A further contribution to the knowledge of Pectiniunguis minutus (Demange, 1968), a little known dwarf schendylid centipede from western equatorial Africa (Chilopoda: Geophilomorpha)

The geophilomorph centipede Pectiniunguis minutus (Demange, 1968), a little known dwarf schendylid from Gabon (Western equatorial Africa), is redescribed and illustrated based on the type material and an additional non-type specimen preserved in the collections of the Muséum national d’Histoire naturelle, Paris. P. minutus can be easily differentiated from all the other species currently assigned to the genus Pectiniunguis, by the very low number of leg-bearing segments (35 in the males, 37 or 39 in the females) and very small body size (12-16 mm in length). P. minutus is also distinguished by having ventral pore-fields on the anterior region of the body only, this character being shared by a single species of the genus, i.e., P. ascendens Pereira, Minelli & Barbieri, 1994, from the Neotropics (Brazil: State of Amazonas) with which a morphological comparison is given. Comments about other dwarf centipede species belonging to several families of the order Geophilomorpha, are also added. Key-Words: Pectiniunguis; Taxonomy; Western Equatorial Africa; Chilopoda; Geophilomorpha; Schendylidae.


IntroductIon
Two hundred and nineteen species, in thirtythree genera are currently recognized in the geophilomorph family Schendylidae.The taxon occurs in the Americas including the Antilles; Europe and central-northern Asia, including the Japanese region; scattered records from Africa; Madagascar; from Indochina, through Indonesia, to Australia, New Caledonia, Hawaii and the Fiji Islands (Pereira et al., 1997;Bonato et al., 2009).
In sub-Saharan Africa the family currently includes twenty-three species in four genera: six species in the genus Mesoschendyla Attems, 1909;five in Schendylops Cook, 1899;11 in Ctenophilus Cook, 1896 and one in Pectiniunguis Bollman, 1889.The species of the first two genera are distributed in the equatorial and southernmost regions, while those of the two latter occur in the western equatorial region only.These four taxa are also widespread elsewhere: Mesoschendyla also occurs in Madagascar (one species) and Java (one species); Schendylops in Northern mainland Africa (two species), Madagascar (5 species), and the Neotropical Region (54 species); Ctenophilus in the Neotropics (one species); and Pectiniunguis in Oceania Region (one species in Fiji Islands), and the New World (21 species) distributed in southern North America (U.S.A), Central America (Mexico), Caribbean Islands (Cuba and Cayo Sombrero (Venezuela)), South American mainland (Colombia, Guyana, continental Ecuador, Brazil and Argentina), and the Galápagos Islands.The last survey of Mesoschendyla can be found in Crabill 1968.Recent contributions to the study of the species of Schendylops from mainland Africa include Pereira & Minelli, 1995, 2001; studies on those inhabiting Madagascar comprise Hoffman & Pereira, 1997;Pereira et al., 2004.The African species of Ctenophilus were revised by Pereira & Demange, 1991, 1997.Latest contributions to the knowledge of the Neotropical species of Pectiniunguis can be found in Pereira & Coscarón, 1975(1976); Pereira et al., 1994Pereira et al., , 1995Pereira et al., , 1999Pereira et al., , 2000Pereira et al., , 2001;;Shear & Peck, 1992;Pereira, 2010a; the single species from Fiji Islands was revised by Pereira, 1982.The purpose of the present contribution is to redescribe the only known representative of the genus Pectiniunguis from Africa (Gabon), which was described by Demange (1968) under the name of Pleuroschendyla minuta.The original description lacks information on many important characters of specific value and only includes two inadequately detailed figures.Pereira & Demange (1991) revised the holotype and transferred the species to the genus Pectiniunguis on the basis of the morphological features of the pleurites of the second maxillae, but besides the proposal of the new combination [Pectiniunguis minutus (Demange, 1968)], no additional morphological data, nor new illustrations were given.Subsequently, no other authors have treated this taxon which has remained poorly known.The opportunity to revise all the type material and an additional non-type specimen during a visit to the Laboratoire de Zoologie (Arthropodes), Muséum national d'Histoire naturelle, Paris, allows a detailed redescription with new illustrations, giving a better understanding of this interesting dwarf schendylid centipede.

