Parygrus Erichson, 1847

Barr, Cheryl B. & Shepard, William D., 2020, Hiding in plain sight: rediscovery and review of Parygrus Erichson, 1847, with description of five new species from the Neotropics (Coleoptera: Byrrhoidea Dryopidae), Zootaxa 4755 (1), pp. 99-128 : 101-104

Genus Parygrus Erichson, 1847

Type species. Parygrus erichsoni Waterhouse, 1876 ; designated by subsequent monotypy.

Diagnosis. Parygrus shares antennal morphology with Helichus , but the two genera can be separated by the following characters: Parygrus is very pubescent, covered with erect and semi-erect setae, including the eyes; plastron setae are not present; the enlarged 2nd antennomere covers antennomeres 3–4 or 3–5. Helichus is covered with recumbent plastron setae and lacks erect setae, the eyes are bare; the enlarged 2nd antennomere covers all of the distal antennomeres. Because of its pubescence, Parygrus appears most similar to Pelonomus , Microparnus , Onopelmus Spangler , Dryops Olivier and Platyparnus . These genera differ from Parygrus by the following: Pelonomus does not have an enlarged 2nd antennomere; Microparnus has 10 antennomeres and Onopelmus has 13; Dryops and Platyparnus have pronotal sublateral carinae/sulci.

Generic redescription. Size from 4–8 mm long; elongate, parallel-sided or somewhat wider at posterior 1/3, moderately convex in lateral view; color uniformly brown; very setose, covered with long, stout, erect and/or semierect setae and shorter, finer, recumbent setae.

Head covered with erect setae; frons projecting slightly or prominently forward between antennal bases; vertex flattened or shallowly depressed between eyes. Eyes hemispherical, protuberant, covered with erect setae, finely faceted. Antennae densely setose, pectinate, with 11 antennomeres; antennomere 2 enlarged, trapezoid, covering antennomeres 3–5 or 3–6; antennomere 3 shortest; antennomeres 4–11 forming a loose club; subantennal grooves deep below eyes; insertions approximate. Clypeus sub-triangular, wider than long. Labrum transverse, shorter than clypeus. Mandible with four teeth; ventral two teeth larger, acutely pointed; dorsal two teeth smaller, blunt, closely appressed. Maxillary palpi each with four palpomeres; labial palpi each with three palpomeres.

Pronotum wider (~1.25x) than long; narrowly marginate and sometimes explanate laterally; anterior angles very acute; posterior angles barely acute, depressed; carinae absent, disc slightly flattened; punctate with large, distinct punctures interspersed with very small, fine punctures. Hypomeron flat, wide, narrower near anterior margin. Scutellum : shape variable, anterior margin arcuate.

Elytron without carinae; finely or coarsely punctate-striate, with nine rows of punctures; narrowly margined. Epipleuron sinuate, broad in basal 1/3, narrow in apical 2/3 with groove to receive lateral edge of abdominal ventrite 5. Hind wing: macropterous (in species examined).

Legs with major structures similarly proportioned; proleg shortest, metaleg longest. Procoxae oblong and flat, more widely separated than meso- and metacoxae; mesocoxae globular, separated by about one coxal width; metacoxae transverse, separated by about same distance as mesocoxae, excavate to receive femora; metatrochanters swollen; protibia weakly to strongly arcuate, sometimes deflexed (males); mesotibia weakly to moderately arcuate; metatibia straight; tarsomeres increasingly longer from base to apex, tarsomeres 1 and 2 very short, tarsomere 5 as long as previous 4 combined; claws simple.

Venter with short, fine, recumbent setae present on lateral surfaces including hypomera, pro-, meso- and metepisterna, mesepimera, epipleura; long, semi-recumbent setae present medially. Prosternum long; lateral surface angled at about 45° to central disc; prosternal process broad between procoxae, laterally margined, with a median, longitudinal carina terminating in a low protuberance. Mesoventrite very short, deeply excavate to receive prosternal spine. Metaventrite long, projecting anteriorly between mesocoxae, margined; lateral surface angled at about 45° to posterior disc; metathoracic discrimen distinct; posterior border bidentate between metacoxae; metanepisternum wider anteriorly than posteriorly. Abdomen convex, with 5 ventrites; punctures aligned with faint, transverse strigae; ventrite 1 with margined, triangular intercoxal process, posterior border straight; ventrites 2–4 transverse, subequal in length; ventrite 5 longer, with broadly rounded apex.

Genitalia. Male genitalia, trilobate type; female genitalia, common type ( Kodada et al. 2016).

Original description. Erichson’s 1847 descriptions of Parygrus and Helichus were presented in an annotated key. He cited the following characters for separating genera with “auriculate” antennae: Middle legs close to each other ( Parygrus and Parnus ); middle legs further apart ( Helichus and Dryops ). In addition, he stated that in Parygrus the elytra are clearly punctate-striate, and the antenna clearly “11-membered.” Waterhouse (1876), in his paper describing the type species P. erichsoni , stated that Erichson had established the genus to include undescribed species from South America with narrow form and strongly striated elytra.

Sexual variation and dimorphism. Females are generally larger than males, and have a small, angular protuberance at the middle apex of abdominal ventrite 5 which is formed by a ventrally-directed fold. This feature is absent in males and therefore very useful in externally determining the sex of individuals. In the specimens we have examined, the protibiae of females were not deflexed and were usually less arcuate than those of conspecific males.

Reproductive period. Fifteen females were collected along with 11 males from Paraguay, Alto Paraguay, Puerto Esperanza, 2 nd December 2006. Dissection found eggs in 13 of the 15 females. Thus the austral summer is the reproductive period. This is also true for Pelonomus spp. from Paraguay (W.D. Shepard, unpublished data).

Geographic distribution. Parygrus is recorded from Mexico, south through Central America and the South American countries of Venezuela, Colombia, Ecuador, Peru, Bolivia, Paraguay, Brazil, and Argentina (Figs 2, 3, 4).

Key to the genera of Neotropical aquatic and semiaquatic Dryopidae

1 Body dorsally glabrous; lateral margin of each elytron interrupted near apex by a densely pubescent depression................................................................................................ Elmoparnus Sharp

– Body dorsally pubescent or with plastron; lateral margin of each elytron without densely pubescent depression.......... 2

2 Pronotum with complete sublateral carina/sulcus on each side....................................... Dryops Olivier

– Pronotum without sublateral carinae/sulci or with only short carinae/sulci........................................ 3

3 Pronotum with sublateral carinae/sulci only in basal 1/4 to 1/3 .................................................. 8

– Pronotum without sublateral carinae/sulci.................................................................. 4

4 Each antenna with 13 antennomeres...................................................... Onopelmus Spangler

– Each antenna with 9 or 11 antennomeres.................................................................. 5

5 Each antenna with 9 antennomeres........................................................ Guaranius Spangler

– Each antenna with 11 antennomeres.................................................................... ... 6

6 Antennomere 2 enlarged and covering rest of antennomeres..................................... Helichus Erichson

– Antennomere 2 may be enlarged but not covering rest of antennomeres.......................................... 7

7 Antennomere 2 enlarged and at least covering antennomeres 3 and 4................................ Parygrus Erichson

– Antennomere 2 not enlarged............................................................. Pelonomus Erichson

8 Length 6–10 mm; each antenna with 11 antennomeres; pro- and mesotarsus with tarsomere 2 wide and flattened in males............................................................................... Platyparnus Shepard and Barr

– Length 2–3 mm; each antenna with 10 antennomeres; no tarsomeres wide and flattened........... .. Microparnus Shepard