Sarabandus robustus ( LECONTE , 1875)

Zwick, Peter, 2015, To the knowledge of Sarabandus robustus (LECONTE) (Col.: Scirtidae: Scirtinae), and on the groundplan of male marsh beetle genitalia, Linzer biologische Beiträge 47 (2), pp. 1439-1449 : 1440-1444

Sarabandus robustus ( LECONTE, 1875) ( Figs 1-15 , 21 )

Cyphon robustus LECONTE, 1875 , Trans. Amer. ent. Soc. 5.

Sarabandus robustus (LECONTE) - LEECH, 1955, Pan-Pacific Entomologist 31.

Habitus ( Figs 1, 2 ): Elongate oval, relatively flat, BL 5.0-5.7mm, BL/BW ~1.85. Light brown, dorsal side irregularly punctate and finely pilose, elytra with 3 very shallow costae, no sutural stripe. Head orthognathous, in dorsal view concealed by pronotum. Base of pronotum wide, straight in front of equilateral scutellum, sinuous laterally, rear corners blunt. Sides curved, converging forward, front rounded, no trace of front corners. Disc uniformly convex. Elytra widening slightly backward from blunt humerus, body widest in caudal fourth. Epipleura narrow. Antenna longer than half BL, flagellar segments cylindrical, each several times longer than wide. Scapus unmodified, pedicle clubshaped, shorter, antennomere 3 still a bit shorter, more distal antennomeres long ( Fig. 1 ). Mandibles equal, stout with short curved sharp tip, no teeth, mola smooth and hairless ( Fig. 3 ). Maxillary palpus 4-segmented, slender, segments 2 and 3 thicker than 1 and 4 ( Fig. 4 ). Labial palpus 3-segmented, second segment widening a little distally, edge oblique, last segment long, slender, curved gently outward ( Fig. 5 ). Legs strong, unmodified. Fully winged.

Underside. Lower face of head flat, subgenal ridge unmodified, ending near insertion of maxilla, close to a branch from gular suture. Prosternal process not projecting between coxae, thin, blade-like, no setation. Mesoventral groove poorly defined, a flat roundly triangular area on front edge of mesoventrite. Mesoventral process a short pointed triangle not reaching metasternum, middle coxae partly contiguous. Discrimen visible over half of metaventrite. Abdominal sternites unmodified.

Ma l e (Figs 6-11, 21): Plate of T8 sclerotized, wider than long, caudal margin rounded, distal region with scattered setae, the largest along caudal margin without forming a regular fringe (Fig. 6). Apodemes short, not connected, caudally tapering in the plate, front end sinuous. S8 a triangular membranous structure containing a weak barely visible widely U-shaped sclerite (Fig. 7), 1 or 2 minute setae caudolaterally. T9 wider than T8, apodemes short and unconnected, plate soft, bare, caudal edge not well defined (Fig. 8). S9 (Fig. 9) is a barely sclerotized oval plate, caudally bilobed, caudal half with long setae.

Base of tegmen (Fig. 10, te) shaped like a swallowtail, strongly widening caudad and supporting two large triangular parameres (pe) whose soft blunt tips lean against the penis. There is a strong supporting rod (sr) near the medial edge of each paramere, but no spines or other armature. Styles (st) unusually large, triangular, resembling the parameres in size and shape, the blunt tip is bare. Penis strongly sclerotized, the wide front of the large oval pala shallowly excised (pa). Trigonium (Figs 10, 11, tr) a slender triangle with widely divergent basal arms (ba), dorsally with a pair of triangular outward projections near half length. The slender tip in its distal half beset with distinct teeth, mainly ventrally. Parameroids (pd) resembling elongate ears, distally with dense external denticulation, their base is of complex shape: dorsal edge of parameroid basally with large medially serrate lobe (Fig. 10, sl) extending over basal arm of trigonium. Edge of sclerite surrounding pala continues caudally as ventral edge of parameroid (Fig. 11). Transparent unarmed membranes connect parameroids and trigonium. The membrane attached to the front end of tegmen is transversely wrinkled, the outer edge appears in dorsoventral view finely serrate.

