Jubogaster towai, Parker & Maruyama, 2013

Parker, Joseph & Maruyama, Munetoshi, 2013, Jubogaster towai, a new Neotropical genus and species of Trogastrini (Coleoptera: Staphylinidae: Pselaphinae) exhibiting myrmecophily and extreme body enlargement, Zootaxa 3630 (2), pp. 369-378 : 372-375

Jubogaster towai sp. nov.

type material. Holotype, male, Peru, Satipo, Santa Ana , 25 I 2012, with Pheidole xanthogaster Wilson. Specimen deposited in Field Museum of Natural History, Chicago, IL, USA, with catalog number: FMNH-INS 0000 093 389 .

Diagnosis. The sole known species of Jubogaster is highly distinctive among Trogastrini due to its greatly enlarged and robust body covered in thick, blunt golden setae, the unique concave head that lacks vertexal fovea, the large, circular excavations on the frons that receive the long, geniculate antennae, the absence of a genal beard, an afoveate pronotum and elytra, the two equally-sized tarsal claws, and the bifid anterior protarsal claw.

Etymology. The new species is named in honour of Towa Shimada, son of Taku Shimada, a remarkable collector of myrmecophiles.

Description. Body length 5.1mm ( Fig 1 ). Colour dark reddish brown, antennae and legs somewhat lighter. Integument shiny. Most dorsal regions covered by conspicuous thick, erect, blunt golden setae, arranged at regularly spaced intervals and orientated posteriorly (depicted most clearly in figures 4 – 6). These are interspersed with shorter pubescence of the same colour, also orientated posteriorly. Ventral surfaces covered with fine, mostly aciculate golden pubescence ( Fig 2 ).

Head: Eyes moderate in size. Transverse, triangular head ( Fig 4 ) widest just behind eyes. Vertex and occiput uniformly setiferous with thick, blunt, erect golden setae, and shorter, sharper pubescence. Margins of large lateral cavities for antennal insertion and maxillary palp retraction carinate; interiors of cavities glabrous ( Fig 5 ). Neck approximately 0.4x head width between eyes, shining and with sparse, very short dark setae on dorsal side; glabrous and with finger-print-like (“strigate”) microsculpturation on ventral side. Fourth segments of maxillary palpi ( Fig 5 ) densely covered in short golden setae. Antennae ( Fig 3 ) pigmented similarly to tibia and very elongate, approximately 2x pronotum length. Antennomere I conical, widest in basal half and equal in length to III+IV combined. Laterodorsal margin with short arcuate carina extending to one-quarter antennomere length. Lateral face glabrous in basal half. With circular apical notch to permit geniculation with II; II small and cylindrical, approximately 0.6x the length of III; III cylindrical-obconical, equal in length to IV; IV cylindrical, twice as long as wide; V slightly shorter and narrower than IV; V – VIII cylindrical-obconical, becoming gradually shorter apically, so that segment V is almost 2x longer than wide and VIII is as only slightly longer than wide; IX – X much larger, IX almost as long as VI – VIII combined; X slightly longer than VII+VIII combined. Both IX and X cylindrical-obconical, apical margins somewhat sloping interiorly due to slight lengthening of exterior antennomere face relative to interior face. Antennomere XI longest, twice the length of X; exterior face shallowly and evenly convex, interior face weakly concave before bending obtusely to form conical apex. Several long sensory setae on apical third ( Fig 3 ).

Thorax: Pronotum ( Fig 4 ) obcordate, margins smooth, lacking crenulations or other protuberances. Uniformly setiferous and pubescent. Prosternum with lateral longitudinal carinae abruptly bending dorsally on reaching base ( Fig 2 ). Region between carinae with reduced setation and pubescence relative to lateral regions, and with small transverse projection situated medially, anterior to procoxae. Region between carinae projecting sharply in basolateral portions to receive procoxae. Mesosternum with setiferous median mesosternal foveae (MMSF) and lateral mesocoxal fovea (LMCF). Region anterior to mesocoxae formed into a shield-shaped plate with carinate margins. Anterior margin of metasternum carinate around mesocoxae. Convex metasternum with median declivity adjacent to metacoxal projections. Metasternum uniformly covered with yellow pubescence of intermediate length. Median declivity somewhat less pubescent. Lateral metasternal fovea small and setiferous. Posterior margin of metasternum bow shaped ( Fig 2 ); projection between metacoxae with small medial indentation.

