Fontidessus toboganensis Miller & Spangler, 2008

Miller, Kelly B. & Montano, Elizabeth T., 2014, Review of the genus Fontidessus Miller & Spangler, 2008 (Coleoptera, Dytiscidae, Hydroporinae, Bidessini) with description of four new species, ZooKeys 426, pp. 65-85 : 72-74

Taxon classification Animalia Coleoptera Dytiscidae

Fontidessus toboganensis Miller & Spangler, 2008 Figs 4, 5, 13, 20, 27, 32

Fontidessus toboganensis Miller & Spangler, 2008: 48.

Type locality.

Venezuela, Territorio Federal Amazonas, 40km S Puerto Ayacucho, at El Tobogan, Coromoto.

Diagnosis.

Although small for diving beetles, this species is relatively large for the genus (Figs 4, 5, TL = 1.5-1.6 mm). The prosternal process is moderately broad and parallel-sided and has the apex broadly truncate (Fig. 13). The male genitalia are distinctive with the median lobe elongate, slender and broadly recurved in lateral aspect (Fig. 27C). There is an elongate ventral sclerite that fits into the ventral groove of the median lobe (Figs 27B, C). Specimens are variable in coloration with specimens from Suriname indistinctly marked with maculae (Fig. 4) and specimens from Venezuela marked with diffuse but distinctive maculae on the elytra (Fig. 5).

Redescription.

Measurements. TL = 1.5-1.6 mm, GW = 0.8-0.9 mm, PW = 0.6-0.7 mm, HW = 0.4-0.5 mm, EW = 0.3-0.4 mm, TL/GW = 1.8-1.7, HW/EW = 1.6-1.7. Body (Figs 4, 5) oval, elongate; lateral outline nearly continuous between pronotum and elytron; lateral margins of pronotum gently curved; lateral margins of elytron evenly and gently curved.

Coloration. Head yellow brown, pronotum yellow brown, brown medially along posterior margin; elytron brown with the following yellow maculae: 1) a basal macula in a band extending from lateral to sutural margins, posterior margin of macula irregular, often with medial extension posteriorly along elytral suture, 2) a lateral longitudinal macula at humeral angle, 3) a narrow longitudinal macula along lateral margin medially, and 4) a subtriangular subapical macula (Figs 4, 5). Many specimens with elytral maculae reduced or indistinct (Fig. 4). Ventral surfaces of thorax and abdomen brown except prosternum, prosternal process, propleuron and pronotal epipleuron yellow-brown; appendages yellow to yellow-brown.

Sculpture and structure. Head with very fine, inconspicuous, irregular punctation, surface between punctures shiny with indistinct microsculpture in the form of small cells; eyes medium in size (Figs 4, 5, HW/EW = 1.6-1.7). Pronotal surface similar to that of head; with posterior angles obtuse; lateral bead narrow, of even width throughout; pronotal striae finely incised, extending nearly 1/2 distance across pronotum (Figs 4, 5). Elytron with anterolateral angle obtuse, not extended anteriorly (Figs 4, 5); surface similar to pronotum. Prosternal process broad, lateral margins subparallel, apex of process broadly rounded (Fig. 13); metacoxal process with lateral lobe minute. Pro- and mesotarsi relatively narrow in both male and female, but slightly broader in male. Metatrochanter very large relative to metafemur (Fig. 20).

Male genitalia. Median lobe in dorsal aspect elongate, slender, apically terminating in two elongate, narrow rami with medial deep, narrow emargination, long apicies distinctly expanded laterally (Fig. 27A); in lateral aspect slender, elongate, conspicuously recurved with apical portion very slender and apically narrowly pointed (Fig. 27C); with elongate ventral sclerite that is pointed apically (Fig. 27B). Lateral lobes elongate, apically slightly curved and narrowly rounded (Fig. 27D).

Female genitalia. Bursa copulatrix elongate and narrow; spermathecal duct long, slender, somewhat coiled, expanded before receptacle; receptacle small, about half size of spermatheca, intermediate duct between receptacle and spermatheca broad; spermatheca globular, spermathecal spine prominent, but not elongate; fertilization duct elongate, tightly curved in spiral, attaching to large fertilization sac; vagina elongate, moderately narrow; gonocoxae elongate, slender with abrupt, small, triangular expansion at apex.

Variation.

This species exhibits considerable variability in the extent of yellow coloration on the dorsal surface. Specimens from Venezuela are usually heavily marked with yellow maculae and fasciae on the elytron and have the pronotum and head yellow (Fig. 5). Specimens from Suriname, in contrast, have the elytral maculae reduced and very indistinct and the head and pronotum darker (Fig. 4).

Distribution and habitat.

Fontidessus toboganensis is known from the extreme western margin of the Guayana Shield in the area around Puerto Ayacucho, Venezuela and from a few localities in Suriname (Fig. 32). In both areas it is extremely common and abundant in hygropetric habitats. The broadly disjunct distribution and differences in coloration suggest the possibility that the two populations are different species, but the male genitalia are shaped the same and the body is similarly shaped and sized. This is similar to Fontidessus ornatus which is also darker and less maculate in eastern localities than in western ones, though that species is also known from localities in between.

Material examined.

~627 specimens from the following localities: VENEZUELA: Amazonas: 40km S Puerto Ayacucho, El Tobogan, Caño Coromoto 5.38678°N, 67.61537°W; nr Iboruwa: Tobogancito, 5.8069°N, 67.43855°W; Bolivar: Los Pijiguaos at rock outcrop, 6.59361°N, 66.82063°W. SURINAME: Sipaliwini District, Raleighfallen Nature Reserve plateau below Voltzberg, seepage, 4.68276°N, 56.1877°W. Sipaliwini District, Tafelberg Summit, nr Augustus Creek Camp, large seepage area, 3°55.600'N, 56°11.300'W 600m; Sipaliwini District, Tafelberg Summit, near Caiman Creek Camp, washing seepage, 3°53.942'N, 56°10.849'W, 733m.