Pentachaeta McAlpine, 1985

McAlpine, David K., 2014, Review of the Australian Genus Pentachaeta (Diptera: Heleomyzidae), with Descriptions of Nine New Species, Records of the Australian Museum 66 (5), pp. 247-264 : 248-249

Pentachaeta McAlpine

Pentachaeta McAlpine 1985: 212–213 . Type species (original designation): P. physopus McAlpine.

For diagnostic description see McAlpine (1985). The genus is keyed among theAustralian heleomyzid genera by McAlpine (1985: 204–206) and McAlpine (2007: 155–156). The general coloration is distinctive for the genus: thorax largely pale tawny-orange with narrow brown longitudinal stripe on region of humeral callus and notopleuron; wing with one continuous broad brown anterior stripe covering entire costal margin and separate brown mark surrounding discal (posterior or dm-cu) cross-vein ( Fig. 1 ). These features, together with the following conditions of chaetotaxy make the genus easily recognisable among other Australian acalyptrate flies: single vibrissa strongly developed; postvertical bristles rather large, strongly convergent from bases; propleural (proepisternal) bristle large and isolated; mesopleuron (anepisternum) without setulae or bristles; dorsocentral bristles five large subequal pairs ( Fig. 2 ). Size range is indicated by a winglength of between 2.5 and 4.8 mm.

Male postabdomen

Within the genus Pentachaeta there is fairly consistent structure of the postabdominal parts (with a few exceptional conditions in some species) and some contrast with the structure so far observed in other heleomyzid tribes. The incompletely known Neotropical genus Dioche shows some agreement with Pentachaeta in hypandrial structure. The structure of the protandrium (the male postabdominal segments immediately preceding the genital segment) has been described for Dioche and Pentachaeta by McAlpine (1985). Other male postabdominal structures are here considered in more detail, but I do not here follow the terminology previously used for P. physopus ( McAlpine, 1985: 213, fig. 22).

The epandrium bears a pair of large surstyli, visibly articulated at the bases but usually not very freely so. In several species the inner basal surface of the surstylus has a group of stout setulae, and sometimes these are located on a basal prominence (e.g., Figs 5 ). The subepandrial cuticle is not markedly sclerotized except, in most species, for a distally setulose subepandrial process which arises on each side near the base of the surstylus. This is perhaps homologous with the “process of sternite 10” illustrated by Gill & Peterson (1987: figs 11,12) for a heleomyzine example, though differing in form. This structure was identified as “surstylus” by Gorodkov (1963: fig. 2b), who used the term “edita” for the processes usually termed surstylus or surstyle. It remains to be decided whether the subepandrial process in these heleomyzids is homologous with the anterior epandrial process occurring in some taxa of Helosciomyzidae and related sciomyzoid families (see McAlpine, 2012: fig. 14).

The hypandrium ( Fig. 3 ), with its associated structures, including the aedeagus, is very distinctive for the genus. The fork plate (Gabelplatte) consists of a pair of longitudinal sclerites, connected to each other anteriorly, and each narrowly connected posteriorly to a lateral sclerite bearing the gonostylus (postgonite). The gonostylus varies in shape but always bears a few elongate distal macrotrichia and sometimes a tuberculose distal zone. The basiphallus consists anteriorly of a pair of longitudinal sclerites, joined together anteriorly where they are attached to the aedeagal apodeme and posteriorly where they support the base of the distiphallus and bulb. The cuticle of the region of sternite 9 is recessed to form a pouch of which the basiphallus, the fork plate and the aedeagal apodeme contribute to the otherwise membranous lining, and into which the bulb can be withdrawn. The bulb is partly irregularly sclerotized and shows some variation in structure. In Pentachaeta impar n. sp. ( Fig. 36 ) the bulb possesses two broadly tubular structures with funnel-like openings. It is uncertain if these openings are functional gonopores, but in other species the gonopore appears to be located on the distal part of the section here identified as the distiphallus. Posteriorly on each side the basiphallus has an elongate, minutely densely pubescent extension, which is connected to the posterior extremity of the hypandrium by a compact articulating sclerite.

The cerci are approximated but not basally fused, large, elongate, strongly setulose at least in part and often partly microtrichose (fine microtrichia not shown in my illustrations), projecting anteriorly from the elongate attachment to the ventral surface of the tip of abdomen. They are of variable but often highly specific form.

Figures

Figure 1. Pentachaeta pinguis, northern form, female (13 km N of Ravenshoe).

Figure 2. Pentachaeta edwardsi. Dorsal view of thorax, showing chaetotaxy. dc, dorsocentral bristles (five pairs); hm, humeral bristle; ia, intra-alar bristle; np, notopleural bristles; pa, postalar bristle; ps, presutural bristle; sa, supra-alar bristle; sc, scutellar bristles.

Figure 3. Pentachaeta edwardsi. Hypandrial structures, ventral view (diagrammatic). aa, aedeagal apodeme; ab, aedeagal bulb; ag, aedeagal guide (connecting aedeagal apodeme to hypandrium anteriorly); as, articulating sclerite; dp, distiphallus; eh, sclerotized extension of hypandrium; fp, fork plate of hypandrium; g, gonostylus; mu, probable muscle attachment; pl, posterolateral extension of basiphallus (partly densely pubescent); sp, subepandrial process (on subepandrial cuticle).

Figure 36.Pentachaeta impar, Wilson River Reserve.Hypandrium and associated structures, ventral view. aa, aedeagal apodeme; ab, aedeagal bulb; as, articulating sclerite; bb, base of bulb; bp, basiphallus; df, double-funnel of bulb; dp, distiphallus; fp, fork plate (Gabelplatte) of hypandrium;g, gonostylus;pl, posterolateral extension of basiphallus (internally micropubescent); vl, ventral lobe of distiphallus.

Figures 5–10. Pentachaeta edwardsi, male; (5) surstyli in situ, posteroventral view; scale = 0.2 mm; (6) oblique posteroventral view of epandrium showing cerci; setulae omitted except on left cercus; scale = 0.2 mm; (7) left cercus, lateral view; (8) apex of right surstylus, inner view; scale = 0.04 mm; (9) anterior apex of right cercus, ventral (outer) view; scale = 0.04 mm; (10) left gonostylus and associated structures, lateral view; scale = 0.1 mm. as, articulating sclerite; g, gonostylus; il, inner lobe of gonostylus; pl, posterolateral extension of basiphallus; sp, subepandrial process (superimposed on other parts in slide preparation).