Potamophilops bragaorum, Fernandes & Hamada, 2012

Fernandes, André Silva & Hamada, Neusa, 2012, Description and notes on the bionomics of a new species of Potamophilops Grouvelle, 1896 (Coleoptera: Elmidae: Larainae), from the Cerrado biome in Brazil, Journal of Natural History 46 (11 - 12), pp. 717-727 : 719-726

Potamophilops bragaorum sp. nov.

( Figures 2–4 )

Diagnosis

Body average length (pronotum and elytra) 6.08 mm (standard deviation 0.25); ventrite I without carinae between metacoxae; parameres of male genitalia without hairs or setae; median lobe of male genitalia with flat-topped and irregularly shaped lateral callosities; styli of female genitalia with apical segment measuring one-third the length of the basal segment.

Description

Holotype. Male ( Figures 2 , 3 , 4A–F, I ). Greatest length 6.32 mm and width (posterior third of elytra) 2.35 mm. Body ( Figures 2 , 3 ) elongated, subparallel, robust, densely pubescent, moderately convex dorsally.

Head ( Figures 2 , 3 ): Finely, densely punctuated; punctures separated by a distance approximately half their diameter; frontal margin slightly concave. Eyes moderately protuberant, laterally rounded, separated by a distance 1.5 times wider than eye diameter. Antenna with 11 segments; first two segments combined are four-fifths the length of the remaining segments combined; segments 3–11 form a club. Frontoclypeal suture present between bases of antennae. Clypeus rectangular, as long as and wider than labrum; anterior margin concave; lateral angles rounded. Labrum rectangular; anterior margin truncated; anterolateral angles rounded, with row of moderately long golden setae. Maxillary palpus with four segments; first segment very short, half the length of second segment; segments 2–4 subequal in length; last segment diagonally truncated at the apex, forming depressed surface on internal margin. Labial palpus with three segments; last segment swollen, twice as wide as second segment, as long as the remaining segments combined. Gula, at base, with the same width as the submentum and 2.5 times narrower at the apex.

Colour: Cuticle black, except base of head, first two segments of labial palpi, labium, maxillae, coxae, trochanters, bases of femora and centre of metaventrite, which are light to dark yellowish brown.

Thorax ( Figures 2 , 3 ): Pronotum ( Figures 2 , 3A ) wider at base (1.88 mm) than long (1.34 mm); wider at base than at apex (1.2 mm); with deep, transverse and complete impression across apical third; disc convex behind transverse impression; anterolateral angles obtuse; base strongly sinuated with small fovea (length, 0.13 mm) on each side of midline in front of scutellum; posterolateral angles slightly produced, subacute, depressed and flat, with a posterior shallow constriction adjacent to each angle; lateral margin trisinuated and smooth, with anterior deep constriction joining transverse impression, adjacent to each anterolateral angle; posterolateral angles; anterior margin broadly convex, extending over base of head; posterior margin with five arches, one narrow and one broad on each side in front of the elytron, and one narrow in front of scutellum. Elytra ( Figures 2 , 3A ) subparallel; longer (4.7 mm) than wide, (maximum width at basal third, 2.35 mm); humeral angle broadly rounded and tumid; without sublateral carinae; lateral margins smooth; disc with 10 rows of punctures separated by a distance equal to their diameters, half as wide as intervals between striae; apex rounded to slightly angulated and dehiscent. Scutellum ( Figures 2 , 3A ) slightly convex; subtriangular; wider than long; anterior margin convex; posterior angle rounded. Prosternum ( Figure 3B ) longer (0.8 mm) than wide (0.54) between procoxae (0.54 mm), with anterior margin truncated. Prosternal process with lateral margins almost parallel between procoxae; apex abruptly narrowed and ligulated, starting after procoxae. Mesoventrite ( Figure 3B ) almost twice as wide (0.98 mm) as long (0.53 mm) between mesocoxae; shorter than prosternum; posterior margin sinuated and convex at median region. Metaventrite ( Figure 3B ) with median, glabrous, longitudinal impression extending to basal half; anterior margin between mesocoxae concave; posterior margin between metacoxae concave; posterior portion in front of metacoxae with transverse arched impression on each side. Legs ( Figure 2 ) long and slender; pro- meso- and metacoxae well separated, with mesocoxae more separated; mesotibiae with lateral surface poorly pubescent; metatibiae entirely and densely pubescent, except for alutaceous ventral surface. Tarsal claws well developed, long, without basal teeth.

