Collembola from Two Samplings in the MSS of the Sierra de Guadarrama National Park in Two Different Seasons, with Description of a New Species

Simple Summary The interest in the fauna of the colluvial mesovoid shallow substratum (MSS) led us to install a series of pitfall traps (subterranean sampling devices or SSDs) for a full year in the Sierra de Guadarrama. This paper presents the comparative results between the captures at two different periods of the year and allows the description of a new species, found only in one of those periods. It seems proven that there are species present throughout the year, but others also predominate, or are exclusive, to just one of them. This study indicates, again, that the colluvial MSS has a particular species composition for the taxon Collembola, different from the surface, a perfectly differentiated habitat. Abstract An intensive sampling in a colluvial mesovoid shallow substratum (MSS) of the Sierra de Guadarrama National Park, using 33 subterranean sampling devices (SSDs) is the origin of the Collembola studied in this paper. The data were obtained from the second extraction of the traps, in operation between October of 2015 and May of 2016. This paper presents the faunistic and diversity data along with the entire park (mostly at sampling points above 200 m a.s.l.) for this period, compares the data between the first extraction of the traps and the second one, and describes one species of the genus Pseudosinella that appears as new in the second campaign.


Introduction
The mesovoid shallow substratum (MSS) consists of a network of interstices and subsoil fissures, and harbors diverse epigean species of a stenoic nature, and strictly hypogean species, permanent inhabitants of this environment [1,2]. Previous studies were focused on ecology [3,4], or faunal aspects [5][6][7]. Some studies on the MSS have been carried out in karstic areas. In a karstic environment, there are caves, and the scree-slope can be an intermediate place between the caves and the outside environment. The springtails that live in caves are not really from caves but from the infractions of the karstic terrain, which by definition is very broken. There are no caves in terrains such as the MSS de Guadarrama. In this paper, a continuation of five previously published [8][9][10][11], the fauna found in the same traps but in different periods of the year is compared, for a complete season. In addition to an important substitution of species between seasons, in the second period, a new species for science (Pseudosinella) that had not been captured in the first was (a) five locations in Siete Picos and La Mujer Muerta, of which four had double SSDs (1 m and 0.5 m); (b) 15 localities in Montes Carpetanos, one of which had two TSPs installed and the remaining 14 an SSD of 1 m in length; (c) 12 localities with SSDs of 1 m in length, located in Cuerda Larga and its associated mountainous complex; and (d) two in Puerto de los Cotos-Puerto de Navacerrada. The methodology used for sampling was described in detail in Baquero et al. (2017) [8].

Faunistic
The data for the taxon Collembola obtained from the first period were: 42,735 specimens, 31 genera and 65 species (16 new species). In this period, the most representative genus was Orchesella, represented by two new species (Baquero et al. 2017) [8]. In the second period, catches were significantly lower: 20,098 specimens, two genera were added (Caprainea and Ceratophysella), and 13 species not caught in the initial period. Twenty-six of the species captured in the first period were not captured in this one.
If the taxonomic groups lower than Collembola (Orders and Families) are considered (only those that provide sufficient abundance to allow a comparison to be made) it can be said that: Entomobryomorpha specimens decrease in the second period; Poduromorpha behaves differently depending on the family, with the Hypogastruridae decreasing and the Onychiuridae increasing; Symphypleona, in general, increases considerably, although there is a family (Sminthuridae) that suffers an appreciable decline.
Given that the traps had been in the field for a period of six months, and the specimens deteriorate over time, especially if they are not submerged in propylene glycol promptly, some identifications refer to specimens that had fallen into the trap close to its collection date.
Retinaculum with 4 + 4 teeth. Furca well developed. Ratio dens/mucro: 1.79. Dens with medium size granulation and two prominent tubercles between the two more distal chaetae (variable shape between specimens); seven dorsal chaetae of which one of the basal is slightly longer. Mucro with a sharpening tip, and with clear outer lamella (variable shape between specimens) ( Figure 7B).
Anal spines 0.8 times shorter than inner edge of claw, slightly curved, situated on long papillae the same length as the colorless spine ( Figure 6).

