Phormiobius Broun, 1917

Shen, Jia-Wei, Choi, Su-Ho & Leschen, Richard A. B., 2020, Revision of the New Zealand endemic genus Phormiobius (Coleoptera: Staphylinidae: Pselaphinae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 60 (2), pp. 553-564 : 554-556

Phormiobius Broun, 1917

( Figs 1–2 )

Phormiobius Broun, 1917: 381 . Type species: Phormiobius halli Broun, 1917: 382 , by monotypy.

Redescription. Body length 2.14–2.77 mm, elongate in dorsal view; vestiture of long decumbent curved or straight setae; surfaces glabrous, micropunctate, and lacking distinct microsculpture; body colour dark reddish-brown to dark-brown, mouthparts, and tarsi paler. Head ( Figs 1A–C ) elongate, about 2× longer than wide, with frons bilobate and moderately projecting, forming short abroad rostrum; weak vertexal sulcus demarking posterior margins of rostrum, lacking frontal fovea; vertex bifoveate, asetose fovea ( Fig. 1A ) small; subantennal excavations broad and separated by narrow median carina and bounded by distinct epistomal ridge ( Fig. 1B ), genal carina absent, dorsal postantennal pits present and small, tempora weakly rounded; eyes small and coarsely facetted [13–19 facets]. Antenna ( Fig. 2E ) with 11 antennomeres, antennal club formed by three terminal antennomeres, finely tuberculate and pubescent, lacking distinct apical or subapical rims, antennomere 1 (scape) about twice as long as wide, pedicel about 1.2× longer than wide, A3–A8 with ratio of length/ width subequal, A9 moderately transverse, about 1.2× wider than long, A10 transverse, about 1.4× wider than long, A11 elongate and symmetrical, about 1.8× longer than wide. Maxillary palpi ( Fig. 1G ) with P2 pedunculate at base, about twice the length of P3, P4 with sensory area bearing single elongate apical sensillum; posterior gular region slightly convex, with large, single posterior tentorial pits ( Fig. 1C ).

Prothorax ( Fig. 1E ) slightly wider than long, and spindle-shaped and widest at apical two-fifths, setose lateral procoxal foveae medium-sized; pronotum ( Fig. 1D ) lacking antebasal sulcus, setose lateral antebasal fovea large, median antebasal fovea setose and well-developed.

Elytra ( Fig. 1F ) shorter than abdomen, combined width about 2× wider than long, with distinctively constricted bases, forming lip-like basal rim, posterior edge sinuate; each elytron with two asetose subbasal foveae and two asetose basal fovea; lacking discal striae.

Mesoventrite ( Fig. 2C ) with shallow asetose prepectal foveae, well-developed setose median mesoventral fovea flanked by well-developed setose lateral mesoventral foveae with branches that do not join at middle, with small asetose anterolateral mesoventral foveae. Mesoventrite and metaventrite fused. Lateral mesocoxal foveae setose and deep, lacking median and lateral metaventral fovea, metaventral notch narrow and short.

Abdomen ( Figs 2A–B ) moderately convex, dorsoventrally not strongly flattened; tergites moderately convex, with well-developed transverse basal grooves or sulci lined with ctenidia, lacking discal carinae; T1 slightly shorter than T2, T3 elongate and subequal to combined lengths of T1 + T2, T4 subequal to T2; asetose basolateral fovea present on T1–T4, T1–T3 trifoveate on each side, T4 unifoveate; T5 of male broadly rounded or truncate. Paratergites well developed. Abdominal ventrites 1–4 bifoveate, with large and open pocket-shape asetose basolateral foveae, V4 with vaguely visible fovea on the inner side of each basolateral fovea; males with narrow to broad concavities or impressions on V2 and V3, and sometimes V1 and V4. Abdominal ventrite 5 of male with apex emarginated, abdominal V5 of female with apex entire. Male V6 (penial plate) sclerotized and easily visible in ventral view. Legs long and slender, metatrochanter of male with modified processes, male metafemora ( Fig. 2D ) weakly to strongly elbowed, tibia more or less parallel-sided and not strongly curved, metatibia of male nearly straight or weakly bent at apical one-fourth, small apical spine present. Aedeagus symmetrical, lacking parameres, basal capsule sub-globo- se; internal sac with large sclerites (lacking in P. graceae sp. nov.); median lobe uni- to multi-lobate.

Differential diagnosis. Phormiobius can easily be distinguished by having pyramidal elytra that are short, transverse and narrowed basally and lacking grooves or carinae, a broad abdomen (not dorsoventrally flattened) with T1 and T2 subequal in length, and T3 the longest; males have distinct concavities on abdominal ventrites, and lack well-developed sulci on head and pronotum. Other characters that differentiate this genus from other tyrines are head with a well-developed bilobate frons (rostrum), antennal lobes contiguous and divided by narrow sulcus, vertex bifoveate, lacking frontal fovea and genal carina, maxillary palpi with P2 pedunculate at base and P4 fusiform to oval, not pedunculate; and pronotum with well-developed antebasal fovea, lacking antebasal sulcus.