MAterIAl And Methods
The type and non-type material herein revised, is currently housed at the Muséum national d'Histoire naturelle, Paris (MNHN).
The specimens were examined and illustrated using a compound microscope equipped with a drawing tube attachment.Temporary mounts were prepared by direct transfer of the specimens from the preservation liquid (70 per cent ethanol) onto microscope slides, using as a clearing agent/mounting medium, undiluted 2-Phenoxyethanol (CAS No. 122-99-6).Details on preparation of microscope slides and employed dissection procedures are described in Pereira (2000Pereira ( , 2010aPereira ( , 2010b)); Foddai et al. (2002).All measurements are given in mm.Terminology for the external anatomy follows Bonato et al. (2010Bonato et al. ( , 2011)).The following abbreviation was used in the text and legends of the figures: a.a., antennal article/articles.

Family schendylidae Genus Pectiniunguis bollman, 1889
Diagnosis: This genus can be distinguished from other genera currently recognized in the family Schendylidae by the following particular combination of features.Second maxillae: pleurites not fused to the posterior internal border of the coxosternite, apical claw of telopodites pectinate on both dorsal and ventral edge.Sternites: with pore-fields.Ultimate leg-bearing segment: ultimate legs with seven articles, pretarsus in form of a small hairy tubercle or replaced by a small spine or altogether absent, each coxopleuron with two internal coxal organs of composite structure ("heterogeneous coxal glands" sensu Brölemann & Ribaut (1912)).
Type species of the genus: Pectiniunguis americanus Bollman, 1889, by original designation.

Remarks:
The original description mentions the four specimens cited above, and an additional non type from "Bélinga: Station 129 T, carrière, route du débarcadère, Forêt tropicale" (sex and number of legbearing segments not specified), but this latter was not revised in the present study.
Antennae: ca.2.4 times as long as the cephalic plate, distally slightly attenuate; a.a.II to XIII all wider than long, a.a.XIV longer than wide (Fig. 1).Setae on a.a.I to VI of different lengths and few in number, those of remaining articles progressively shorter and more numerous towards the tip of the appendage (Fig. 1).Apical a.a. with ca. 15 claviform sensilla on the external border and absent on the internal border (similar to the holotype, Fig. 36); distal end of this a.a. with ca. 4 specialized sensilla apparently not split apically, (similar to the holotype, Fig. 36).2.
Labrum: with 18 small teeth, those of the central arc dark and round tipped, the lateral ones less sclerotized, each with a very sharp medial extension (Fig. 10).
Forcipular segment: when closed, the telopodites do not extend beyond the anterior margin of the head.Forcipular tergite with an irregular transverse median row of ca. 12 large setae and a few additional smaller setae scattered on the remaining surface.All articles of the telopodites without teeth.Poison glands unusually large (shape and relative size as in Fig. 16: c).Calyx of poison gland subcylindrical and very short (Figs. 16,17: b).Pilosity of coxosternite and telopodites as in Figure 16.
Walking legs: chaetotaxy similar throughout the entire body length.Distribution, number and relative size of setae as in Fig. 18.Claws with two thin and pale accessory spines ventrobasally, one anterior and one posterior (shape and relative size as in Fig. 19).
Female allotype: Thirty-seven leg-bearing segments, body length 13 mm, maximum body width 0.60 mm.All features similar to those in the male except for the shape and chaetotaxy of the ultimate leg-bearing segment and postpedal segments.
Variation: males with 35, and females with 37 or 39 leg-bearing segments.
The posterior limit of the ventral pore-field series is at the sternite 20 in the male holotype and male paratype (both with 35 leg-bearing segments); sternite 22 in the female allotype (with 37 leg-bearing segments); and sternite 28 in the non-type female (with 39 leg-bearing segments).
The body is (according to the original description) "12-16 mm" long.(View comments on this trait, below).
Other features with non-significant variation.