Ecology
In this project, five samples appeared, three in the highest part of the Montes Carpetanos (SSD-08, SSD-17 and SSD-21) and two on the north-face of La Mujer Muerta (SSD-01 and SSD-03). It seems linked to higher and colder areas. Tibiotarsi I, II, III with 19, 19, 18 chaetae, respectively, including a clavate tenent hair longer than the claw in each. Claws with a big inner tooth and two pairs of lateral teeth. Empodial appendage with broad basal lamella and apical filament reaching slightly below inner tooth (ratio empodial filament: inner edge of claw : 0.70) ( Figure 7A). Ventral tube with 4 + 4 chaetae (two apical and two basal).
Retinaculum with 4 + 4 teeth. Furca well developed. Ratio dens/mucro: 1.79. Dens with medium size granulation and two prominent tubercles between the two more distal chaetae (variable shape between specimens); seven dorsal chaetae of which one of the basal is slightly longer. Mucro with a sharpening tip, and with clear outer lamella (variable shape between specimens) ( Figure 7B).

Remarks
In 1955, Steiner [33] described a new species of Hypogastura s. str. from specimens collected above Cercedilla (Sierra de Guadarrama, Madrid, Spain). The description of the species is well documented but only the furca, the claw, and the anal spine are represented. We have considered important a re-description of this species due to the original description missing some characteristics that have recently been revealed as necessary. For this, not only the specimens collected by us (7851 ex.) but also four syntypes from the MNCN (Madrid) have been studied in detail. The species belongs to the armata-group (group B), Abd IV with p 1 as macrochaeta (Thibaud et al. 2004) [40] and subgroup B1 (Abd IV with chaeta p 3 ) (Bourgeois and Cassagnau 1972) [37]. It also has an accessory tubercle near the eyes on both sides of the head, similarly to C. sinensis Stach, 1964 [35] described from China, and also H. tooliki Fjellberg, 1985 [41], from Alaska and Magadan (Russia). The first species, unlike C. meridionalis, has the following diagnostic characteristics: color brown; body chaetae smooth; seven dorsal sensilla on dorsal, and some hook-like sensillum on the ventral side of Ant IV; head accessory tubercles are smooth, resembling a corneola; Insects 2022, 13, 1025 9 of 17 tenent hair short; empodial appendage short; dens basal chaeta two times the length of the other; dens without distal tubercles; dens to mucro ratio almost three times; mucro boat-like (rounded tip), and outer lamella not very developed; anal spines rounded at the tip, slender and not curved (Babenko et al. 1994) [38]. The second one has fine and uniform integumentary granulation, a weak difference between the body chaetae, all of them short and acuminate, body chaetae, and sensilla of the same size as the body chaetae. Anal spines 0.8 times shorter than inner edge of claw, slightly curved, situated on long papillae the same length as the colorless spine ( Figure 6).

Ecology
In this project, five samples appeared, three in the highest part of the Montes Carpetanos (SSD-08, SSD-17 and SSD-21) and two on the north-face of La Mujer Muerta (SSD-01 and SSD-03). It seems linked to higher and colder areas.

Remarks
In 1955, Steiner [33] described a new species of Hypogastura s. str. from specimens collected above Cercedilla (Sierra de Guadarrama, Madrid, Spain). The description of the species is well documented but only the furca, the claw, and the anal spine are represented. We have considered important a re-description of this species due to the original description missing some characteristics that have recently been revealed as necessary. For this, not only the specimens collected by us (7851 ex.) but also four syntypes from the MNCN (Madrid) have been studied in detail. The species belongs to the armata-group (group B), Abd IV with p1 as macrochaeta (Thibaud et al. 2004) [40] and subgroup B1 (Abd IV with chaeta p3) (Bourgeois and Cassagnau 1972) [37]. It also has an accessory tubercle near the eyes on both sides of the head, similarly to C. sinensis Stach, 1964 [35] described from China, and also H. tooliki Fjellberg, 1985 [41], from Alaska and Magadan (Russia). The first species, unlike C. meridionalis, has the following diagnostic characteristics: color brown; body chaetae smooth; seven dorsal sensilla on dorsal, and some hooklike sensillum on the ventral side of Ant IV; head accessory tubercles are smooth, resembling a corneola; tenent hair short; empodial appendage short; dens basal chaeta two times the length of the other; dens without distal tubercles; dens to mucro ratio almost three times; mucro boat-like (rounded tip), and outer lamella not very developed; anal spines None of the descriptions coincide with the description made, in his day, by Steiner or with the one made here. There is a clear heterochaetosis, with macrochaetae and microchaetae, the latter between 2/3 and 1/2 of the length of the Mc, all (Mc and mic) ciliated or with serrations, except for the sensilla that are smooth and longer or as long as the Mc. The furca is characteristic and as described by Steiner (1955) but has many sensilla and sensory chaetae of different types on the antenna ( Figure 7B); very different from Steiner's description and from that drawn by Jordana and Arbea in 1997 (Fauna Ibérica). Between Ant III and IV, the antenna has an eversible sac (Figure 3), characteristic of Ceratophysella. The shape of the PAO in Ceratophysella species is usually elongated (not as a rosette), as is also the case in this species.
When studying the definitions of the genera of Ceratophysella and Hypogastrura, it is observed that all the characteristics considered have exceptions, except heterochaetosis. In addition, since this species has clear heterochaetosis, it is considered to belong to the genus Ceratophysella. It is likely that DNA techniques can shed light on the difficulties of assigning a species to each of the genera. Order

