Glebych, Eskov & Marusik, 2021

Eskov, Kirill Y. & Marusik, Yuri M., 2021, Glebych minutissimus gen. et sp. nov., the smallest cobweb spider (Araneae Theridiidae), Zootaxa 5006 (1), pp. 45-53 : 46

Glebych gen. n.

Type species: Glebych minutissimus sp. n.

Etymology. The genus name is a patronym given in honor of our friend and colleague Kirill Glebovich Mikhailov, on the occasion of his 60 th birthday. The name is a friendly contraction of Mikhailov’s patronym, a Russian tradition used while addressing close friends or respected people; the gender is masculine.

Diagnosis (comparison of the generotypes). The new genus is most similar to Styposis Simon, 1894 and differs from it by having 6 bulged eyes (vs. 8, not bulged), carapace wider than long (vs. longer than wide), bulged sternum (vs. not modified), colulus distinct with 2 setae (vs. absent, replaced with 2 setae), having 3–4 cheliceral promarginal teeth (vs. 1–2), petiolus located at mid part of abdomen (vs. in anterior), tarsi longer than metatarsi (vs. shorter), cymbial spoor (Cs) with strong seta (Ss) ( Fig. 3A ), longer than hook (vs. absent), serrate median apophysis (vs. not serrate), epigyne with a kind of median plate (vs. absent, not documented). The new genus differs from all Theridiidae with documented tarsal organ by the proximal position of this organ – 0.7 (vs.<0.3).

Note. There are some other characters that may work for distinguishing Glebych gen. n. and Styposus like dimorphism in cheliceral indentation, e.g. 5 promarginal teeth in female and 3 in male, displaced tracheal spiracle, tegulum with retrolateral pit. These characters are not documented in the Styposis flavescens Simon, 1894 . Judging from the figures of male palp and epigyne, as well as the different number and sizes of eyes and shape of the abdomen it seems that Styposis is not monophyletic, and some of the species currently considered in it may belong to a separate, undescribed genus.

Another unique character is tarsi being longer than metatarsi; this characteristic has also been documented in the African and Palaearctic males of Tidarren Chamberlin & Ivie, 1934 , which have tarsi II–IV also longer than (or subequal to) metatarsi ( Knoflach & Harten 2006). Males of Tidarren are much smaller than females (cf. Knoflach & Harten 2006), and the New World members (both sexes) of the genus have metatarsi longer than tarsi.

Description

Small (body length 0.786–0.91), with 6 eyes in 2 triads, eyes strongly bulged, anterior median eyes totally reduced; pattern lacking; carapace high, about 1.5 times less that length, wider than long, covered with few setae; clypeus high; sternum wider than long; chelicera with kind of keel with 3 promarginal teeth in male ( Fig. 2G–H ), and 5 in female ( Fig. 2F ), with 2 setae near the base of fang ( Fig. 2F–H ); tarsi of legs equal (I) or longer than metatarsi (II–IV); tarsal organ (To) large, located proximally, its position ca. 0.7 ( Figs 1E , 4D ); female palp with bent claw with 3 teeth, 2 long and one short ( Fig. 4C ), tarsi in all legs in male with apparently toothless claws ( Fig. 4A, D ); petiolus located at the middle of the abdomen ( Fig. 1B, E ); book lungs apparently absent ( Figs 1B–E, F , 4K–L ); epigyne and epiandrus (Ea) sclerotized more heavily than surrounding cuticle; spiracle (Ts) slightly displaced anteriorly ( Figs 1C , 4E ); colulus (Cl) distinct, bearing 2 setae ( Figs 1C, F , 2D–E ); epiandrus with 2 groups of spigots, each group with 3–4 long spigots (Gs, Fig. 4E–G ). Male palp and epigyne as for the species.

Composition. Only the type species. Two other species, Styposis clausis Levi, 1960 and S. selis Levi, 1964 , may also belong to this genus. Although S. clausis has 6 bulged eyes, 3 promarginal cheliceral teeth in male, serrate median apophysis and tegular pit (see Heimer & Müller 1991: figs 1–8) its tarsi are shorter than metatarsi, sternum is not bulged and petiolus is located in anterior part of abdomen. Styposis selis Levi, 1964 (see Levi 1964: figs 4–9) has 6 bulged eyes, similar male palp, and tarsi I in both sexes longer that metatarsi, but it has no bulged sternum, petiolus is located in anterior part of abdomen and has epigyne of different shape.

Figures

FIGURE 1. General appearance of Glebych minutissumus sp. n. of the male (A–D) and female (E–F). A prosoma, dorsal; B, E body, lateral; C, F body, ventral; D prosoma, dorso-lateral. Scale = 0.2 mm. Abbreviation: Ts tracheal spiracle.

FIGURE 2. SEM images of Glebych minutissimus sp. n., male (A–E, G–I) and female (F, J–K). A–B prosoma, lateral and frontal; C eye group; D spinnerets and colulus; E posterior part of abdomen; F–H chelicera; I terminal part of cymbium with removed bulb showing cymbial spoor; J–K epigyne, ventro-lateral and antero-ventral. Scale = 0.1 mm, unless otherwise indicated. Abbreviations: Cl colulus, Cs cymbial spur, Ep epigynal plate, MAP major ampulate gland spigot, Me median plate of epigyne, Oc copulatory opening, Ss strong seta of cymbial spur, Ts tracheal spiracle.

FIGURE 3. SEM images of the male palp of Glebych minutissimus sp. n. A–C intact, meso-ventral, ecto-ventral and ecto-dorsal; D–I expanded palp, different views. Scale = 0.1 mm.Abbreviations: Co conductor, Cs cymbial spur, Eb embolic base, Em embolus, Ma median apophysis, Mp anterior process of median apophysis, Sm serrate retrolateral margin, Ss strong seta of Cs, Tp retrolateral pit of tegulum.

FIGURE 4. Glebych minutissimus sp. n., male (A, B, D–G) and female (C, H–L). A prosoma, frontal; B tarsus IV; C palp; D leg I; E abdomen; F–G epiandrus (two individuals); H epigyne, ventral; I–J epigyne, antero-ventral; K epigyne and uterus internus, antero-ventral; L abdomen, antero-ventral. Scale = 0.1 mm. Abbreviations: Cd copulatory duct, Ea epiandrus, Gs gland spigot, Me median plate of epigyne, Oc copulatory opening Re receptacle, To tarsal organ.