Luchoelmis kapenkemkensis

Archangelsky, Miguel & Brand, Cecilia, 2014, A new species of Luchoelmis Spangler & Staines (Coleoptera: Elmidae) from Argentina and its probable larva, Zootaxa 3779 (5), pp. 563-572 : 567-572

Luchoelmis kapenkemkensis mature larva

Description. Body ( Figs 12 , 23, 24 ) elongate, sides subparallel, widest at thorax, abdominal segments narrowing towards posterior end; body subtriangular in cross-section. Dorsal surface of thorax and abdomen strongly tuberculate, tubercles arranged in longitudinal rows. Color reddish-brown. Length: 3.5–3.9 mm; maximum width: 0.65–0.70 mm.

Head capsule ( Figs 12, 13 ) exposed, not covered by pronotum, anterior margin lacking tooth between base of antenna and clypeus. Surface with several large tubercles on disc, close to frontal lines. Coronal line very short, frontal lines long, extending to inner margin of antennal sockets. Fronto-clypeal suture present, feeble. Gula subtrapezoidal, narrower than maxillolabial complex; basal margin wider and concave, distal margin narrower and convex. Five stemmata on each side of head at about midlength.

Labrum ( Figs 15, 16 ) subrectangular, slightly wider in anterior third; anterior margin slightly concave, anterolateral margins rounded, each with a row of three strong dorsal ramose setae. Six strong ramose setae arranged in a transverse row in anterior third on dorsal surface. Ventral surface with anterior row of ramose setae, rest of ventral surface covered by short pubescence oriented mediad and posteriorly.

Antennae ( Figs 13, 14 ) short, three-segmented, located on anterolateral corners of head capsule. Basal antennomere short and wide, apically with a crown of ramose setae. Second antennomere the longest, cylindrical, with a few distal setae, bearing a short sensorioum. Third antennomere the shortest, shorter than sensorium of second antennomere, bearing a long apical seta.

Mandibles ( Figs 17, 18 ) symmetrical, apex with three blunt teeth. Dorsal surface with inner margin straight and sharp. Ventral surface with inner margin concave, with a comb of long stout submarginal setae. Inner margin of mandible with long setose prostheca; outer margin with two large ramose setae close to midlength.

Maxillae ( Figs 19, 21 ): cardo narrow, irregularly suboval, transverse, with a stout seta close to outer margin. Stipes the largest segment, subrectangular, 2.6 times as long as wide; distal third with several setae distributed as follows: two long setae on outer margin (distal one ramose), inner margin with one short stout seta, distal margin with one ramose seta close to base of lacinia. Lacinia and galea well developed; lacinia subtriangular, fused to stipes, with inner margin bearing a group of stout setae; galea 1-segmented, shorter than lacinia, elongate, with several apical setae. Palpus four-segmented, first palpomere the shortest, remaining three palpomeres subequal in length, last palpomere bearing several short apical setae and sensoria.

Labium ( Figs 19, 21 ) large, subdivided into a large postmentum and a short prementum, forming together with maxillae the maxilla-labial complex. Postmentum subrectangular, 1.6 times as long as wide, ventral surface with several short ramose setae at each side of middline; basal corners each with a large and stout seta; distal corners each with a large ramose seta. Prementum short, poorly sclerotized, wider than long, distal margins densely setose. Palps two-segmented basal palpomere slightly shorter, distal palpomere with several distal setae and sensoria.

Thorax ( Figs 12 , 20 , 22 ) strongly sclerotized; tergal plates with sagittal lines and with large tubercles arranged in longitudinal rows, those on pronotum sinuous. Prothorax the largest segment, pronotum subtrapezoidal, anterior and posterior corners rounded; ventral region with seven sclerites: one large and irregularly shaped transverse anterolateral pair, one small, triangular lateral pair, one large posterior pair and one small suboval sclerite between procoxae; coxal cavities open. Meso- and metathorax shorter than prothorax, twice as wide as long; each segment ventrally with five sclerites: one large anterior subpentagonal sclerite, and two smaller subrectangular sclerites on each side; coxal cavities open. Legs five-segmetned; coxa the largest segment, subtriangular; trochanter smaller, subtriangular; femur and tibia elongate, femur slightly longer and wider than tibia; claw stout, slightly shorter than tibia.