Etymology
The name refers to the asymmetry of the prelabral chaetae, the central ones ciliated and the lateral ones smooth.

Diagnosis
Blue body pigment, including antennae and first leg segments. Head with 6 + 6 eyes; A 0 , A 2 and A 3 as Mc; basomedian labial fields chaetae smooth; posterior labial row with M 1 , m 2 , R*, e, L 1 and L 2 Mc; three plus one anterior postlabial chaetae as ciliate Mc. Th II-III without Mc; Abd II with chaeta a 2p present, a 3 forward from 'as' sensilla; a 2 as mic, and m 3 as ciliated Mc; Abd IV with three median mac (C 1 , B 5-6 ), four ciliated mic behind anterior bothriotrichum (some fan-shaped) and bothriothrichal complex mic D 1p present; claw with three internal teeth: two basal and one unpaired; empodium acuminate.

Description
Body length up to 1.90 mm, head included, excluding antennae (holotype: 1.80 mm). Color: dark blue on the whole body. Scales absent on antennae and legs, present on ventral and dorsal head, thorax, and abdomen dorsally, and furcula (dorsal and ventrally).
Furcula. Manubrium and dens with scales both dorsal and ventrally, and with the same length; manubrial plate with three internal and 14-16 external chaetae, and 2 pse ( Figure 11C). Non-ringed area of dens 3.5-4 times the length of mucro, with subapical tooth a little smaller than apical tooth. (Figure 11D).

Ecology
The species is scarcely distributed in the MSS of Sierra de Guadarrama since it has only been found at one of the sampling points. The sampling area, at 1818 m asl, in the oro-Mediterranean bioclimatic zone, has the important forest influence of Pinus sylvestris L. The rock substrate is orthogneisses (Vialette et al. 1987) [46], and its characteristics facilitate the fracture of this material, which allowed its fragmentation during glacial (Pedraza and Carrasco 2005) [47] and periglacial (Sanz 1986) [48] events, usually in the form of large and medium-sized scree. The MSS where SSD-2 was installed shows a profile with an accumulation of large rocks at higher levels, and as depths reach 1 m, the size of the rock is reduced. Infiltration of black earth rich in organic matter was observed, but the MSS conserves the subterranean tridimensional network of fissures and interstices.