Remarks:
The adult condition of the four specimens herein revised is indicated by the tubula seminifera full of mature spermatozoa in the males, and the two spermathecae full of spermatozoa in the females.
The original description by Demange is very short, only includes two figures (labrum, and ultimate leg-bearing segment and postpedal segments in ventral view), and completely lacks information on chaetotaxy of the antennae; kind and number of specialized sensilla on a.a.II, V, IX and XIII; pilosity of clypeus; shape and chaetotaxy of the forcipular segment; relative size of the ventral pore-fields; pilosity of walking legs; details of internal structure of the coxal organs; form of pretarsus of the ultimate legs; shape of the female postpedal segments; etc.
The author states "champs poreux présents du 2e segment au 21-22e segment" (but the posterior limit of the ventral pore-field series varies as detailed above).Of the body length he says "12-16 mm", but none of the four specimens here revised exceeds 13 mm in length, "16 mm" could refer to the specimen from "Bélinga.Station 29 T, carrière, route du débarcadère.Forêt tropicale" (not examined in the present contribution, as stated above).
Known range: Only known from the type locality.

dIscussIon
The original description of Pectiniunguis minutus mentions as type locality the Bélinga region in Gabon (which according to White (1983) is part of the Guineo-Congolian rainforest).No data are given on the collecting sites of the three type specimens, however it is stated for the two non type specimens that they come from sites in a tropical forest environment (but the altitude a.s.l. is not given).In western equatorial Africa, the tropical lowland rainforest of Gabon is well known for its high biodiversity (Sosef 1994); according to Ngomanda et al. (2009) this forest is today well conserved because of the absence of intensive agricultural activities, coupled with low population densities.(Nevertheless, the biodiversity in the Bélinga mountains    (15, 19); 0.1 mm (13, 17-18); 0.2 mm (14, 16). is threatened by global warming and iron mining (Leal, 2008)).
P. minutus is characterized by having thin and pale accessory spines on the claws of the walking legs (Fig. 19), this trait is shared by most of the species of Pectiniunguis inhabiting South America and the one from the Fiji Islands.(The opposite condition, i.e., strong and dark accessory spines, occur in some members distributed in southern North America, Central America, West Indies and Northwestern South America, e.g., P. bollmani Pereira, Minelli & Foddai, 1999 from Venezuela (Fig. 48)).Among the species currently recognized in the genus, only P. ascendens Pereira, Minelli & Barbieri, 1994, from the Neotropical Region (Brazil: State of Amazonas) shares with P. minutus the peculiarity of bearing ventral pore-fields on the anterior region of the body only.These two species also share a similar shape of pretarsus of the ultimate legs (represented by a rudimentary tubercle with 2 diminutive spines); a similar internal chitinous structure of the coxal organs (showing one to three individualized areas of mucous layer for each outer lobe); presence of specialized brownish-ochre sensilla, on dorsal side of some a.a.A morphological comparison of these apparently similar taxa, can be made by means of the following selected traits (those for P. ascendens are given in parentheses): males with 35, females with 37 or 39 leg-bearing segments     As mentioned above, Pectiniunguis minutus was originally placed in the genus Pleuroschendyla Brölemann & Ribaut, 1911, for which the current valid name is Ctenophilus Cook, 1896 (senior synonym of the first).Twelve species are currently included in Ctenophilus; Pectiniunguis minutus can be easily differentiated from all of them by the shape of the pleurites of the second maxillae which are not fused to the posterior internal border of the coxosternite (Figs. 14,(37)(38)(39).(In all species at present assigned to Ctenophilus, those pleurites are fused to the postero-internal area of the second maxillary coxosternite, as shown in Fig. 44).At least five African species of Ctenophilus share with P. minutus the particularity of having pore-fields on the anterior region of the body only: C. angolae (Chamberlin, 1951) (from Zaire: Gombe Louzi, Thysville; Angola: Dundo); C. corticeus (Demange, 1968) (from Gabon: Bélinga); C. edentulus (Porat, 1894) (from Camerun: Bonge, Olounou; Gabon: Makokou, Bélinga); C. nitidus (Brölemann, 1926) (from Bénin: Athiémé) and C. oligopodus (Demange, 1963) (from Ivory Coast: Mont Nimba).(But in its original description, P. minutus is compared with the latter only).
It remains to be seen whether the numerous species of Schendylidae currently referred to the genus Pectiniunguis really form a monophyletic unit.Their geographical distribution with a majority of species in the New World, accompanied by a single one on mainland Africa, and one in the Oceania region, invites closer investigation; but a phylogenetical study is not an easy task as the whole generic classification of schendylid geophilomorphs is still based on characters of uncertain phylogenetic value.
Only three species of Schendylidae (in two genera) are known to occur in Gabon: Ctenophilus corticeus (Demange, 1968), Ctenophilus edentulus (Porat, 1894) and Pectiniunguis minutus (Demange, 1968).They may only represent a small portion of the biodiversity of the family in the rich tropical rainforest biome of that country.It is possible that intensive field work on the whole extension of the region, may result in the discovery of new taxa of geophilomorph centipedes.

