Micropholcus Deeleman-Reinhold & Prinsen, SEM 1987
Creators: name: Huber, Bernhard A.
name: Meng, Guanliang
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Araneae
Pholcidae
Micropholcus

description: GenusMicropholcusDeeleman-Reinhold & Prinsen, 1987
Micropholcus Deeleman-Reinhold & Prinsen, 1987: 73; type species: Pholcus fauroti Simon, 1887.
Micropholcus – Deeleman-Reinhold and van Harten 2001: 199. Huber 2011: 24. Huber et al. 2014: 435.
Mariguitaia González-Sponga, 2004: 66; type species: Mariguitaia divergentis Gonzalez-Sponga 2004. Synonymised in Huber 2009.
Diagnosis.
Old World species are long-legged, eight-eyed pholcids with an oval abdomen (Figs 3, 4); New World species are more variable, sometimes without AME, sometimes with elongate to worm-shaped abdomens. Most known species (except M. bukidnon sp. nov.) with unique modified hair at tip of male palpal trochanter apophysis (Fig. 9 A – D; see also Huber 2000: figs 105, 106; Huber and Wunderlich 2006: figs 4 h, 8 d; Huber 2011: fig. 95; Huber et al. 2014: figs 32, 57). Male chelicerae with frontal apophyses with modified hairs (Fig. 6), i. e., similar to putative sister genus Cantikus Huber but different from other close relatives (Leptopholcus Simon, Pehrforsskalia Deeleman-Reinhold & van Harten, and Micromerys Bradley). Procursus and bulb morphology highly variable and not diagnostic at genus level (contra Huber 2011). Females not diagnosable morphologically at genus level (highly variable and similar to closely related genera).
Note.
Most parts in this general section about Micropholcus refer to the entire genus. The following description is limited to Old World taxa because they are relatively homogeneous, while some New World species (in particular those on the Caribbean islands) are superficially extremely different from South American (in particular Brazilian) and Old World species.
Description
(Old World taxa). Male. Measurements. Total body length ~ 2.3–3.9. Carapace width 0.8–1.5. Diameter PME 60–100 µm; diameter AME usually 35–55 µm, in M. bukidnon sp. nov. only 15 µm. Tibia 1 length 5.0–10.2. Tibia 1 L / d: 57–85. Leg formula 1243. Diameters of leg femora (at half length) 80–150 µm, of leg tibiae 75–120 µm.
Colour (in ethanol). Prosoma and legs pale ochre-yellow to grey, carapace with dark pattern, legs with darker patellae and tibia-metatarsus joints; abdomen ochre-grey to whitish, monochromous or with whitish marks. Live specimens (Figs 3, 4) similar in colour but slightly darker.
Body. Ocular area slightly raised (distinct in frontal view; Fig. 5). Carapace without thoracic groove. Clypeus unmodified. Sternum slightly wider than long, unmodified. Abdomen approximately twice as long as wide. Gonopore with four (rarely five) epiandrous spigots (Fig. 10; see also Huber 2000: fig. 123; Huber 2011: fig. 99). ALS with one strongly widened spigot, one long pointed spigot, and six cylindrical spigots (Fig. 9; see also Huber 2000: figs 158, 159; Huber 2011: fig. 100); PMS with two conical spigots; PLS without spigots.
Chelicerae. Chelicerae with pair of strong frontal apophyses provided with conical or globular, strongly sculptured modified hairs (Fig. 6; see also Huber 2011: fig. 98), usually with one or two pairs of proximal processes; without stridulatory files.