Abdomen ( Figure 3B ): Longer (3.22 mm) than wide (maximum width, ventrite I, 2.28 mm). Ventrite I ( Figure 3B ) with anterior margin moderately impressed, subtriangular between metacoxae; without carinae or impressions. Ventrite V ( Figures 3B , 4I ) densely pubescent with moderately long hair-like setae (longer in the posteromedial region) extending beyond posterior margin; posterior margin sinuated, with moderately broad and deep concavity in the median region. Sternite VIII ( Figure 4G ) with long and slender anterior region; anterior angle subacute; lateral angles slightly acute and pointed backward diagonally; posterior region covered with medium to long hairlike setae; posterior margin sinuous, with angles rounded and a deep concavity in the median region. Spicule ( Figure 4E ) long and slender, bifurcated at the middle; apical margin with few hair-like setae; paraprocts extending beyond apical margin of spicule.

Male genitalia ( Figure 4A–D ): Paramere ( Figure 4A,B ) short, less than 0.5 times the length of median lobe; moderately broad and rounded at base; narrowed towards the apex; apex subacute. Median lobe ( Figure 4A–D ) long and slender; in dorsal view ( Figure 4A ) wider than paramere; with dark stripe beginning at the same line of paramere’s apex and extending until the apex of median lobe; lateral margins sinuous and irregular, with asymmetrical callosities on each side; widened in the median region; apex ligulated. Median lobe in lateral view ( Figure 4C,D ) long and slender, curved to the venter, slightly widened in the median region and then narrowed towards the apex. Left face of median lobe ( Figure 4C ) with callosity beginning across median region of median lobe; callosity with upper shallow excavation and outer ventral margin with granules. Right face of median lobe ( Figure 4D ) with callosity beginning above median region of median lobe; callosity with moderately deep excavation and inner ventral margin with granules. Basal lobe ( Figure 4A,B ) longer than median lobe and slender; almost parallel from the base to the median region, slightly widened in the median region and almost parallel from the median region to the apex.

Female. Externally similar to male except for the elytral apex (more angulated and weakly curved to the external side) and the ventrite V ( Figure 4J ) (narrower at the apex, less sinuous at middle of apical margin and slightly denser pubescence). Sternite VIII ( Figure 4H ) with anterior portion as long as wide; anterior margin truncated; lateral angles acute, curved outward and pointed backward diagonally; posterior end densely covered with medium to long hair-like setae; posterior margin with triangular angles and shallower, broad concavity in the median region.

Female genitalia ( Figure 4F ): Coxites longer than styli; wider at base than long, with irregular shape that resembles a boot positioned diagonally. Styli short; basal segments curved and divergent, apical portion rounded and covered with setae that vary from slender to stout and that curve to the external side; apical segment weakly narrowed from the base to the apex, straight, cylindrical, with one-third the length of basal segment and pointed to the external side.

Intraspecific variation

Size range (n = 6): length 5.80–6.42 mm, greatest width 1.95–2.22 mm. Aside from the secondary sexual characters, the specimens examined did not have significant morphological variation.

Comparative notes

Potamophilops bragaorum sp. nov. can be distinguished from P. cinereus by the smaller size (maximum 6.42 mm from the known specimens, compared with 7.0 mm for the P. cinereus holotype); by the coloration of first two maxillary palpi, mesotibiae and ventrite I behind metacoxae (black, instead of reddish-brown in P. cinereus ); by the absence of carinae on ventrite I (instead of poorly defined carinae between the metacoxae in P. cinereus ); by the absence of hairs on parameres of male genitalia (instead of short hairs present on lateral sides of parameres in P. cinereus ); by the flattened and irregular lateral callosities on the median lobe of male genitalia (instead of rounded and well-defined callosities in P. cinereus ); by the styli of female genitalia, with apical segment measuring one-third the length of the basal segment (instead of one-quarter the length of the basal segment in P. cinereus ).