Abdomen: Tergites strongly convex with visible tergite 1 (IV) sloping to abdomen base. Visible tergite 2 (V) broadest, slightly broader than 1 (IV), with segments 3 – 5 (VI – VIII) evenly narrowing. Tergite 4 (VII) longest, approximately 1.5x tergite 3 (VI). Broad paratergites on segments 1 – 3 (IV – VI); paratergite margins of segment 4 converging apically to create a triangular paratergite. Anterior edges of abdominal tergites with narrow band of black pigment. Remainder of tergite reddish brown; intertergital membrane yellow with latticed microsculpture. Base of visible tergite 1 (IV) with short, blunt tubercles, situated halfway between midline and lateral margin. First visible sternite (IV) medially acuminate in anterior half, projecting ventrally between metacoxae. Last visible segment (6; VIII) with median declivity. Sternite 7 (XI) internalised. Pubescence on sternites 2 – 6 (IV – VIII) becoming finer and sparser toward midline ( Fig 2 ).

Elytra: Blunt setae on elytra somewhat longer and slightly thicker than on other parts of body. Apicolateral angles of elytra with margins weakly excised ( Fig 6 ).

Legs: Coxae contiguous. Mesocoxae with proximodistal carina along posterior face. Metacoxae glabrous except for pubescence on internal face and around projection to trochanter. Apices of metacoxae produced into flat, blunt spines that extend posteriorly to half trochanter length ( Fig 7 ). Metatrochanters with small rhomboid-shaped tubercles on exterior face ( Fig 7 ). Femora brownish red, covered with thick, blunt golden setae. Tibia somewhat flattened in proximal half, carinate along anterior edge to half-tibia length. Tibia lighter in colour than femora, yellowish brown, with similar but shorter setae. Tarsi narrow and longer than half tibial length; also yellowish brown, with fine, sharp, aciculate setae. Protarsus with bifid anterior claw ( Fig 8 ).

Aedeagus: Asymmetric, broad, lacking parameres ( Fig 9 and 10 ). Wide, globose basal bulb with asymmetric left and right apical projections. An asymmetric, apically-truncate sclerotised stylus emerges from within the basal bulb.

Biological and collection information. The single specimen of J. towai was collected in a colony of Pheidole xanthogaster Wilson under a log. The ants were apparently unaware of the beetle, which was was found deep inside the nest. This suggests that J. towai is a true myrmecophile, but information about its biology and behaviour are unavailable at this time. It has no clear myrmecophilous adaptions, so may belong to the “obligate synoekete” class.

Comments. J. towai has distinctly internalised terminal tergites and sternites. The plesiomorphic condition in Pselaphinae is for visible sternite 7 (IX) to form a penial plate, flanked by left and right sclerites formed from visible tergite 6 (which is also segment IX). However, in J. towai , segment IX is internalized; in figure 2 the internal sclerites can be seen enclosed within the genital aperture. This arrangement makes segment VIII (visible sternite 6 and visible tergite 5) the posterior-most external segment. Don Chandler (University of New Hampshire) has kindly surveyed the character state of segment 7 (XI) and found internalisation to be relatively common in Trogastrini : in many genera the segment is not externally visibile ( Rhexinia Raffray , Xerhius Raffray , Aporhexius Raffray , Rhexius LeConte , Eurhexius Sharp , Platomesus Chandler , Austrorhexius Chandler ) while in others it is clearly present ( Conoplectus Brendel, Fletcherhexius Park , Adrogaster Raffray ). In still others, the segment is visible but thin ( Anarmodius Raffray , Rhexidius Casey ). Two genera, Oropus and Mesoplatus , are polymorphic, with species falling into two or all of the three classes. Furthermore, in most Jubini and some Goniaceritae, segment 7 is not externally apparent (D. S. Chandler, pers comm.). Hence, a recurring trend is for internalization of the terminal segment, as exemplified by J. towai .

Figures

FIGURES 1 – 7. Jubogaster towai Parker and Maruyama. 1) dorsal habitus 2) ventral habitus 3) left antenna, exterior face is to the left 4) vertex of head and pronotum 5) frontal of view of head, showing excavations for antennae and maxillary palpi 6) right elytron apical angle showing excision 7) left metacoxa, metatrochanter with arrow pointing to rhomboid-shaped tubercle.

FIGURES 8 – 10. 8) apical protarsus showing bifid anterior protarsal claw 9) aedeagus, ventral view 10) aedeagus, dorsal view.