Palps. Palpal coxa unmodified. Trochanter with retrolateral-ventral apophysis usually with distinctive modified (short cylindrical) hair at tip (Fig. 9 A – D), modified hair absent in M. bukidnon sp. nov. Femur variable in shape, often with rounded processes (usually ventrally and retrolaterally, sometimes also dorsally). Femur-patella joints shifted towards prolateral side. Tibia larger than femur, with two trichobothria. Tibia-tarsus joints shifted towards retrolateral side. Palpal tarsus with large capsulate tarsal organ (Fig. 11 H, I; see also Huber 2011: fig. 97), outer diameter 30–35 µm, diameter of opening 15–20 µm; more open (almost exposed) in M. bukidnon sp. nov. (Fig. 11 J). Procursus complex, often with distinct dorsal hinged process (e. g., Figs 16 C, 43 C, 52 C), in most species with transparent prolateral membranous flap densely set with teeth (Figs 7 A, D, 8 B). Genital bulb with distinct proximal sclerite connecting to tarsus, membranous or partly sclerotised embolus, and variably complex set of sclerotised apophyses, sometimes likely homologues of the Pholcus ‘ appendix’ and ‘ uncus’, sometimes of uncertain homology (Figs 7 B, F, 8 C, E, F, H).
Legs. Without spines and curved hairs. Without slender metatarsal hairs (cf. Huber et al. 2023 a). Without sexually dimorphic short vertical hairs. Chemoreceptive hairs ~ 20–25 µm long, with few side branches (Fig. 12 A, H), mostly near leg tips. Retrolateral trichobothrium of tibia 1 at 5–10 % of tibia length. Prolateral trichobothrium absent on tibia 1, present on tibiae 2–4. Base of trichobothria evenly rounded, without proximal ridge (cf. Fig. 11 D). Legs with roundish cuticular plates (Fig. 12 E; diameter ~ 6–8 µm) and rimmed pores (Fig. 12 B; outer diameter 2 µm, diameter of opening 0.2 µm) apparently on all leg segments. Tarsus 1 with ~ 20–30 pseudosegments, distally usually fairly distinct. Leg tarsal organs capsulate (Figs 11 E – G, 12 F; diameter 12–17 µm, diameter of opening 5–7 µm). Tarsus 4 with single row of comb-hairs on prolateral side (Fig. 12 G, H; see also Huber 2011: fig. 96). Main tarsal claws with ~ 10 teeth (Fig. 12 C, D).
Female. In general, very similar to males (Figs 3, 4). Legs slightly shorter than in males (male / female tibia 1 length: ~ 1.1–1.4, but sample sizes mostly small); tibia 1 length 4.3–9.1. Palpal tarsal organ smaller than in males (outer diameter: 18–25 µm, diameter of opening: 6–10 µm). Palpal tarsus ending distally in pointed tip and pair of strong dorsal hairs (Fig. 5 G, H). Spinnerets, leg hairs, cuticular plates, rimmed pores, comb-hairs, leg tarsal organs, and tarsal claws as in male. Epigynum anterior plate usually weakly sclerotised, with rounded process (‘ knob’; Fig. 11 A – C) in varying position; posterior epigynal plate short and indistinct. Internal genitalia often complex, highly variable, with distinct pair of pore plates.
Distribution.
The type species Micropholcus fauroti has attained a circumtropical distribution, with most records from between 25 ° S and 30 ° N (Fig. 5 A).
Micropholcus is one of only two Pholcidae genera (together with Pholcus) with autochthonous species in both the Old and New Worlds. New World species are mostly known from the Greater Antilles and from semi-arid regions in Brazil; the genus seems to be largely absent from the humid regions of the Amazon basin. Old World species are currently known from the Arabian Peninsula, Morocco, and the Philippines (Fig. 5 B – D). Specimens have been collected from sea level to 2370 m. In Saudi Arabia, all new species described herein were collected above 1200 m. Several of the localities visited below 1000 m had suitable habitats but no Micropholcus.
Natural history.
Old World Micropholcus seem to be very homogeneous with respect to their preferred microhabitats. Most species have been collected from rocks: in caves and at cave entrances, in small caverns of rock walls, and on the undersides of large boulders (Fig. 14). They share this type of microhabitat with most South American species, and with the majority of species of the putative sister genus (Cantikus), suggesting that this might be the plesiomorphic microhabitat. The unusual microhabitat reported for M. jacominae (dry plant debris in an irrigated banana plantation) needs confirmation. The synanthropic M. fauroti is usually found in the upper corners and edges of rooms. Caribbean species have shifted to the undersides of leaves, probably explaining their significantly different general body shape and colour (see Huber and Wunderlich 2006; Huber et al. 2014).