Type locality

Ribeirão São João stream, Vai-Quem-Quer valley, Taquaruçú district, Palmas municipality, Tocantins state (TO), Brazil (10 ◦ 23 ′ 43" S, 48 ◦ 07 ′ 55" W) .

Type series

Holotype. Male (genitalia illustrated) BRAZIL: TO: Palmas , Taquaruçú , Vale do Vai- Quem-Quer, Ribeirão São João, 10 ◦ 23 ′ 43" S, 48 ◦ 07 ′ 55" W, manual collection, A.S. Fernandes leg., 28 December 2008 ( INPA).

Paratypes. One male, same data as holotype ( INPA) ; one female (genitalia illustrated), same data as holotype ( INPA) ; one male, same data as holotype ( DZRJ) ; one female, same data as holotype ( DZRJ) ; one male, same data as holotype ( NMNH) .

Etymology

The species epithet, bragaorum , is in honour of the Braga family, who hosted the senior author and provided transport during his fieldwork in Tocantins, Brazil.

Bionomics

The type series was collected inside (depths around 0.05–0.5 m) or beside (rocks and logs) a stream, around 5 m in width, with a bedrock streambed in a mountainous area of the Cerrado biome, in the Central–West region of Brazil ( Figure 5A,B ). Specimens of P. bragaorum sp. nov. were found inhabiting different microhabitats; some were taken from the riparian zone (with their bodies completely dry) and others from completely submerged logs in the main channel of the stream, at depths up to approximately 0.5 m. A few specimens were also collected while they were climbing ( Figure 5C ) against the strong water flow, on the rocky base of a small cascade ( Figure 5B ). Similar habitats were described by Spangler and Santiago (1987) for Disersus Sharp, 1882 and Pseudodisersus Brown, 1981 .

Preliminary examination of the gut contents of four individuals revealed a poor diversity of items. Identifiable material was mainly diatoms, with no recognized fungal spores or hyphae. We conclude that the main food sources of P. bragaorum sp. nov. are general detritus (unidentified) and unicellular algae (diatoms). Despite being unable to identify the algae to the species level, we recognized at least three genera of diatoms: Gomphonema Ehremberg, Eunotia Ehremberg and a genus in the family Cymbellaceae , probably Encyonema Kützing. It seems clear that, as observed in Lara avara LeConte, 1852 , adults of P. bragaorum sp. nov. are scrapers, obtaining nutrients by ingesting the microbial layer that adheres to wet or submerged wood and rocks (periphyton) ( Steedman and Anderson 1985).

Potamophilops adults seem to have habits similar to those of other Neotropical Larainae. They are riparian beetles, capable of entering the water and staying submerged for a long time, probably until the air reservoir in their elytra is exhausted ( Brown 1987), and they can fly actively as described by Hinton (1940) and Spangler and Santiago (1987).

Spangler and Santiago (1987), observing individuals of Disersus entering the water at times, suggested that they could be either ovipositing females or adults foraging on periphyton. As we found a great abundance of periphyton in the gut contents of P. bragaorum sp. nov., this foraging suggestion can be corroborated for Potamophilops .

Sometimes more than five individuals were seen together out of the water. However, no mating couples were observed during the short duration of our field observations.

Figures

Figure 2. Potamophilops bragaorum sp. nov., holotype habitus. Scale bar 2.00 mm.

Figure 3. Potamophilops bragaorum sp. nov., holotype in detail. (A) Dorsal view; (B) ventral view. Scale bar 2.00 mm.

Figure 4. Potamophilops bragaorum sp. nov. (A) Male genitalia, dorsal view; (B) male genitalia, ventral view; (C) male genitalia, left face of median lobe; (D) male genitalia, right face of median lobe; (E) spicule of male; (F) female genitalia, ventral view; (G) male sternite VIII; (H) female sternite VIII; (I) posterior end of male ventrite V; (J) posterior end of female ventrite V. Scale bar 0.50 mm.

Figure 5. Potamophilops bragaorum sp. nov. (A) Vai-Quem-Quer valley, Taquaruçú district, Palmas municipality, Tocantins state, Brazil; (B) cascade on the Ribeirão São João stream in the Vai-Quem-Quer valley, type locality of the new species; (C) P. bragaorum sp. nov. out of the water, as found in nature.