Mychocerinus depressus (LeConte)

Jałoszyński, Paweł & Ślipiński, Adam, 2022, Revision of the family Murmidiidae (Coleoptera: Coccinelloidea), Zootaxa 5109 (1), pp. 1-102 : 92-94

Mychocerinus depressus (LeConte)

( Figs 286–292 )

Murmidius depressus LeConte, 1866: 376 .

Mychocerus depressus: LeConte, 1869 ; Lawrence & Stephan, 1975: 145.

Mychocerinus depressus: Slipinski, 1990: 85 .

Type material examined. Holotype ( USA): sex unknown, “D.C.”, “ M. depressus / Lec.”, “Mychocerus / depressus / (Lec)”, “Type / 6829” ( MCZ).

Additional material studied. USA: 1 ex., Illinois, Champ. Co., Mahomet, Nettie Hart Forest Mem., 25- 26.07.1966, black light trap, M.W. Sanderson leg. ( FMNH) ; 1 ex., Florida, Dunedin, W.S. Blatchley Coll. ( BMNH) ; 2 exx, Arkansas, SW of Fayetteville , dead oak berlesate, 05.10.1987, R. Leschen leg. ( USNM) ; 1 ex., Virginia, King Geo. Co., Mathias Point , 14.04.1985, W.E. Steiner, J.M. Hill, J.E. Lowry leg. ( USNM) ; 1 ex., Virginia, Caroline Co, 5 km N Hillsboro, Tuckahoe State Park , 07.01.1984, W.E. Steiner, J. Boyd, J.E. Lowry, A. Gerberich leg. ( USNM) ; 2 exx, Maryland, Montg Co., 2 km N Sunshine, at Patuxent River , 21.12.1986, W.E. Steiner, J.M. Swearingen leg. ( USNM) ; 1 ex., Maryland, Pr. Geo. Co., Landover , 38º56’N, 76º54’W, 31.01.1993, under bark of dead stand- ing Quercus coccinea, W.E. Stiner, J.M. Swearingen leg. ( USNM) ; 1 ex., Maryland, Anne Arundel Co., Bristol , 07.11.1970, under bark, M. Druckenbrod ( USNM) ; 2 exx (incl. disarticulated ♂), Maryland, Prince Geo. Co., Col- lege Park, 03.1972, W.E. Steiner ( USNM) ; 1 ex., Texas, Conroe , 02.1971, K. Stephan leg. (cPJ) .

Emended diagnosis. Body elongate oval, uniformly light brown; dorsal pubescence recumbent and relatively dense; pronotum strongly narrowing from base; two irregular groups of moderately large punctures are present on sides of pronotal disc, but regions along lateral carinae bear only few such punctures, median region virtually impunctate; elytral punctures fine on anteromedian adsutural region but distinct and moderately dense on sides, in longitudinal rows separated by spaces 1‒2 × their diameters; posterior regions of lateral longitudinal carinae of mesoventral plate forming an angle of ~20 degree with longitudinal body axis; parameres stout, ~1.5 times as long as broad, with setae distributed from near base.

Redescription. BL 0.90–1.08 mm; BL/EW 1.45–1.60. Body moderately elongate oval ( Figs 286–288 ) and in lateral view weakly convex ( Fig. 289 ), with highest site situated near middle of elytra; pigmentation light brown; dorsum covered with short yellowish recumbent and relatively short setae; clypeus with very fine but distinct microreticulation, semi-matt, reticulation on remaining body parts present but superficial and very fine, indistinct.

Head 0.25–0.30 mm wide; frons and vertex weakly convex, distinct punctures distributed mainly on sides of vertex, in some specimens also on median region of vertex, shallow, separated by spaces subequal to their diameters; clypeus semi-matt; eyes large, strongly convex, coarsely faceted.

