Amphicnemis hoisen Dow, Choong & Ng, 2010

Dow, Rory A., Gesriantuti, N. & Lupiyaningdyah, P., 2025, A new species of Amphicnemis Selys, 1863 from Sumatra, Indonesia and first records of two other species of Amphicnemis for the island (Odonata: Zygoptera: Coenagrionidae), Zootaxa 5659 (2), pp. 273-282 : 276-277

Amphicnemis hoisen Dow, Choong & Ng, 2010

Sumatran material examined. All from Kampar Peninsula, Pelalawan, Riau, Sumatra, Indonesia, all sites in the range ca. 5–9 m a.s.l.: 1 ♂ ( RER23 _COE35), flooded PSF beside Simpang Sianyir (tributary of Sungai Serkap) at 0.5035N, 102.5773E, 16 ii 2023, leg. R.A. Dow ; 1 ♀ ( RER23 _COE289), flooded PSF beside Simpang Sianyir (tributary of Sungai Serkap) at 0.5137N, 102.5508E, 1 x 2023, leg. R.A. Dow ; 1 ♂ ( RER20 _COE43) , 1 ♀ ( RER20 _ COE44), PSF (flooded by Sungai Serkap) behind fishermen’s huts downstream from ranger post, Sungai Serkap , 0.3613N, 102.7122E, 18 i 2020, leg. R.A. Dow ; 9 ♂♂ ( RER20 _COE45–53) , 2 ♀♀ ( RER20 _COE54–55), same location, 22 i 2020, leg. R.A. Dow ; 8 ♂♂ ( RER20 _COE56–63) , 4 ♀♀ ( RER20 _COE64–67), PSF (flooded by Sungai Serkap) between ranger post and Tasik Limau on Sungai Serkap , 0.3815N, 102.7154E, 26 i 2020, leg. R.A. Dow ; 1 ♀ ( RER20 _COE42), PSF on trail from Eco Camp to Sungai Serkap, 16 i 2020, leg. R.A. Dow .

Descriptive remarks. The series from the Kampar Peninsular is true to the type series of A. hoisen in most respects, but there are some structural differences in the male: the posterior spines of the genital valves are not quite as long as those of the type series, although they are still remarkably long and overlap the sternite of S10 to a variable extent. The downturned apical part of the upper branch of the cercus, seen laterally, appears slightly shorter than in the type series on average. All but one of the female specimens are immature, with a largely red thorax and legs, or semi-immature, retaining a reddish cast in the same areas. The females differ from the paratype described by Dow et al. (2010) in that almost the entire posterior pronotal lobe is black, with only a narrow area at the free margin and the lateral extremities paler, and also in that the sides of abdominal S9 are entirely pale, this extending dorsally apically. The Sumatran individuals are slightly larger on average than those from the type series.

Measurements (mm) of the most mature specimens. Males: abdomen plus anal appendages 32.5–35.5, Hw 20–21.5. Females: abdomen plus anal appendages and ovipositor 32–33, Hw 20–21.5.

Other remarks. During the surveys in the Kampar Peninsula A. hoisen has only been found in flooded or mostly flooded PSF adjacent to the Serkap River and its tributary Simpang Sianyir. It has not been found in PSF close to other rivers or remote from rivers even during the wettest periods when considerable amounts of surface water are present in the forest. This is in contrast to the habitat in which the type series of this species was collected at Sungai Bebar in Pahang, where it was found at discrete pools in PSF remote from any stream or river. At three of the five locations where it was found, A. hoisen appears to occur at relatively low densities but at the other two sites it was found to be relatively abundant during January 2020, actually during a protracted dry spell, but during a period of high water levels in Sungai Serkap due to tidal effects, so that the PSF was flooded around Sungai Serkap even though it was completely dry at sites remote from the river. The exact sites where the greatest numbers of individuals were found in January 2020 were not revisited during surveys at other times of year in 2023 due to time constraints, so it might be just as abundant at these sites in other periods.