Potamophilops cinereus (Blanchard, 1841)

Vanin, Sergio Antonio & Costa, Cleide, 2011, Description of the larva of Potamophilops cinereus (Blanchard) from Southeastern Brazil (Coleoptera, Elmidae, Larainae), Zootaxa 2808, pp. 57-63 : 58-61

Potamophilops cinereus (Blanchard, 1841)

(Figs. 3–19)

Larva description (Figs). Length 11 mm. Body elongate ovate, subcylindrical, moderately convex dorsally and flattened ventrally, subtriangular in cross section; lateral margins of pro-, meso-, metathoracic and abdominal segments moderately flattened and expanded laterally, margins of abdominal segments broadly rounded and bordered by large setae. Tegument reddish brown, densely covered with light yellowish brown, felt-like scales.

Head (Figs. 1–2, 5–8, 10), when seen from above, concealed by anterior projection of pronotum; about as long as wide, covered by scales except for a narrow basal band, frontal suture V-shaped, inconspicuous (Fig. 10); five clustered stemmata on each side (Fig. 11), upper four very approximate and aligned forming an arch. Antennae (Fig. 12) three segmented, basal segment slightly longer than wide, with two distal clusters of setiform and spatulate setae, second segment about twice as long as first, slender, with a short apical seta and with an elongate sensorium, subequal in length to the small third segment. Frontoclypeal suture well developed. Labrum (Fig. 13) transverse, anterior margin sinuous, lateral margins rounded, with a fringe of dense, long, branched setae, increasing in size from middle toward sides; each basal angle with a large, broad and pilose scale. Epipharynx (Fig. 14) densely setose in front and on lateral sides, leaving two small anterior and a large central area glabrous; central area with two lateral clusters of four sensillae. Mandibles (Figs. 15–17) symmetrical with three obtuse teeth, being two apical and one subapical; outer margin with five long branched setae and with a row of about eight short spatulate setae; prostheca long, with about 3/5 of mandible length, slender and pilose. Maxilla (Fig. 18) with four segmented palpi, first and second palpomeres subequal, third longest and about as long as length of first and second combined, fourth smaller; stipes without palpifer, distally with about four long branched setae and two long curved setae, outer margin covered by microtrichiae; cardo small (not represented in the figure), triangular, transverse; galea and lacinia separated, each one densely setose and with a few spatulate setae apically. Labium (Fig. 19) elongate, with palpiger and two segmented palpi, slightly shorter than maxillary palpi; palpiger membranous, broader and slightly longer than first globose segment; second segment subcylindrical, smaller and much more slender than preceding segment, with distal, scattered, short, peg like sensillae; ligula transverse forming four lobes, each one of anterior lobes with two small sensilla, one spatulate and other bearing a minute seta, each one of posterior lobes with a rounded sensilla; mentum long, about twice as long as wide, with a blunt seta near the anterior angle, a much longer and curved setae placed just behind, and a distal irregular stripe of long branched setae; submentum short (not represented in the figure), transverse and indistinct. Gula well developed.

Thorax (Figs. 3–8). Pronotum trapezoidal, transverse, about 0.7 X as broad as long, widest near base, sides arcuate, constricted near anterior third and with a transverse impression, anterior margin notched at middle, strongly produced and forming a projection that conceals head when seen from above. Prothoracic tergum with four signa and six sinuous longitudinal rows of seta-bearing tubercles, two outer rows very short, divergent and placed near posterior angle of pronotum, two median rows not surpassing transverse impression, two inner rows extending nearly full length of pronotum; meso- and metathoracic terga with four signa and six sinuous longitudinal rows of seta-bearing tubercles, outer pair of rows continuous and extending full length of terga, remainder interrupted near middle of length; mesothorax with anterolateral spiracles.

Abdomen (Figs. 3–7, 9) with nine segments; segments 1–8 expanded laterally, margins broadly rounded and bordered by large setae; terga 1–8 each with four rows of seta-bearing tubercles similar to those on thorax; segment 9 tectiform, carinate at middle, elongate, about 2.2 X as long as broad, conical, constricted at base, emarginate apically. Spiracles on small conical tubercles, located anterolaterally on segments 1–8.

Venter (Figs. 4, 6, 9). Prothorax with seven sclerites, two anterior (prepleurite), two anterolateral (postpleurite, anterior part), two posterolateral (postpleurite, posterior part) and one between coxae; meso- and metathorax with five sclerites, one anterior, two anterolateral and two posterolateral; pro-, meso- and metathoracic coxal cavities open posteriorly. Legs (Figs. 7, 8) stout and short, not seen from above, five segmented, tibia with a ventral tuft of long setae, tarsungulus (claw) broad and strongly uncinate. Abdomen with sternopleural sclerites on segments 1–7 (Figs. 4, 6); ventral operculum trapezoidal (Figs. 4, 6–7, 9), about 2.2 X as long as broad, rounded at base, lateral margins subparallel to just beyond middle and then curved inwards to acute apex; opercular hooks curved, slender, their apices do not surpass apex of segment 9.

Material examined. BRAZIL. São Paulo. Ribeirão Grande, Fazenda Intervales, Rio Carmo, 11. XI. 1993, C. G. Froehlich & H. Paprocki cols. (2 larvae, one dissected), (10 adults, at light: 9 pinned, 1 in alcohol) ( MZSP); same locality, 18–19. XI. 1991 (5 adults, at light).

Biological notes. According to Dr. Froehlich (pers. comm.), who collected the specimens, the Rio Carmo has a rocky substrate and fast running waters. At the same station where the larvae of P. c i n e re u s were obtained, one adult of Dryopidae and two adults of another species of Elmidae were also collected. The adults were collected at night, in a light trap.

PLATE 1. FIGURE 1. Potamophilus cinereus (Blanchard, 1851) , habitus of adult.

PLATE 2. FIGURE 2. Potamophilus cinereus (Blanchard, 1851) , head of adult, frontal view.

PLATE 3. FIGURES 3–4. Potamophilus cinereus (Blanchard, 1851) , habitus of last instar larva, (3) dorsal and (4) ventral views.

PLATE 4. FIGURES 5–9. Potamophilus cinereus (Blanchard, 1851) , last instar larva, (5) dorsal, (6) ventral and (7) lateral views; (8) detail of prothorax, lateral view; (9) detail of abdominal segments 8 and 9, ventral view.

Very little is known of the natural history of P. c i n e re u s. According to Brown (1981, 1987), adult laraines lack plastrons and are typically riparian rather than aquatic. However, adults of some genera, such as the African Potamodytes and the Neotropical Hispaniolara and Potamophilops , are able to maintain a respiratory bubble on the pubescence of the integument and may remain indefinitely beneath the water. Brown (1987) reported the presence of larvae of Chironomidae (Diptera) on some larvae of Potamophilops in Brazil.

Geographic distribution. Spangler & Santiago (1987, fig. 173) reported Potamophilops cinereus from Argentina and Brazil, in the State of Mato Grosso do Sul (Rancho Grande). Thus the present record for the State of São Paulo (Ribeirão Grande) widens considerably eastwards the geographic range of the species.