Pronotum ( Figs 286‒287 ) strongly transverse, broadest at base; PL 0.20–0.24 mm, PW 0.46–0.55 mm, PL/PW 0.41–0.45; lateral margins weakly rounded in posterior half and more strongly so in anterior half, where they are strongly converging anterad; lateral carinae narrow but distinct; anterior pronotal margin lacking marginal line. In most specimens a pair of large, very shallow, diffuse and oval submedian impressions is present in posterior half of disc, often difficult to see and indistinct. Punctures on disc uneven, in most specimens moderately large, distinct punctures are distributed mainly in two submedian groups separated by median virtually impunctate area, and laterally not reaching lateral margins, only a few distinct punctures are distributed along lateral carinae; punctures on sites where they are most distinct are separated by spaces as wide as 1‒3 their diameters.

Prosternum ( Fig. 288 ) with distinct microreticulation and with fine, inconspicuous setiferous punctures; prosternal carinae about as long as 2/3‒3/4 of prosternum, indistinctly arcuate, slightly convex mesally; notosternal carinae slightly curved outwards and not reaching anterior prosternal margin, the latter lacking marginal carina and relatively shallowly emarginate.

Elytra ( Figs 286–287 ) together oval, with moderately strongly rounded sides, broadest near anterior third, EL 0.63–0.78 mm, EW 0.58–0.73 mm, EL/EW 1.03–1.12. Humerus with distinct callus; elytral punctures on variously large anteromedian adsutural region (usually as broad as 1/4‒1/2 of elytral width) very small and shallow and not arranged in longitudinal rows, those on side of each elytron moderately large but distinct, sharply marked, and partly arranged in irregular, not very distinct longitudinal rows, most punctures relatively dense, separated by spaces as wide as 1‒2 × their diameters. In a few specimens indistinct rows of large punctures (but smaller than those on sides) almost reach elytral suture.

Hind wings fully developed.

Mesoventral plate ( Fig. 290 ) with posterior portions of lateral longitudinal carinae forming an angle of ~20 degree with longitudinal body axis, and junction with metaventral femoral line is angulate; anterior margin of mesoventral plate straight or nearly so.

Metaventrite ( Fig. 290 ) with distinct, dense and numerous punctures on sides; median region with fine, inconspicuous setiferous punctures. Discrimen externally poorly marked.

Aedeagus ( Figs 291–292 ) 0.28 mm long, moderately slender; penis in lateral view almost evenly, curved; tegmen slender, narrowing from base toward apex, with relatively stout, subtriangular parameres which are about ~1.5 times as long as broad and each bears 5 long setae distributed from base to apex.

Distribution. Eastern North America from southern Ontario south to Florida and west to eastern Texas (Law- rence & Stephan 1975).

Remarks. Among species with recumbent dorsal pubescence and pronotal sides converging anterad from base, only M. depressus and M. pilifer are constantly light brown (in contrast to the dark brown M. piceus ). These two species are externally very similar, and small differences in the body silhouette and distribution of punctures may not be evident, unless series of specimens are directly compared. In most specimens of M. depressus , distinct (but not markedly large) punctures on the pronotum are mainly distributed in two irregular groups flanking large median impunctate region, and the flattened sides of pronotum bear only a few distinct punctures. In M. pilifer , distinct and dense large (but not conspicuously so) punctures are distributed on sides of pronotum, reaching each lateral carina, and only the median area is virtually impunctate. Similarly, distinct punctures are sparsely distributed on the median region of the abdominal ventrite 1 (in addition to denser and deeper large punctures on sides) in M. depressus , whereas in M. pilifer the median region of ventrite 1 is virtually impunctate and large punctures are restricted to sides of ventrite. These characters, however, are difficult to see under a stereomicroscope, and the character variability in M. pilifer , known from only a few specimens, remains unknown. The most reliable difference can be seen in the shape and setal pattern of the parameres: M. depressus parameres in lateral view are stout, ~1.5 times as long as broad, with setae distributed from near base, whereas in M. pilifer parameres in lateral view are slender, about ~3 times as long as broad, with setae only on their distal halves.

Figures

FIGURES 286–292. Morphological structures of Mychocerinus depressus (LeConte). Body in dorsal (286–287), ventral (288) and lateral (289) views; pterothorax in ventral view (290); and aedeagus (291–292).