Old World and Brazilian Micropholcus spiders build fine dome-shaped webs but during the day, most species (except those deeper in caves, e. g., M. ghar sp. nov.) sit flat on the rock surface (Fig. 15). The webs of leaf-dwelling Caribbean species have not yet been described. Upon disturbance, the spiders show a range of reactions, from refusing to move, bouncing, walking or running away, to dropping out of the web. Egg sacs are round (in Caribbean species elongated), covered by a barely visible sparse layer of silk (Figs 3, 4), and contain up to ~ 35 eggs; egg diameters range from 0.54 to 0.71 mm. For more detailed observations on Brazilian species, see Huber et al. (2014). For detailed life history data of M. fauroti under lab conditions see Ahmad and Abou-Setta (2017). For anecdotal observations on further Old World species, see individual species descriptions below.
Relationships.
The molecular analysis of Eberle et al. (2018) placed Micropholcus as sister to the South-East Asian genus Cantikus Huber, 2018, within a clade that included three further Old World genera: Leptopholcus Simon, 1893; Pehrforsskalia Deeleman-Reinhold & van Harten, 2001; and Micromerys Bradley, 1877. That analysis included ten species of Micropholcus: the type species M. fauroti, two further Old World species (M. agadir and M. bukidnon sp. nov.) and seven New World species. The monophyly of the genus received maximum support. New World species were nested within a paraphyletic Old World group.
Our NJ tree (Fig. 1) is not expected to reliably reflect phylogenetic relationships. However, some clades that receive reasonable to high support are either congruent with the results of Eberle et al. (2018) (Caribbean clade) or include geographically neighbouring species: the Moroccan clade, the southern Saudi Arabian clade, and the northern Saudi Arabian clade. The latter two are also supported by several morphological similarities each, but it is not clear which of these are synapomorphies and which not. Thus, relationships within Micropholcus are largely unresolved and Fig. 1 should not be misinterpreted in a phylogenetic context.
Composition.
The genus now includes 30 described species: the Dominican amber fossil M. kiskeya (Huber & Wunderlich, 2006) and 29 extant species. Of the latter, seven occur in South America, six on the Caribbean islands, and 16 in the Old World. All Old World species are treated below except for M. tegulifer Barrientos, 2019 (a loan request was denied by the curator of arthropods, Museu de Ciències Naturals de Barcelona). Numerous undescribed New World species are available in collections, in particular from Brazil (L. S. Carvalho, pers. comm. 2 July 2020). At least one further undescribed species is known to occur in Morocco, represented by a single male specimen deposited in the Muséum d’histoire naturelle, Genève, Switzerland (“ sp. Gen 377 ” in Fig. 13 D). It resembles M. tegulifer but has a very different uncus. It originates from the Gorges du Dades area in the Drâa-Tafilalet Region, ~ 31.535 ° N, 5.918 ° W. Our molecular data indicate that the “ Pholcus sp. ” CO 1 barcode published in Dimitrov et al. (2008) is also from a Micropholcus, different from M. agadir, M. ghar sp. nov., and M. khenifra sp. nov. (Figs 1, 2). It could be M. tegulifer, M. sp. Gen 377, or a different new species. Its geographic origin cannot be reconstructed, and the only available (juvenile) specimen is lost (D. Dimitrov and C. Ribera, pers. comm. 20 Mar. and 19 Apr. 2024).
description: Published as part of Huber, Bernhard A. & Meng, Guanliang, 2024, Old World Micropholcus spiders, with first records of acrocerid parasitoids in Pholcidae (Araneae), pp. 95-182 in ZooKeys 1213 on pages 95-182, DOI: 10.3897/zookeys.1213.133178