Agabus riberae Bilton, Englund & Bergsten, 2020

Englund, William F., Njoroge, Laban, Bistroem, Olof, Miller, Kelly B., Bilton, David T. & Bergsten, Johannes, 2020, Taxonomic revision of the Afrotropical Agabus raffrayi species group with the description of four new species (Coleoptera, Dytiscidae), ZooKeys 963, pp. 45-79 : 45

publication ID	https://dx.doi.org/10.3897/zookeys.963.53470
publication LSID	lsid:zoobank.org:pub:9636C9F2-C6BD-4B34-BCC6-ED214C7B0D19
persistent identifier	https://treatment.plazi.org/id/A391EC84-95B1-480F-B4DD-E7DEA2AE3076
taxon LSID	lsid:zoobank.org:act:A391EC84-95B1-480F-B4DD-E7DEA2AE3076
treatment provided by	ZooKeys by Pensoft
scientific name	Agabus riberae Bilton, Englund & Bergsten
status	sp. nov.

Treatment

Agabus riberae Bilton, Englund & Bergsten sp. nov. Figures 1 View Figure 1 , 6E, F View Figure 6 , 8H View Figure 8 , 9E View Figure 9 , 11M View Figure 11 , 11Q View Figure 11 , 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 18 View Figure 18 , 19 View Figure 19

Type locality.

South Africa, Northern Cape Province, Kamiesberg, stream on Witwater-Langkloof Road ca 1 km S. of junction, 30°23'41.30"S 18°08'07.95"E, 1100 m.

Type material.

Holotype ♂ (AMG) labelled: "19/ix/2010 South Africa NC Kamiesberg Stream on Witwater-Langkloof road ca 1 km S. of junction. D.T. Bilton leg.". Paratypes: 5 ♂ 5 ♀ (CBP, SANC, ZSM) labelled: "19/ix/2010 South Africa NC Kamiesberg Stream on Witwater-Langkloof road ca 1 km S. of junction. D.T. Bilton leg."; paratype 4 ♂ 4 ♀ (AMG, CBP, ISAM, NHRS) labelled: "19/1x/2010 South Africa NC Kamiesberg - stream above Studer Pass ca 5 km W of Witwater 30°23'13.49"S, 18°07'05.78"E 1,105 m D T Bilton leg."; paratype 1 ♀ (IBE) labelled: "22/viii/2004 South Africa NC Kamiesberg - stream at top of Studer Pass G. Challet leg."; paratype ♂ (CBP) labelled: "19/ix/2014 South Africa NC Kamiesberg temporary stream in Kamiesberg Pass D T Bilton leg."; paratypes 2 ♂ (CBP) labelled: "18/ix/2014 South Africa NC Kamiesberg spring pool on Rondefontein Farm 30°30'05.59"S, 18°08'56.35"E 1023 m D T Bilton leg."; paratypes 4 ♂ 1 ♀ (CBP, NHRS) labelled: "17/ix/2014 South Africa NC Kamiesberg stream nr. Damsland on N. side of Rooiberg 30°23'36.33"S, 18°06'32.12"E 1111 m D T Bilton leg."; paratype 1 ♂ (CBP) labelled: 19/ix/2014 South Africa NC Kamiesberg stream nr. De Kuilen 30°10'44.94"S, 18°04'37.71"E 940 m D T Bilton leg."; paratypes 2 ♂ (CBP) labelled: "18/ix/2014 South Africa NC Kamiesberg - stream at bottom of Langkloof 30°33'16.98"S, 18°08'19.13"E 594 m D T Bilton leg."; paratypes 2 ♂ 4 ♀ (AMG, CBP) labelled: "28/ix/2018 South Africa WC Cederberg Tra-Tra river @ Wupperthal 32°16'45.35"S, 19°13'04.32"E 485 m D T Bilton leg.".

Diagnosis.

Very similar to A. austellus sp. nov., differing from this species in having a relatively broad metasternal wing (see Table 1 View Table 1 ), and an elytral microreticulation dominated by larger, more irregular meshes than seen in most A. austellus sp. nov. specimens (see above). Metatarsomere 5 is also somewhat longer in this species than in most A. austellus sp. nov.

