Xenelmis uruzuensis

Manzo, Verónica, 2006, A review of the American species of Xenelmis Hinton (Coleoptera: Elmidae), with a new species from Argentina, Zootaxa 1242, pp. 53-68 : 65-67

Xenelmis uruzuensis

( Figs. 27–39 )

Body convex, rounded anteriorly, hemispheric in cross­section ( Fig. 27 ), length 3.4 mm, width 0.9 mm. Thoracic segments and first abdominal segments subequal in width, remaining abdominal segments progressively narrower. Cuticle dark brown; antennae, mouthparts and legs lighter in color.

Head: concealed by pronotum, anterior margin without teeth. Coronal suture short; frontal sutures long and curved, extending to base of antennae, frontoclypeal suture absent; margins of head capsule with several long setae. Gula well developed. Labrum subrectangular, transverse, with rounded anterior angles, basal third with row of short, ramose setae; distal margin with short setae and lateral margin with long setae. Labium ( Fig. 28 ) large, formed by prementum and postmentum. Postmentum large, subrectangular, longer than wide, basal and medial area with one pair of ramose setae; distal area with two pairs of ramose setae. Prementum membranous, short, transverse, anterior margin with short setae. Palpi three­segmented, segments subequal, apex of the last segment with short setae. Maxillae ( Fig. 29 ) with cardo subrectangular. Stipes long, subrectangular, distal third with three long setae on outer margin. Lacinia and galea well developed, lacinia as a strong lobe with 7 –8 blunt setae on mesal margin, galea onesegmented, elongated, with 4 apical setae. Palpi four­segmented, basal segment short, wider than long, second segment subrectangular, third segment slightly longer than second, with two apical setae, one on each side, last segment longest, rounded at apex with two sensoria. Mandibles ( Fig. 30 ) symmetrical, apex tridentate; inner margin with long, densely setose prostheca. Antennae ( Fig.31 ) short, three­segmented. Basal segment stout, second segment the longest, slender with distal long sensory filament. Third segment small, with short distal seta.

Thorax: ( Fig. 32 ) strongly sclerotized. Pro­, meso­ and metathoraces with light and dark areas as shown in figure 27, tergal plates with sagittal line. Pronotum convex, about twice as wide as long, with rounded angles, lateral margin with long setae (9 – 10); terga with setiferous tubercles as in figs 36, 37 and 38; on each side of sagittal line with two suboval patches devoid of setae (dotted line); pleural sclerite large, formed by episternum and epimeron, episterna meeting anteriorly at the midline, without posteromedial sclerite, procoxae open. Mesonotum and metanotum with sharp angles, produced posteriorly with several small marginal setae; pleural sclerite with epimeron and episternum divided into two parts. Meso­ and metasterna subtriangular, anterior margin almost straight. Legs ( Figs. 33, 34 and 35 ) five­segmented, similar in shape, those of prothorax the shortest. Coxa subtriangular, trochanter small, subtriangular, femur long and slender, tibia the longest segment, bearing hooked tarsungulus, all segments with setae as in figs 33–35.

Abdomen: Nine­segmented. Terga with setiferous tubercles like those of pronotum; terga 1–4 with sagittal line. Posterior angle of terga of first segment produced posteriorly with several small marginal spines; posterior angles of segments 2–7 with two strong spines and small setae; segment 8 with one spine and small setae. Ninth segment elongated and strongly emarginated, ending in two long lateral spinose processes. Segments 1–6 with pleura bounded by tergo and sterno pleural sutures; these sutures converging at apex of sixth segment. Sternal plate of first segment with small setae as in figure 32. Pleural and sternal sclerites with sparse setiferous tubercles. Ninth segment bearing gill chamber and operculum. Operculum pentagonal, outer surface with setae as in Fig. 39 .

Comparative notes

Based on original descriptions and drawings of X. bufo , and description of X. sandersoni , the larvae of X. uruzuensis can be distinguished from those species by: (1) long setae on lateral margin of pronotum; (2) posterior angles of pronotum emarginate; (3) posterior angles of the meso­ and metanotum sharp, produced posteriorly, with short setae without spines and (4) body largest.

Figures

FIGURES 27 – 39. X. uruzuensis sp. nov. larva: 27, habitus; 28, labium, 29, right maxilla; 30, left mandible; 31, right antenna; 32, thorax and first abdominal segment, ventral view; 33, prothoracic leg; 34, mesothoracic leg; 35, metathoracic leg; Figs. 36 – 38, setae from thorax and abdomen; 39, operculum, dorsal view. Scale bars: Fig. 27 = 0.50 mm, Figs. 28, 29 and 39 = 0.10 mm, Figs. 33, 34 and 35 = 0.20 mm.