Comments to classification. The phylogenetic relationship of Phormiobius to other tyrines is uncertain and a worldwide revision and comprehensive phylogenetic study is needed. In the generic key of the subtribe Tyrina by Hඅൺඏගč & CΗൺඇൽඅൾ*© (2005), Phormiobius is keyed out to a couplet that includes southern South American and Australian taxa but shares some characteristics with some taxa outside this region. For example, the pyramidal shaped elytra with strongly narrowed bases are distinctive for other tyrines (see Hඅൺඏගč & CΗൺඇൽඅൾ*© 2005; Agatyrus ( New Zealand), Anagonus Fauvel, 1903 ( New Caledonia), Franziotus Leleup, 1972 ( Madagascar) , Mipseltyrus Park, 1953 (North America), Plesiotyrus ( New Zealand), Tyrinasius Kurbatov, 1993 (Asia) and Tyrogetus (Australasia) , and Zeatyrus ( New Zealand)), and among them the length of T1 and T2 are unequal in Mipseltyrus, Tyranasius , and Tyrogetus . Among the world fauna, Phormiobius is most like Franziotus , by greatly reduced elytra that are distinctly narrower than abdomen. The elytral and abdominal characters are variable and used for generic diagnostics for tyrines, and the pyramidal elytra could be associated with hind wing loss or reduction as the case of Phormiobius .

With respect to the New Zealand fauna, B*©ඈඎඇ (1917) suggested that Phormiobius was closest to Tyrogetus , but among the currently described genera, it is actually most like Agatyrus differing from it by the absence of elytral grooves and small vertexal fovea on head. Zeatyrus also lacks elytral grooves or carinae and it lacks pronotal foveature. However, Zeatyrus is unusual among the New Zealand tyrines by having an inflated maxillary palpomere 4 and also has a relatively small triangular palpomere 3 that is about as wide as long, a diagnostic character of Somatipoinina (CΗൺඇൽඅൾ*© 2001). Contrary to other Somatipoinina, the mesal sulcus of the enlarged palpomere 4 does not form a distinct furrow in Zeatyrus , rather it is broad with a large concave surface, which may be a derived form within Tyrini and other Somatipoinina.

Zeatyrus lacks a metaventral notch into which the abdominal process of abdominal ventrite fits into, a character that is variable in Tyrina and present also in Phormiobius .

With respect to new genera and species to be described in

a later paper, Phormiobius resembles two species which have a reduced basal elytral foveal pattern, and the male has a distinctive clypeal horn.

Sexual dimorphism in pselaphines is rampant (e.g., CΗൺඇൽඅൾ*© 2001) and apart from their distinctive body form, a defining feature of Phormiobius species is the distinctive concavities present on the male abdominal ventrites. These may be deep, asetose and polished, with a distinct edge, or shallow, or setose with a pair of posterior spines and with an ill-defined edge. Function of these concavities, as well as the presence of modified metatrochanteral processes of the males, requires observation of live specimens.

Biology. Specimens were collected by sifting leaf litter and moss, but we are unsure if they are specific to certain microhabitats, like moss, which is a poorly studied habitat for New Zealand pselaphines in general (SΗൾඇ et al. 2020). Two species are known by singletons, P. brouni sp. nov., from Nelson, and P. ramsayi sp. nov., from Waikato, and therefore, special efforts should be made to collect these species to determine their threatened species status (see LൾඌർΗൾඇ et al. 2012) and their habitat preferences.

Figures

Fig. 1. Morphology of Phormiobius Broun, 1917 (based on P. graceae sp. nov.).A – head, in dorsal view; B – same, in lateral view; C – same, in ventral view; D – pronotum; E – prothorax; F – elytra, in dorsal view; G – mouth parts.Abbreviations: bef – basal elytral foveae, er – epistomal ridge, gf – gular foveae, laf – lateral antebasal foveae, lpcf – lateral procoxal foveae, maf – median antebasal fovea, sef – subbasal elytral foveae, vf – vertexal foveae. Scale bars = 0.2 mm.

Fig. 2. Morphology of Phormiobius Broun. A – T4–T8; B – V4–V7; C – meso- and metaventrite; D – metafemora; E – antenna.Abbreviations: almsf – anterolateral mesoventral foveae, blf – basolateral foveae, lmcf – lateral mesocoxal foveae, lmvf – lateral mesoventral foveae, mmsf – median mesoventral foveae, ppf – prepectal foveae. Scale bars = 0.2 mm.