Promecostethus unifalculatus Enderlein, 1909

Porto, Willians & Pérez-González, Abel, 2020, Redescription of Promecostethus unifalculatus, the only known harvestman from Crozet Islands (Opiliones: Triaenonychidae), Zootaxa 4861 (1), pp. 120-130 : 123-128

Promecostethus unifalculatus Enderlein, 1909

( Figs 2–6 )

urn:lsid:zoobank.org:act:02622972-F8A8-4142-81BE-E5A6A915F844

Promecostethus unifalculatus Enderlein 1909: 535–538 , figs 1–7; Roewer 1915: 167; Roewer 1923: 631; Kury et al. 2014: 4. Nuncia unifalculata: Hickman 1939: 160 , figs 1–16; Fage 1940: 283, Forster 1954:17; Maury 1990:103.

Types: 1 juvenile syntype from “Possession-Insel. Weihnachtsbucht” [ Possession Island , Christmas Bay], Crozet Islands, French Southern and Antarctic Lands, 25.xii.1901, E. Vaxhöffen ( ZMB, not examined) ; 3 juvenile syntypes from the same locality collected in moss cushions by E. Werth (without further data) ( ZMB, not examined) .

Material examined: 1 male, 3 females, Crozet Island , II 1986, J. Ledoux (MACN-Ar) . 1 male ( SEM voucher), same data (MACN-Ar) .

Redescription of male (MACN-Ar): Measurements: Total body length 4.80, carapace length 1.95, mesotergal length 2.93, carapace maximum width 1.85, mesotergal scute maximum width 2.52. Pedipalps: trochanter. 0.49, femur, 1.41, patella 0.73, tibia 0.94, tarsus 1.35.

Dorsum ( Figs 2 A, C ; 4 A–B): Scutum magnum outline hourglass–shaped with Eta (η) shape, without conspicu- ous ornamentations. Carapace with unarmed anterior margin. Ocularium elevated, conical, unarmed (i.e., without median acute apophysis) ( Figs 2 A, C ; 4 A–B). Mesotergal scutum with inconspicuous grooves, without clear delimitation of areas. Free tergites and anal operculum unarmed.

Venter ( Figs 2 E ; 4 C–D): Coxae I armed ventrally with two distal stout tubercles with subdistal setae, the remaining area covered by eight small tubercles with setae. ( Fig. 4 C–D). Coxae II bearing a row of four lateral tubercles with setae, the two distal are 2x larger than the two proximal; ventral side covered by small tubercles with setae. Coxae III with seven sparse tubercles with setae, a row of two tubercles with setae on the edge with coxae III and a row of four tubercles with setae on the edge with coxae IV. Coxae IV with a row of three ventral posterior tubercles with setae; sparse lateral tubercles with setae and one distal stout tubercle; projection of coxa IV near spiracles.

Chelicerae ( Figs 4 C–D; 5 A–B): With one dorsal meso-apical spiniform tubercle on basichelicerite and strong proximal boss. Cheliceral hand with nine meso-ventral tubercles with setae ( Fig. 5 A ), seven ectal tubercles with setae ( Fig. 5 B ) and 16 frontal tubercles with setae ( Fig. 4 C ).

Pedipalps ( Figs 5 C–D): Coxae with two setigerous tubercles. Trochanter with one ventral and one dorsal tubercle with setae. Femur robust, bearing three ventral stout tubercles, the proximal one with a subdistal seta and one ventral distal tubercle with setae. A dorsal row of four stout tubercles with subdistal setae and two small tubercles. Three small setigerous tubercles are located in the meso-distal side and a row of small setae is located at the mesobasal side. Patella with one small tubercle with setae and one seta on the ectal side, three sparse setae and one stout tubercle with subdistal setae on the mesal side. Tibia with a row of three mesal and ectal tubercles with a subdistal seta. An ectal row of small tubercles with a subdistal seta. Tarsus with a row of three ectal and mesal stout tubercles with subdistal setae, the ectal row starts with a small tubercle bearing a subdistal seta. Sparse setae in the dorsal and ventral sides.

Legs ( Figs 5 E–F): Trochanter I armed with a dorsal and five ventral tubercles. Trochanter II with four small ventral tubercles, III–IV smooth. Femur I covered by a row of ventral tubercles. Femur II–IV with sparse setae. Patella and tibia, I–IV with sparse setae. Metatarsus with astragalus almost three times larger than calcaneus on leg I, at least five times larger on legs II–IV. Claws of legs 3–4 trifurcated. Tarsal count: 4:7–8:4:4.

Genitalia ( Figs 3 ; 6 ): Pars distalis with a large ventral plate with an arc shape, bearing one dorsal superior seta and three ventral inferior setae on each side of the ventral plate. Glans with a capsula externa forming a dorsal plate with a wide median cleft, dividing the dorsal plate into two halves. Capsula interna larger than capsula externa. Capsula interna with fused conductors that are not fused with the stylus, but covering the stylus in ventral and lateral surfaces, microsculpture present in the lateral surface of the conductors. Apical part of the stylus exposed in ventral and dorsal views; stylus curved ventrally.

Description of female. (MACN-Ar): Measurements. Total body length 4.00, carapace length 1.43, mesotergal length 2.60, carapace maximum width 1.44, mesotergal scute maximum width 2.32. Pedipalps: trochanter. 0.27, femur, 1.06, patella 0.55, tibia 0.73, tarsus 0.88.

Similar to male in relation to the armature of the dorsal scutum ( Figs 2 B, D, F ). Female pedipalps markedly smaller in size and with sexual dimorphism in the proximal ventral tubercle of femur, which is acute in females and becomes broader towards the apex (see Hickman 1939, p. 161 figs 3–4). Posterior edge of carapace shorter than male.

Distribution. Possession Islands, Crozet Islands, French Subantarctic Lands

Figures

FIGURE 2. Promecostethus unifalculatus, habitus: dorsal, lateral and ventral views: A, C, E male; B, D, F female. Scale bars = 2 mm.

FIGURE 3. Penis of Promecostethus unifalculatus, A, ventral view; B lateral view; C dorsal view. Scale bars 100 μm.

FIGURE 4. Promecostethus unifalculatus: SEM images of the male habitus: A, dorsal view; B, lateral view; C–D, ventral views. Scale bars = A–C 1 mm; D 500 μm.

FIGURE 5. Promecostethus unifalculatus: SEM images of male appendages; chelicerae: A, mesal view; B, ectal view; pedipalps: C, mesal view; D, ectal view; legs: E, detail of claw IV; F, prolateral view of leg IV. Scale bars = A–D, F 500 μm; E 100 μm.

FIGURE 6. Promecostethus unifalculatus: SEM images of penis:A–C ventral view; D–F lateral view; G–I dorsal view; J apical view. Scale bars = A, D, G 200 μm; B, H 100 μm; E, J 50 μm; C, F, I 20 μm.