Remarks
The species that share the traditional formula of Gisin are in addition to P. gonzaloi Baquero and Jordana, 2021, and P. valverdei Baquero and Jordana, 2021 [10]. P. gonzaloi has the sensilla of the Ant III sensory organ, being rod-like, all labral chaetae ciliated (at least on its half distal part), the eyes in other positions, chaeta E on ventral labial row ciliated, four teeth on internal or ventral claw, and a different number of chaetae on the manubrial plate (7)(8). P. valverdei has only five eyes, prelabral chaetae smooth, L 1 and L 2 chaetae on ventral labial row smooth, and four teeth on the internal or ventral claw. Curiously, these two species have been described in the same mountain massif. This species could have gone unnoticed among the thousands of specimens of Pseudosinella and Lepidocyrtus found in the first period. Most of the specimens were very deteriorated after remaining between several days and six months in the propylene glycol of the traps.  Legs. The legs are without scales. Trochanteral organ with 12-17 close spine-like chaetae ( Figure 11A). Claw with three teeth on inner edge: paired at 50% and unpaired at 75% with respect to the internal claw edge length; two lateral teeth at 10-20%, and basal dorsal. Empodium acuminate, all legs with serrated pe lamella (very minute serration on leg 3), other lamellae smooth (ae, ai, pi); claw:empodium ratio = 1:0.65. Tibiotarsus III distally with one inner smooth chaeta 0.60 longer than claw; tenent hairs capitate, smooth, and 0.70 shorter than claw ( Figure 11B).
Furcula. Manubrium and dens with scales both dorsal and ventrally, and with the same length; manubrial plate with three internal and 14-16 external chaetae, and 2 pse ( Figure 11C). Non-ringed area of dens 3.5-4 times the length of mucro, with subapical tooth a little smaller than apical tooth. (Figure 11D).
Macrochaetotaxy. Reduced formula (from Gisin 1965Gisin , 1967a [25][26][27]: R0R1R2000/00/0101 + 2/s, pABq1q2, M1m2R*eL1L2 (* ½ to 2/3 of M; sometimes M2 ciliated, asymmetric). Details in Figures 8 and 9. The species is scarcely distributed in the MSS of Sierra de Guadarrama since it has only been found at one of the sampling points. The sampling area, at 1818 m asl, in the oro-Mediterranean bioclimatic zone, has the important forest influence of Pinus sylvestris L. The rock substrate is orthogneisses (Vialette et al. 1987) [46], and its characteristics facilitate the fracture of this material, which allowed its fragmentation during glacial (Pedraza and Carrasco 2005) [47] and periglacial (Sanz 1986) [48] events, usually in the form of large and medium-sized scree. The MSS where SSD-2 was installed shows a profile with an accumulation of large rocks at higher levels, and as depths reach 1 m, the size of the rock is reduced. Infiltration of black earth rich in organic matter was observed, but the MSS conserves the subterranean tridimensional network of fissures and interstices.

Remarks
The species that share the traditional formula of Gisin are in addition to P. gonzaloi Baquero and Jordana, 2021, and P. valverdei Baquero and Jordana, 2021 [10]. P. gonzaloi has the sensilla of the Ant III sensory organ, being rod-like, all labral chaetae ciliated (at least on its half distal part), the eyes in other positions, chaeta E on ventral labial row ciliated,

General Discussion
The difference between the catches of the first period and the second, when comparing the species found, is striking. Many of the species well represented and in abundance during the period between May and October went from high numbers (tens of thousands of individuals) to only hundreds in the following period (October to May), and in some cases, even a few units or disappear (Entomobrya ledesmai Jordana and Baquero, 2021 and Pseudosinella gonzaloi Baquero and Jordana, 2021) (see Table 2). The opposite also happens: species little represented in the first period increase in their abundance in the second, going from hundreds to thousands, even in one case, from complete absence to being one of the most abundant species with thousands of specimens (Lepidocyrtus labyrinthi Baquero and Jordana, 2021 and Hypogastrura papillata Gisin, 1949 [49]). There is a case to comment on: C. meridionalis Steiner, 1955 [33] was the most abundant species in the first period and seemed to be replaced by H. papillata. During the placement of the traps, a few weeks before the month of May, it was possible to see accumulations of this species on the surface, under the slabs of cattle excrement in the highland meadows. This indicates that it is present, at least during part of the year, on the surface of the ground. Finding it during the following months in the MSS confirms that it moves vertically on the ground during the year, and the fact that between May and October 621 specimens were captured in the traps indicates that during this period it prefers the surface.
This reasoning cannot be applied to other abundant species between May and October (Orchesella colluvialis, Lepidocyrtus paralignorum, Entomobrya guadarramensis, E. ledesmai) since they are not species detected on the surface at any time before. The decrease in their abundance between May and October must be due to other reasons; for example, biological cycles adapted to temperature or food availability.
No reference has been made to other papers that refer to karstic MSS because this biotope is granitic. The fauna found in this granitic MSS is mainly its own fauna, as has been shown in our previous works. This study indicates that the colluvial MSS has a particular species composition for the taxon Collembola, demonstrating that the MSS should not be considered a mere ecotone between the surface and the deep subterranean ecosystem, but rather as a perfectly differentiated habitat. Table 2. Total list of species found in the sampling, in the two sessions, ordered by abundance for the first extraction from the traps. The numbers are the total number of specimens for each species.

Species
May-October October-May Total  Institutional Review Board Statement: Ethical review and approval were waived for this study, due to Spanish laws, which do not require permission from an institutional ethics committee on the use of animals for taxonomical studies with micro-arthropods. Data Availability Statement: All data is contained within the article. Collected specimens have been deposited in the collection of the Museum of Zoology, Department of Environmental Biology, University of Navarra (MZNA).