AcknowledGeMents
I am indebted to Jean-Paul Mauriès, Monique Nguyen Duy-Jacquemin, Jean-Marie Demange and Jean-Jacques Geoffroy of the Muséum national d'Histoire naturelle, Paris for the access to relevant specimens, library facilities, valuable guidance and hospitality in the Laboratoire de Zoologie (Arthropodes) during part of this study.I am also grateful to the Museum authorities for the financial support that enabled my stay at the institution.Miguel E. Leal and James C. Solomon (Missouri Botanical Garden, St. Louis), provided information on environmental features and biodiversity of the Bélinga mountains, Gabon.Two anonymous referees contributed with careful reviews which helped to improve the final version of the manuscript.Carlos José Einicker Lamas (Museu de Zoologia da Universidade de São Paulo), as well as Adriana Nascimento Flamino and Airton de Almeida Cruz (of the same institution), very kindly assisted me during all steps of the review and publication process.Hernán Lucas Pereira (La Plata) prepared the electronic versions of the figures.
Dorsal and ventral surface of a.a.II, V, IX and XIII (Figs.2-7) with very small specialized sensilla.On the ventral side these sensilla are restricted to an internal latero-apical area and are represented by two different types: a and b.Type a sensilla are very thin and not divided apically (Fig.5: a); type b sensilla are similar to those on the apex of the terminal a.a.but with two very small apical branches (Fig.5: b).Specialized sensilla on dorsal side restricted to an external latero-apical area on a.a.II, V and IX(Figs.2, 4, 6)  and to an internal and external sublateral apical areas on a.a.XIII (Fig.7), and are represented by three different types: a, similar to a of ventral side (Fig.7: a); b, similar to b of ventral side, with two very small apical branches on a.a.II (Fig. 2: b) but apparently not divided apically on a.a.V, IX and XIII (Figs. 4, 6-7: b); and type c sensilla, much bigger than type b, not divided apically and darker (brownish-ochre in colour) (Figs.6-7: c).Distribution of type a, b and c sensilla on a.a.II, V, IX and XIII as in Table

Figs. 11
Figs. 11-12 (divided in three blocks); claw of walking legs with two accessory spines, one anterior and one posterior, Fig.19(with three accessory spines, one anterior and two posterior, Fig.46).(The precedent comparison, merely express similarities and differences between presumptively morphologically similar species.Phylogenetic relationships can only be elucidate through appropriate analyses).