Harmoniconis one of the genera of the subfamily Diplurinae with a lyra prolaterally on the maxillae. It differs from Diplura by the shape of the lyra bristles (claviform in Diplura rather than hookshaped in Harmonicon), a more dense scopula on Ta I and II, the presence of a dense scopula in more than the apical third of pedipalpal tarsus, the presence of a scopula in the apical third of most leg metatarsi, and by the leg tarsi being pseudosegmented instead of showing only a few cracks. Harmonicon can be distinguished from Trechona by a less dense scopula on Ta III and IV, and by fewer lyra bristles arranged in a single row.

Cambridge (1896) and Maréchal and Marty (1998) regarded the presence of five lyra bristles a key feature for the genus. Research on the development on the new species described here showed that younger specimens have fewer lyra bristles than fully grown ones. Therefore the number of lyra bristles should no longer be considered diagnostic for Harmonicon. Maréchal and Marty (1998) stated that the leg formula of 1423 (rather than 4123 as in Diplura and Trechona C.L. Koch, 1850), is also a key feature of the genus Harmonicon, but show a leg formula of 4123 for the female holotype of Harmonicon audeae. Cambridge (1896) was incorrect in stating that the holotype of Harmonicon rufescens is a female; it is in fact a juvenile male. Maréchal and Marty (1998) did not comment on the putative synonyms of Harmonicon, Pseudohermachura Mello-Leitão, 1927 and Prosharmonicon Mello-Leitão, 1938, as well as those species formerly assigned to Harmonicon: Harmonicon nigridorsi Mello-Leitão, 1924 and Harmonicon riveti Simon, 1903. Mello-Leitão (1927) described the monotypical genus Pseudohermachura from a single female specimen of the type species Pseudohermachura catharinensis Mello-Leitão, 1927 (holotype deposited in MPSP) and did not mention the presence of a lyra at all. Bücherl (1962) redescribed Pseudohermachura catharinensis and mentioned a lyra consisting of 7–10 claviform bristles. Mello-Leitão (1938) described the monotypical genus Prosharmonicon from a single female specimen of the type species Prosharmonicon maculatum Mello-Leitão, 1938 (holotype deposited in IBSP and destroyed in the fire of 2010) and explicitly mentioned claviform lyra bristles. We therefore consider Pseudohermachura and Prosharmonicon junior synonyms of Diplura and reject the synonymies with Harmonicon established by Bücherl (1962). Simon (1903) described Harmonicon riveti from a single male specimen, of which the palpal organ, distal part of Ti I and basal part of Mt I were later illustrated in Berland (1913): pl. 7, fig. 5–6. The illustrations show a palpal organ with a strongly curved apex of the embolus and a highly elevated tubercle laterally in the basal third of Mt I. The morphology of the palpal organ and the tubercle in the basal third of Mt I in (known) males is different in those species currently assigned to Harmonicon. Mello-Leitão (1924) described Harmonicon nigridorsi from a single female specimen, he explicitly mentioned claviform lyra bristles, which is also supported by the illustration in Mello-Leitão (1926): fig. 4. We therefore support the transfer of those two species to Diplura by Raven (1985).

Male holotype and 1 female paratype (SMNK) from Saint Georges, French Guiana, 3°56'56.12"N, 51°47'39.90"W (leg. T. Vinmann).

PCD–33–306–03 1 imm of Harmonicon oiapoqueae, same data as for holotype and paratype.

The specific epithet, a feminine genitive singular, refers to the Oiapoque river, which is close to the type locality.

Harmonicon oiapoqueae sp. n. can be distinguished from the other species of the genus by the posterior pair of sternal sigilla being oval instead of circular. It furthermore differs from Harmonicon audeae by only one row of teeth on the tarsal claws of the pedipalp and from Harmonicon rufescens by a more stronly recurved, inverted U–shaped fovea and position and arrangement of cuspules on the basal inner corner of the maxillae. Harmonicon oiapoqueae sp. n. differs from Harmonicon audeae and Harmonicon rufescens by more slender legs III and IV in females and juveniles and legs I-IV in males. Furthermore, males can be distinguished from those of Harmonicon audeae by a shorter embolus and a wider bulbus [PL(100)/BD = 147] and the presence of a tubercle in the basal third of the lateral metatarsus I.

