Chelonarium signatum, DALMAN, 1824

Shepard, William D. & Leavengood, John M., 2021, Redescription of Chelonarium signatum Dalman, 1824, with Notes on its Reproductive Biology and Occurrence in Paraguay (Coleoptera: Byrrhoidea: Chelonariidae), The Coleopterists Bulletin 75 (2), pp. 355-364 : 356-361

CHELONARIUM SIGNATUM Dalman, 1824

( Figs. 1–8 )

Redescription. Body ( Fig. 1 ) 5.9–7.2 mm long, 3.5–4.5 mm wide ( n = 48). Pronotum, scutellar shield and most of elytra light brown to brown; elytra with dark brown spots on humeri and middle of elytral margin; yellow stripe extending from suture posterior to scutellar shield, around scutellar shield then laterally to humeri and margin, encircling dark brown spots, to elytral apices and then anteriorly along suture in posterior third. Venter light brown. All appendages fit into deep grooves on venter. Head withdrawn into venter of prothorax, opisthognathous when withdrawn, prognathous when extended ( Fig. 2 ). Frons with large umbilicate punctures, most separated by own diameter or more, each umbilicate puncture with one fine short golden seta; edges flat with pronotal hypomeron and eyes; antennal ridges present; interocular area slightly convex, depressed toward frons; anterior margin tridentate in middle, middle tooth longest. Clypeus depressed under the frons, hidden from view. Labrum carinate in middle, sides depressed from level of carina; apex emarginate, disc setose. Maxilla ( Fig. 3A ) with palpus having four palpomeres, palpomeres 1–3 short, 4 long, cultriform; galea and lacinia basally fused, long, apically bifurcate and acicular. Labium ( Fig. 3B ) basally narrow and membranous; paraglossae membranous, apically acicular; labial palpus with 3 palpomeres; palpomere 1 short, 2 long, 3 long and cultriform; labial palps shorter than maxillary palps. Eyes finely faceted, facets flat on exposed surface, large and bulbous on portion hidden in repose. Antenna with 11 antennomeres; antennomere 1 very short, annular, hidden by frons when head is in repose; antennomeres 2 and 3 ( Fig. 2 ) flat, wide and heavily sclerotized, setose below; antennomere 2 quadrate; antennomere 3 twice as long as antennomere 2; antennomere 4 very short and narrow, three times longer than wide; antennomeres 5–10 subserrate; antennomere 11 fusiform; antennomeres 2 and 3 fitting into median cleft on mesoventrite. Pronotum ( Fig. 1A ) widest at posterior angles; anterior and lateral edges evenly arcuate in dorsal view, pronotal shelf not carinate dorsoventrally; disc glabrous, with shallow curved depression in anterior third that parallels anterior margin, remainder of disc convex, covered with micropunctures each having a very short, fine seta, punctures and setae more numerous in anterior third, punctures separated by own diameter in anterior third and by twice diameter or more in posterior two-thirds; posterior margin straight anterior to scutellar shield and gently curved from scutellar shield to humeri; posterior margin crenulate but hidden by overlapping elytra and scutellar shield. Scutellar shield flat; anterior margin straight, lateral margins slightly arcuate to posterior point; disc glabrous with scattered fine setae. Elytra convex, glabrous; humeri slightly protruding; a row of dark spots along suture extending from base to apex in interval 1 (spots not expressed on surface as punctures); with basal dark spots on intervals 2–5; interval 7 with four spots; interval 9 with dark spots in anterior half of elytron; base without depressions; disc with scattered micropunctures separated by more than own diameter, each micropuncture with a short, fine, decumbent seta; epipleuron when elytron in repose covered by thoracic and abdominal edges, grooved at level of abdominal ventrite 5. Metathoracic wings macropterous. Prosternum deeply excavate to receive head in repose, lateral