hauser, Pham HT, 24–28.III.2012, Malaise trap (terminalia and mouthparts dissected), 1 male, in Institute of Ecology and Biological Resources ( IEBR), Hanaoi; Cao Bang Prov. Phia Oac Nat. Park , nr. Phia Den. 1000 m, 22°32′20″ N, 105°51′57″ E [12-01], SD Gaimari, M Hauser, Pham HT, 19.III.2012 (terminalia dissected), 1 female, in AMNH .

COMMENTS: Dichaetophora ancora is known from the Ryukyus, Japan (type locality: Iri-omote Island; also reported from Kume Island [ Kondo and Kimura, 2008]); Taiwan and Hainan Island ( Kai et al., 1993). Masanori Toda informs me that the specimen referred to as “sp. 8 Malaysia ” in the preprint by Katoh et al. (2021) is Di. ancora or a very closely related species.

ffle two male Vietnam specimens may belong to a different species, since they show differences with the drawings of the type by Okada (1968: 335) and photomicrographs of specimens from the type locality sent to me by Toda (which are very consistent with each other). Definitive ancora , from Japan, have a male wing that is less pointed, and have the following differences in the male terminalia: longitudinally longer epandrium (i.e., not as broad in lateral view), cercus smaller, hypandrium that is significantly broader; aedeagal apodeme with broad, fanlike apex (though not so broad in the illustration of the type); pair of lateral, preapical phallic horns that are smaller, protruding less; and the dorsal spine of the phallus projecting upright, perpendicular to the axis of the aedagus (rather than being reclined as in the Vietnam specimens) .

Okada (1968) mentioned acrostichals in 10–12 rows, but which in the Vietnam specimens are not arranged in rows. Remarkably, the male “mandibles” were not mentioned in the original description, even though Okada was an excellent morphologist (Toda confirms their presence in the material from the type locality). Until the type male is dissected (presumably it is in the National Science Museum, Tokyo, where Okada typically deposited new types), it is best to regard the Vietnam specimens as Dichaetophora ancora .

ffle three Vietnamese specimens come from different areas, but there is no doubt in associating the female with the males, based on thorax- and abdomen-coloration patterns, distinctive proportions of the head, proportions of the various setal lengths and wing veins, carina shape, strong bristles on the oral margin, costal spinules running to the end of R 4+5, and various other features.

RELATIONSHIPS: Distinctive features of Di. ancora include the short frons, anterior reclinate lateral to the proclinate, stout setae on the pedicel, numerous large setae along the oral margin, numerous sensilla trichodea in the proximal group on the cibarium (23–24, vs. 4–~ 15 in Drosophila ), and of course the male “mandibles.” Dissection of the female specimen revealed an egg with four fine, tapered filaments (their lengths slightly less than that of the egg), as occur in many drosophilines. Prescutellar setae occur in steganines and sporadically in drosophilines (many Scaptodrosophila , scattered Drosophila , etc.). Costal spinules that end at the wing tip is a very distinctive feature (usually they end approximately midway between the tips of R 2+3 and R 4+5). Given such a unique array of features, it isn’t surprising that Okada (1968) erected for it the Drosophila subgenus Psilodorha . Also, at the time there was a much narrower concept of Dichaetophora . Clearly, however, Di. ancora does not belong in the subgenus Drosophila , as proposed by Yassin (2013), despite the diphyletic nature of the subgenus ( Finet et al., 2021), nor can it even be accommodated in the genus Drosophila , based on the structure of epandrium, male genitalia, cibarium, and oviscapt.

Oviscapt structure is the most obvious feature that places Di. ancora in Dichaetophora sensu lato (this includes Nesiodrosophila , some Lordiphosa [ Hu and Toda, 2002], Mulgravea and the subgenus Dudaica of Drosophila [ Katoh et al., 2018, 2021]). Other features that Di. ancora shares with Dichaetophora are on the cibarium: anterior end of hypopharynx expanded, anterolateral corners only slightly protruded (usually with a pair of hornlike lobes, the cornua), and the large number of sensilla trichodea. In the sinensis group there can be>40 medial cibarial sensilla per side ( Hu and Toda, 2002, 2005), but the number is generally less (in Dudaica there are only about 12–15).