Male holotype: Colour in alcohol: carapace, legs and pedipalps mahagony brown, chelicerae red, opisthosoma grey. Carapace (length: 11.67; width: 10.38) covered with soft grey setae and longer, black setae in posterior thoracic area; margin with long, black setae and soft, silver setae; clypeus present, narrow; fovea slitlike, recurved, inverted U–shaped; striae marked. Chelicerae with two retrolateral bands of plumose setae and one dorsal band, broadening to full width of chelicerae distally; ventrally with one row of 9 teeth (1–1–1–1–5) on promargin; cheliceral furrow with a field of small basomesal teeth; retroventral base with isolated bristles. Maxillae with prolateral lyra consisting of 7 hookshaped bristles (as in the female paratype - viz. Fig. 6); ventrally with few cuspules on basal inner corner, number and arrangement different in both sides. Labium trapezoidal, without cuspules; labiosternal suture short and divided. Sternum with 3 pairs of sigilla: anterior pair at height of Co I, circular, medial pair at Co II, circular, posterior pair between Co III and IV, oval, largest; anterior and medial pairs almost equal in size. Legs long and slender (measurements and proportions in table 1), with all tarsi pseudosegmented (Ta IV missing). All present tarsi with dense and entire scopula; metatarsi also scopulated in apical third, but less dense. STC at Ta I and II truncated (maybe worn off), not curved; normal at Ta III, curved and long; all with few teeth; ITC short, without teeth. Ti I retroventrally at apex with megaspine (Fig. 4, 7); Mt I with a low, domed tubercle retroventrally in basal third (Fig. 7). Number and position of spines on legs different on both sides. Opisthosoma (length: 12.34; width: 7.15) with two pairs of spinnerets: PMS small, consisting of one segment (length: 3.96), widely separated from each other. PLS elongated, consisting of three segments: basal (length: 5.62), medial (length: 6.18), apical (length: 10.68) longest. Palpal bulb pyriform with relatively long, almost straight embolus (Figs 1, 2).

Female paratype: Colour in alcohol: resembles male holotype, but legs darker. Carapace (length: 13.26; width: 12.54) and opisthosoma (length: 17.37; width: 7.58) larger than that of holotype. Different from male holotype by the presence of one more labial cuspule and several more cuspules on basal inner corner of maxillae (Fig. 3). Chelicerae with more teeth on promargin (1–1–1–1–1–1–1–1–3). Lyra as in Fig. 6. Legs not as long and slender (measurements and proportions in table 1 in parenthesis). Pedipalpal tarsus with slight scopula, divided by two parallel rows of spiniform setae in apical third, becoming more irregular beyond apical third. Slight scopula on Ta I and II; divided by two parallel rows of spiniform setae. Mt I and II with scopula less dense only covering apical third, divided by two parallel rows of spiniform setae, becoming more irregular basally. Ta III like Ta I and II; Mt III without scopula, only with hairlike setae. Ta IV with only thin scopula and more setae, Mt IV like Mt III. Leg spination as in male holotype. Opisthosoma resembles male holotype, but with PMS (length: 3.27) more widely (by length of segment) seperated and basal segment of PLS (length: 5.12), medial (length: 4.44), apical (length: 8.55) slightly shorter. Vulva as in Fig. 5.

Although the number of lyra bristles varies during the development of this species, the paratype of Harmonicon oiapoqueae sp.nov. has more such bristles than the female holotype of Harmonicon audeae; both specimens are of almost the same size.

According to Thomas Vinmann (pers. comm.), who collected the specimens examined, females build large sheetwebs of ca. 2 m2 which are attached to branches of trees and bushes. The sheetweb runs into a funnel which leads to a ca. 20 cm deep tube–shaped retreat. The burrow leads about 5 cm vertically into the ground and continues for ca. 10 cm at an angle of about 45°. At dusk the spiders come to the entrance of the funnel and wait for prey.