parts of prosternum exposed, covering ventral rim of eyes; prosternal process free in groove of mesoventrite; with mesepimeron and mesanepisternum deeply cleft to receive prothoracic leg; hypomeron with disc flat and glabrous, covered with large flat-bottomed punctures, each puncture with one fine, short seta. Mesoventrite short and wide; anterior margin curved around procoxae, then slanting posteriorly; posterior margin gently arcuate medially then curved around mesocoxae; lateral margin short, dentate; disc deeply cleft medially to receive apices of antennomeres 3, anterior surface of cleft with small tooth; surface with small contiguous macropunctures having short, fine setae. Metaventrite wide, trapezoidal, convex, widest posteriorly; anterior margin arcuate and rimmed between mesocoxae; lateral margin gently arcuate; posterior margin straight except slightly protruding medially; disc smooth, glabrous, covered with scattered micropunctures separated by more than own diameter, each micropuncture with a short, fine seta, with discrimen (not expressed as suture on surface) and short black transverse lines just anterior to posterior margin; metanepisternum elongate, anterior part excavate to receive mesothoracic leg. Legs with flattened coxae, femora and tibiae fitting tightly into grooves ( Fig. 1C ); all surfaces with micropunctures and fine setae, pro- and mesotrochanters with posterior fringe of golden setae; pro- and mesocoxae more or less conical, procoxa dentate apically; metacoxa short, very transverse, laterally reaching epipleuron, with posteriorly directed fringe of golden setae, all coxae with small umbilicate punctures; protrochanter cleft apically to receive part of prosternum. Femora longitudinally grooved to receive tibiae. Tibiae narrow, as long as femur + trochanter, lateral margins sharp; protibia with lateral margin dentate; meso- and metatibiae apically with rows of long golden setae. Tarsi each with five tarsomeres; tarsomeres 1 and 2 twice as long as wide, ventrally with a brush of numerous long, golden setae; tarsomere 3 half as long as tarsomere 2, with long fleshy lobe underlying tarsomeres 4 and 5; tarsomere 4 similar to tarsomere 3 but not lobed; tarsomere 5 as long as tarsomeres 1–4 combined; claw with long rectangular basal tooth; protarsus covered by protibia when leg retracted. Abdomen ( Fig. 1C ) with five ventrites, convex, glabrous, surface covered with scattered micropunctures and short setae; anterior part of ventrite 1 deeply excavate to receive metathoracic leg, anterior border and excavation rimmed; ventrite 5 evenly curved posteriorly, punctures and setae denser in apical half. Aedeagus ( Figs. 4–5 ) approximately 1.8 mm long; basal piece 1.0 mm long, rounded basally, parallel-sided, open in basal half dorsally, closed ventrally and in apical half dorsally; parameres ( Figs. 4–5 ) 0.25 mm long, heavily sclerotized in middle, membranous and heavily setose apically, dorsally bilobed at apex of sclerotized area; median piece 1.0 mm long, with two basal apophyses, apically heavily sclerotized, broadly lanceolate apically; accessory sclerite (= median process of Sharp and Muir 1912) ventral to median piece, 1.6 mm long, Y-shaped basally, then long and filamentous to sharp tip, tip extending beyond parameres and curved forming a hook with apex curved to right side. Ovipositor ( Figs. 6–7 ) 3.0 mm long; bacula 2.7 mm long, coxites 0.3 mm long; bacula ( Figs. 6A, C ) anteriorly flared, lightly sclerotized, median edge well sclerotized, apically articulated to middle of coxite base; ventrally with long narrow accessory sclerite medially between bacula and attached to coxites; coxites well sclerotized ( Fig. 7 ), elongately triangular, bases with notch for articulation on the bacula apices, apices acute, dorsally with narrow acicular anteriorly-directed spur; styli absent.