Also shared with some Dichaetophora are five pseudotracheae on each labellar lobe (e.g., acutissima group, in other groups there are four); and a surstylus bare of microtrichia (e.g., tenuicauda group) ( Hu and Toda, 2005). A short, broad carina occurs in the Dichaetophora trilobita species group ( Yang et al., 2017) and some others, as well as in Dudaica . Most other species in the genus (e.g., agbo group) have a face that is almost flat with a low carina. A small number (~4–7) of stout, small prensisetae with pointed tips is a common feature in Dichaetophora .

fflere are, however, features of Di. ancora that differ with Dichaetophora : ocellar setae not outside the triangle, costal spinules extended to the wing tip, a pair of strong prescutellar setae, and large genal setae on the oral margin. Based on the short frons, carina shape, eye shape, and male genitalia (with a distinctive pair of gonite lobes as in Dudaica ), D. ancora may be in or near the clade consisting of the acutissima group and Dudaica ( Katoh et al., 2018, 2021). ffle molecular phylogeny of Katoh et al. (2021) indicated two groups (parts “1” and “2”) with undescribed species, to which Di. ancora also might belong. ffle classification and taxonomy of genera now being included in an expanding Dichaetophora ( Mulgravea , D. [ Dudaica ]) will need to be addressed, including the possibility that some of the earliest branches become separate genera.

In the collections from Vietnam are two females also from Cuc Phuong, but of a closely related species. fflese females have a darker thorax (scutellum slightly velvety), frons slightly pruinose blue, face light, abdominal tergites with dark bands (interrupted in middle), and the deep subcostal incision is slightly darkened on both sides of the break. Otherwise, this species shares the same distinctive features with the female of Di. ancora ; it will be very interesting to eventually find the male of this other species and to examine the males of some other Dichaetophora .

Figures

FIG. 1. Dichaetophora ancora (Okada) A–D: Male, from Vietnam (Quang Nam) A. Lateral habitus. B. Head, lateral. C. Head, frontal. D. Male mouthparts, frontal view. E. Female mouthparts, frontal view.

FIG. 3. Somatic and male genitalic structures of Di. ancora. A. Male head, frontal view. B. Male head, lateral view. C. fflorax, dorsal. D. Epandrium with cerci and surstyli. E. Detail of surstylus. F. Male genitalia, ventral view. G. Ejaculatory structures. H. Aedeagus, oblique lateral view. A and B; D and G; F and H to same scales. Abbreviations: ad, aedeagus; ads, anterior dorsocentral seta; aro, anterior reclinate orbital seta; c, carina; ce, cercus; dl-als, dorsal lobe of apical labellar sclerite (“mandibles”); ds, dorsal spine of aedeagus; e, epandrium; eja, ejaculatory apodeme; ejb, ejaculatory bulb; ejd, ejaculatory duct; gs, genal setae; hy, hypandrium; ls, lateral spine of aedeagus; oc, ocellar seta; p, palp; prs, prescutellar setae; sr, surstylus; v, vibrissa.

FIG. 2. Di. ancora. A–D: Male (same specimen as in fig. 1). A. fflorax, dorsal. B. Abdomen, dorsal. C. Right hind tarsus, mesal view. D. Wing. E. Female wing tip. F. Oviscapt, ventral.

FIG. 4. Mouthparts and female terminalia of Dichaetophora ancora (A, B, D–G) and labellum of Drosophila immigrans (C). A. Male proboscis, lateral view. B. Male labellar sclerites, front view. C. Labellum of Drosophila immigrans, lateral view. D. Cibarium of Di. ancora, ventral view. E. Oviscapt, ventral. F. Oviscapt, tergite 7 and paraprocts, spermatheca, lateral view. G. Hypothesized function of male “mandibles,” in ventral view. Stippled portions are tip of female oviscapt. A–D: to same scale. Abbreviations: als, apical labellar sclerite; cl, clypeus; dl-als, dorsal lobe of apical labellar sclerite (“mandibles”); lc, lacinia; lls, lateral labellar sclerite; ms, medial sensilla of cibarium; ov, oviscapt; p, palp; pt, pseudotracheae; pts, pseudotracheal sclerite; vmls, V-shaped medial labellar sclerite.