Description.

Habitus as in Fig. 11M, Q View Figure 11 .

Colour: Head black with rufous interocular spots and an anterior rufous area. Pronotum black with rufous borders. Elytra rufopiceous to black. Ventral surface black, testaceous lines on abdominal segments rarely present, hypomeron and epipleuron rufotestaceous to rufous. Legs rufous to rufopiceous. Antennae and palpi testaceous.

Microreticulation : Relatively fine on both pronotum and elytra, and rather similarly impressed in both sexes. The microreticulation of the elytral disc is typically dominated by relatively large, somewhat irregular meshes (Fig. 9E View Figure 9 ).

Structural features : Body length: 7.21-8.24 mm (see Table 1 View Table 1 ). Hypomeron marginally visible in strict lateral view, lateral bead of pronotum narrow and well defined. Metasternal wing broad, WC/WS 3.0 or less in most specimens (see Table 1 View Table 1 and Fig. 12 View Figure 12 ). Pronotum broad, more than twice as broad as interocular distance (see Table 1 View Table 1 and Fig. 13 View Figure 13 ).

Legs: Male protarsal claws long,> 1.6 × as long as protarsomere 4 (see Table 2 View Table 2 and Fig. 14 View Figure 14 ). Metatarsomere 2 short and broad, <1.8 × as long as broad (see Table 2 View Table 2 ) in most specimens. Metatarsomere 5 long and slender,> 3.3 × as long as broad in most males (see Table 2 View Table 2 ).

Male genitalia: Tip of aedeagus short, lacking the prolongation of the area located between the subapical broadening and the apical and subapical tooth present in some species in the group (see Fig. 8H View Figure 8 ). There is some variation in the shape and size of the subapical tooth (Fig. 6E, F View Figure 6 ), this being relatively long and narrow in most specimens examined (Fig. 6F View Figure 6 ), but with both narrow and broader teeth being observed within the same population.

Female: Externally similar to males. Some specimens with dorsal microreticulation slightly more strongly impressed.

Distribution.

To date known only from Kamiesberg Range in the Northern Cape Province, and the eastern fringes of the Cederberg, Western Cape Province, Republic of South Africa (see Fig. 1 View Figure 1 ), material from both areas being confirmed from COI sequences. The Kamiesberg represents a northerly outlier of Fynbos and Renosterveld vegetation in predominantly arid Namaqualand, and consequently have a diverse flora with a number of localised endemics ( Helme and Desmet 2006). The mountains support the bulk of the global population of the endemic dytiscid Andex insignis Sharp, 1882 and a number of new, apparently endemic, water beetles have been described from the area in recent years ( Bilton 2013, 2015, 2016). Agabus riberae sp. nov. appears to be the only Agabus present in Kamiesberg, where it is abundant. In the Cederberg the species has been found close to Wupperthal, in the relatively dry northeastern fringes of the range. A. austellus sp. nov. is the only species so far recorded from the wetter central areas of the Cederberg. All sites known to date experience predominantly winter rainfall.

Ecology.

Found in streams and associated pools in the Kamiesberg and northeastern Cederberg ranges (Figs 18 View Figure 18 , 19 View Figure 19 ), in either Fynbos or Renosterveld vegetation between 480 and 1000 m elevation. Typically netted from marginal vegetation, including at the base of tussocks. Also found amongst grasses in a spring pool with cold water. Ecological differences between this species and A. austellus sp. nov. are unclear, but may relate, at least in part, to rainfall.

Etymology.

Named after our late friend and colleague Ignacio Ribera, who will be sorely missed.

Comments.

Despite the relatively minor morphological differences between this species and A. austellus sp. nov. we consider these two taxa distinct. COI sequences for four specimens of A. riberae sp. nov. investigated differed by 4.5-4.7% from A. austellus sp. nov., more than that observed between many well-established species in the subgenus Acatodes Thomson, 1859 (I. Ribera pers. comm.). This is supportive of the recognition as a distinct taxon, particularly given the relative uniformity in COI sequence observed across the wide geographical range of A. austellus sp. nov.