Variation. Body measurements overlap except that some females are larger than all males. Males are 5.9–6.6 mm long and 3.5–4.1 mm wide ( n = 29) while females are 6.2–7.2 mm long and 3.6–4.5 mm wide ( n = 19).

Diagnosis. The yellow stripe curving across the top and down the side of each elytron ( Fig. 1 ) is unique among all other species in Paraguay. The pronotum has the apical and lateral margins evenly curved and the pronotal shelf is not carinate.

Lectotype Designation. The original description does not indicate how many specimens were examined. The single specimen in the NHRS has been traced from its collection in Brazil to its current deposition in the NHRS. The red “Typus” label on the specimen ( Fig. 9 ) was not placed on the specimen by Dalman ( J. Bergsten, in litt.). Therefore, pursuant to ICZN Recommendation 73F ( ICZN 1999), the NHRS specimen is designated the lectotype for Chelonarium signatum Dalman, 1824 .

Specimens Examined. Lectotype: BRAZILIA, NHRS-JLKB00071806 (1A, NHRS). PARAGUAY: Guairá Dept.: / Hotel Independencia , vic. / Independencia, 10-20-XII-2019 / JE Eger & JM Leavengood, 617 ft / S 25°43.069′ W 56°16.443′ ( 6M, 4F, JMLC); PARAGUAY: Guairá / Dept.: ca. Salto Suizo / 1.6 km NE of Rancho / Don Juan 13- XII-2019 / Coll. JM Leavengood ( 1M, 1F, EMEC); PARAGUAY: Itapua Dept.: / vic. Pro Cosara Nature Reserve / S 26°38.271′ W 055°39.850′ / Elev. 933 ft., 9-10-XII-2019 / Coll: JE Eger, W Tyson, JB / Heppner & JM Leavengood ( 5M, 3F, JMLC); PARAGUAY: Misiones Dept / San Ignacio, Hotel Rural / S 26°52.508′ W 56°59.355′ / 451 ft, BL & MV lights / Coll JE Eger, W Tyson & / JM Leavengood 5-8 XII 2019 ( 3M, 5F, EMEC); PARAGUAY: Paraguari Dept.: / vic. Hotel Gabriela , nr. Paraguari , / S 25°35.630′ W 057°07.495′ / Elevation 504 ft., MV + BL / Colls: W Tyson, JE Eger & JM / Leavengood 1-4-XII-2019 ( 11M, 2F, JMLC; 4M, 4F, IBNP); PARAGUAY / Ňuadu’a, Paraguari / Nov.19, 1987 / Joan Kandel (1A, EMEC).

Etymology. Dalman did not indicate an etymology. However, signatum is a Latin participle meaning impressed, designated or noted. Perhaps this refers to the distinctive yellow elytral color pattern.

Remarks. Photographs of the lectotype of C. signatum ( Fig. 8 ) were provided by the NHRS. The specimen is slightly damaged from being pinned. These photographs were compared with the original description and our specimens to verify our species identifications. NHRS confirms they only have a single specimen so it is likely this was the only specimen used for the original description. Both the original description ( Dalman 1824) and the original labels ( Fig. 8C ) list Freyreiss as the collector. The genitalia of the lectotype have not been dissected (J. Bergsten, in litt.).

The Kandel specimen (EMEC) has four mites attached to the posterior of the left elytron. This appears to be a case of phoresy.

Antennomeres 4–11 are free from the ventral body surface and are thus subject to abrasion; on many specimens they are missing.

Reproductive Biology. Ten of the 19 females dissected had eggs: three females had one egg, three had two eggs, one had three eggs, one had four eggs, one had 10 eggs and one had 12 eggs. The largest females were not the ones with the larger number of eggs.All females with eggs were collected during December so this month is within the reproductive period. The oblong and cylindrical eggs ( n = 2) were 0.5 mm long and 0.3 mm wide, with a micropyle on one end. The micropyle is on a small raised cylinder. The overall sex ratio of our specimens is 1.58:1 ( n = 49, 30M, 19F).

Collection and Habitat. In Paraguay our collections are from the southern departments ( Guairá, Itapúa, Misiones and Paragaurí). Most specimens were collected at lights while some are from beating vegetation. Specimens were collected at elevations of 451–933 ft ( 138–283 m). A typical habitat where we collected C. signatum is shown in Fig. 9 . This area is a forest corridor in ranch land, with secondary growth. The location is probably in the Pastizales Ecological Region , but on the border with Humid Chaco.

Figures

Figs. 1–3. Chelonarium signatum. 1) Habitus: A) Dorsal, B) Lateral, C) Ventral. 2) Head, extended; 3) Head: A) Right ventrolateral view, B) Ventral view.

Figs. 4–5. Chelonarium signatum. 4) Aedeagus: A) Dorsal, B) Lateral, C) Ventral. 5) Paramere apices showing setation.

Figs. 6–7. Chelonarium signatum. 6) Ovipositor: A) Dorsal, B) Lateral, C) Ventral. 7) Tip of ovipositor: A) Dorsal, showing anteriorly-directed spurs on the coxites, B) Ventral, showing attachment of accessory sclerite to coxites.

Fig. 8. Chelonarium signatum, lectotype. A) Dorsal, B) Ventral, C) Labels. Photographs by Johannes Bergsten (©2020 Naturhistoriska riksmuseet). Original photos cropped, light levels and contrast adjusted. Made available by the Swedish Museum of Natural History under Creative Commons Attribution 4.0 International Public License, CC-BY 4.0.

Fig. 9. Chelonarium signatum, habitat at Misiones, Paraguay.