Female ( Figs 12-15 ): Abdominal sternites unmodified. Ovipositor long and slender, unmodified. Gonocoxites (gc) slender, the gonostyles (gs) are elongate slender clubs with apical sensilla. Bacula with small recurrent branchlet. The shapes of T8 and S8 are not clearly visible in the preparation. The long apodemes of T8 (aT8) converge and taper in the front edge of T8. The sclerites of S8 (aS8) delineate a slender rhomboid. Anteriorly they converge but the fine tips remain separate. Surface of the sclerites of S8 prickly, sparsely beset with microscopic spinules. Terminal section of the bacula of ovipositor similar. No vulvar sclerite but cuticle in vulva complexly folded, details not recognized. Prehensor (pr) a widened section of the gonoduct containing caudally a pair of triangular plates, each with 3 large sharp anterolateral hooks. Between the plates is a small serrate median crest. Anterolaterally the prehensor bears a pair of band-shaped lateral sclerites and a frontal sclerite arch beneath which lies the narrow anterior opening of the prehensor. At a short distance in front of the prehensor lies the balloon-like hyaline bursa (bu). The empty bursa has a diameter of 0.7mm. Its surface bears numerous circular sclerites, most 10-15µm across. Each sclerite with a central group of ~8 curved hair-like outgrowths projecting into the lumen.

I m m a t u r e S t a g e s: Unknown.

Relations of S a r a b a n d u s: In habitus Sarabandus robustus resembles several genera representing both the Microcara - and Elodes - types (in the sense of NYHOLM 1972) but it fits in none. The Elodes -clade will be discussed below. Sarabandus genitalia agree with the Microcara - type, its slender body with rounded pronotal front margin resembles, e.g., Microcara, some Pseudomicrocara, or Heterocyphon. However, the first has modified labial palpi, all three have a well developed prosternal process ending in a plate, and a complete mesoventral process separating the middle coxae.

Figs 6-11: Sarabandus robustus , male terminalia. (6) T8; (7) S8; (8) T9; (9) S9; (10) dorsal view of protracted tegmen and penis; (11) penis tip, ventral view. 6-9 and 10-11 to the same scale, respectively.

ba, basal arm of trigonium; pa, pala; pd, parameroid; pe, paramere; sl, serrate lobe; sr, supporting rod; st, stylus; te, tegmen; tr, trigonium.

Sarabandus robustus is a member of subfamily Scirtinae (in the sense of LAWRENCE & YOSHITOMI 2007). Below I discuss that its resemblances with Pseudomicrocara are in plesiomorphic traits providing no evidence of close relationships between these widely disjunct taxa, and that Sarabandus shares also no apomorphies with the Elodes -clade.

The closest relative of Sarabandus remains unknown. The number of scirtid genera in the Holarctic region is comparatively low, only four are endemic in the huge Holarctic area. Probably, this poverty reflects Pleistocene impact. I regard Sarabandus as a relict, as an isolated survivor of the Pleistocene.

Figures

Figs 1-5: Sarabandus robustus, habitus and mouthparts. (1) female, dorsal; (2) male, lateral; (3) mandible; (4) maxillar palpus; (5) labium. 1 and 2 not to scale, 3-5 to the same scale.

Figs 12-15: Sarabandus robustus, female genitalia. (12) overview, sclerites of S8 shown in black, plus an enlarged detail (arrow); (13) tip of ovipositor; (14) prehensor; (15) ornaments on surface of bursa. 12 not to scale, 13, 14 to the same scale. aS8, sclerite of S8; aT8, apodeme of T8; bu, bursa; gc, gonocoxa; gp, gonopore; gs, gonostylus; ov, baculum of ovipositor; pr, prehensor.

Figs 17-21: Suggested homologies between penes of different Scirtinae. (17) Sacodes fuscipennis, overview of tegmen and penis; (18) Sacodes fuscipennis, enlarged apex of penis in dorsal (d) and ventral (v) views; (19) Microcara testacea, penis, ventral; (20) Pseudomicrocara orientalis, caudal part of penis, ventral view, with detail of apex of parameroid in dorsal view; (21) Sarabandus robustus, partial ventral view of penis tip. Not to scale.