Abdomen ( Figs 12 , 23–26 ) well sclerotized, composed of nine segments, tapering towards posterior end; segments I–VII with sagittal line, subequal in length; segment IX the longest. Tergal plates with setiferous tubercles arranged in eight longitudinal rows on segments I–VI, three rows above spiracle and one row of smaller tubercles below spiracle; segments VII–VIII with six longitudinal rows; segment IX with three rows of tubercles, one dorsal and two lateral; all tubercles bearing large comb-like setae. Pleural sclerites present on segments I–V; sterna of segments I–V subrectangular, wider than long. Segment IX elongate, 3.4 times as long as previous segment, bearing a dorsal keel, apex slightly emarginated; sternal area with apical gill chamber, operculum subtriangular, sharply pointed, covering a pair of strong distal hooks bearing an inner row of sharp spines on inner margin and several long setae on outer margin. Spiracles present on segments I–VIII, those of segments I–VI much larger.

Comparative notes. Adults of L. kapenkemkensis display several characters not found in the other known species of the genus, i.e. color pattern, abdominal plastron and cleaning fringes on meso- and metatibiae. These characters make L. kapenkemkensis markedly different from the remaining species, but at the same time it also shows most of the generic diagnostic characters defining Luchoelmis (with the exception of the tibial cleaning fringes, but see below). Based on this we think, that L. kapenkemkensis could represent a distinct species within Luchoelmis , something that could explain the strong differences found in the larvae. It is worth mentioning here that the L. cekalovici specimens we examined also have cleaning fringes on the meso- and metatibiae, something that contradicts the original description of Spangler and Staines (2002).

Larval differences between L. kapenkemkensis and L. cekalovici are very pronounced. This is something that at a first glance called our attention, and made us doubt of the association with adults of L. kapenkemkensis , but after seven years of fieldwork no other elmid adults and larvae have appeared at this locality ( L. cekalovici larvae were associated with adults by rearing). Looking into the literature, significant differences in larval morphology among species of the same genus have been reported in Australia ( Glaister 1999). Within the genera Notriolus Carter & Zeck and Simsonia Carter & Zeck very marked differences in thoracic and abdominal morphology have been detected ( Glaister 1999), and some of the differences found in these Australian genera are similar to those found between L. cekalovici and L. kapenkemkensis (e.g. number of pleural sclerites, presence and arrangement of tergal tubercles). Therefore we suggest that Luchoelmis could also show a diverse larval morphology.

Larvae of L. kapenkemkensis can be distinguished from those of L. cekalovici by the following combination of characters: 1) pleural sclerites on first five abdominal segments (on first four in L. cekalovici ); 2) thoracic and abdominal terga with large tubercles arranged in longitudinal rows (absent in L. cekalovici ); 3) operculum subtriangular (subpentagonal in L. cekalovici ).

Larvae of L. kapenkemkensis could be mistaken with those of Stethelmis due to the presence of pleural sclerites on the first five abdominal segments; actually they would key out as Stethelmis in the keys of Manzo & Archangelsky (2008) and Archangelsky et al. (2009). The following characters will easily separate larvae of these two genera: 1) anterior margin of head capsule lacking tooth between base of antenna and clypeus (present in Stethelmis ); 2) thoracic and abdominal terga with large tubercles arranged in longitudinal rows, bearing long comblike setae (larvae of Stethelmis only have a row of tubercles bearing flat setae on the margins of the abdominal terga); 3) operculum subtriangular (subpentagonal in Stethelmis ); 4) color reddish-brown (dark brown in Stethelmis ); 5) abdominal terga I–VII with complete sagittal line (in Stethelmis complete sagittal line present only on abdominal segments I–III, on segments IV–V or IV–VI sagittal line incomplete).

Figures

FIGURES 12 – 16. Mature larva of Luchoelmis kapenkemkensis: 12) habitus, dorsolateral view; 13) head capsule, dorsal view; 14) antenna, dorsal view; 15) labrum, dorsal view; 16) labrum, ventral view. Scale bars, Fig. 12: 1 mm; Fig. 13: 0.1 mm; Figs 14 – 16: 0.05 mm.

FIGURES 22 – 26. Mature larva of Luchoelmis kapenkemkensis: 22) Thorax, ventral view; 23) detail of first five abdominal segments, dorsal view; 24) fourth abdominal segment, lateral view; 25) operculum of ninth abdominal segment, ventral view; 26) hooks of tracheal chamber. Scale bars: Figs 22, 23: 0.5 mm; Figs 24 – 26: 0.1 mm.

FIGURES 17 – 21. Mature larva of Luchoelmis kapenkemkensis: 17) mandible, ventral view; 18) mandible, dorsal view; 19) maxillolabial complex showing right maxilla and labium, ventral view; 20) mesothoracic leg; 21) detail of maxillolabial complex showing distal part of maxillae and labium. Scale bars, Figs 17 – 19: 0.05 mm; Fig. 20: 0.1 mm.